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26th July 2022
Recently someone asked me about the status of Nuon emulation in MAME. I replied there was none. They asked why and I replied most likely because there was no good dumps of the ROMs and the hardware was quite complicated and not well documented. I pointed him to a thread on a forum that was started in 2015 that had some dev chatter about potential Nuon emulation. Initially it was thought that the system contained microcontrollers with internal ROM that would be undumpable and therefore can't be emulated. Later it was discovered that with a full dump it could possibly be emulated since the microcontroller didn't contain internal ROM. But nothing was done and it ended in 2018 with no solution. This person was passionate about the Nuon and asked what needed to be done. I suggested that if they wanted to see the Nuon emulated in MAME they would need to send a working unit to someone who makes things happen and could properly and fully dump it and document the hardware (i.e. me) to give the emulation a fighting chance of success.

So they did, and a unit arrived here about 2 weeks later last Friday.
The specific model that arrived is 'NUON Enhanced DVD Player / Samsung DVD-N501'.
I dumped the three chips holding data last night in about 10 minutes, then spent a good few hours writing up some documentation about the hardware inside and briefly summarizing the unit and software available based on info on the net.

A basic (totally non-working) skeleton driver was added to MAME today. After some work by someone who knows what they are doing I would expect to see it booting since the main CPU uses a common core (TLCS-900 family) and the boot ROM is easily dumped. But there will probably be nothing showing on screen since the graphics are generated by the Nuon processor and there is very little info about the Nuon processor so there may not be fully working emulation. But that's just a guess, I have not checked if any technical Nuon info is out there. There were dev kits made available to software developers back when the Nuon was current so if that has been made available publicly it will definitely help to better understand how the system works.

Additionally it was reported on May 29th 2022 that the authentication keys were discovered so that will help with homebrew software development for the Nuon. Previously homebrew only ran on the Samsung models but with this discovery it will be possible to run homebrew on all Nuon models. I'm sure we will see Doom on the Nuon eventually :-D

Either way, the wait is over and it's finally fully dumped.... 22 years later :-)

If anyone wants to donate one of the Nuon joysticks this will help with getting this unit I have into a working state so I can make some high quality reference videos of the games. Also I can reverse-engineer the joystick and make a duplicate so that a reproduction joystick can be produced or a common joystick can be converted. Up to now no one knows what's inside the Nuon joysticks so I would need to have one here to reverse it.

Here's some pics of the unit and a teardown of everything with lots of detail. The last few images are of interesting strings in the Nuon flash ROM, never before seen until now....
Samsung DVD-N501 Nuon DVD Player (main unit) Samsung DVD-N501 Nuon DVD Player (inside view) Samsung DVD-N501 Nuon DVD Player (power supply and jack board, top view) Samsung DVD-N501 Nuon DVD Player (power supply and jack board, bottom view) Samsung DVD-N501 Nuon DVD Player (vaccuum fluorescent display controller - NEC uPD78F0233 micro-controller) Samsung DVD-N501 Nuon DVD Player (video output IC for YPbPr, CVBS etc (Mitsumi MM1540A) Samsung DVD-N501 Nuon DVD Player (opamp and DAC area) Samsung DVD-N501 Nuon DVD Player (rear showing jacks) Samsung DVD-N501 Nuon DVD Player (rear close-up) Samsung DVD-N501 Nuon DVD Player (rear close-up) Samsung DVD-N501 Nuon DVD Player (rear close-up) Samsung DVD-N501 Nuon DVD Player (front bezel) Samsung DVD-N501 Nuon DVD Player (front bezel close-up) Samsung DVD-N501 Nuon DVD Player (front bezel close-up) Samsung DVD-N501 Nuon DVD Player (front bezel close-up of joystick ports) Samsung DVD-N501 Nuon DVD Player (front bezel inside) Samsung DVD-N501 Nuon DVD Player (close-up of vaccuum fluorescent display) Samsung DVD-N501 Nuon DVD Player (DVD drive) Samsung DVD-N501 Nuon DVD Player (DVD drive) Samsung DVD-N501 Nuon DVD Player (DVD drive) Samsung DVD-N501 Nuon DVD Player (main board) Samsung DVD-N501 Nuon DVD Player (main board) Samsung DVD-N501 Nuon DVD Player (main board) Samsung DVD-N501 Nuon DVD Player (main board showing Nuon processor and ROMs) Samsung DVD-N501 Nuon DVD Player (DVD drive sticker) Samsung DVD-N501 Nuon DVD Player (power board overview) Samsung DVD-N501 Nuon DVD Player (main board showing connectors/cables) Samsung DVD-N501 Nuon DVD Player (main board showing connectors/cables) Remote for Samsung NUON Enhanced DVD Player / Samsung DVD-N501
Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings) Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings) Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings) Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings) Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings) Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings) Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings) Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings) Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings) Samsung DVD-N501 Nuon DVD Player (Nuon firmware strings)

One interesting thing to note is that whoever bought this back in 2001 didn't actually buy it for the Nuon features. The rubber cover over the joystick ports is still there and if they had used a joystick the cover would have been removed and lost 110% guarantee since it's not a captive cover. Since the rubber cover is still there that proves they never used the joystick ports and never used it to play Nuon games.
The other interesting thing is if you look at the text in one of the images you'll see dozens of controller types that could potentially be recognised. This shows that the developers had big plans for the system (possibly too big hehe!), but sadly it wasn't fulfilled. Maybe with MAME emulation that will change :-)

19th May 2022
As usual I've been busy with lots of repairs. Here's a few unusual non-arcade repairs that were pretty interesting....

Colecovision Expansion Module#1
A local friend noticed a Colecovision Expansion Module#1 on ebay listed as not working and asked if I wanted it as payment for doing some repairs I was doing for him. I still have the Colecovision console I got as a kid back in the early 80's and the Expansion Module#1 would be a nice addition. I figured it can't be that hard to fix as there's not a lot to it so I said go ahead and grab it.
Colecovision Module#1 repair

If you're not aware of this thing, it was an Atari 2600 knock-off that Coleco did back in the day to cash in while the Atari 2600 was hot. It plugs into the front expansion bay on the Colecovision console and only used the power from the main Colecovision unit. Everything from the Expansion Module#1 was passed through to the RF output on the back and displayed on the TV. Even the joysticks were not shared, you had to plug in an Atari 2600 joystick into the front of the Expansion Module#1. It was the only front bay expansion made for the Colecovision so if you didn't have one then the front bay never got used. Well there was the Adam computer add-on, but we won't mention that because it was too expensive, wasn't done very well and was a commercial failure.
Of course when Coleco released the Expansion Module#1 stating it could play the existing library of 2600 games they were immediately sued by Atari but Coleco won because the Atari 2600 is made from all off-the-shelf parts, except the video chip. Coleco made their own video chip which wasn't pin compatible with the Atari 2600 video chip so they got away with it heh! In reality they still copied it even if it was done with off-the-shelf parts so they should have lost, but that's what you got in the early days where electronics was a new thing and law-makers didn't have a clue about this advanced technology LOL!

As expected inside there's just 3 chips like the Atari 2600. However unlike the 2600 the whole thing is a lot smaller and the video chip is a different custom part that isn't available at any price. Hopefully the video chip is still ok....
Colecovision Module#1 repair

Looking closely at it, it's clear it has been abused by someone and likely tossed out in their shed for 30+ years so it isn't in the best condition. Most of it looks fine but the CPU doesn't look too good....
Colecovision Module#1 repair

I first looked up the 6507 datasheet and then checked the clocks and reset on the CPU and they were both ok. I probed the CPU with my logic probe and it was dead, no activity at all on any pins. I didn't have a spare chip handy but I happened to have some Rockwell 6532 chips lying around so I swapped that chip but it didn't make any difference. The 6532 has a high possibility of failure because it contains the entire RAM for the Atari 2600. Yes, all the RAM is inside the 6532 RIOT chip... all 128 bytes of it. I don't know what dumbass designed this thing but whoever it was they should have thought about it for another 10 minutes then added at least 1kB or 2kB of RAM. Geez! The 2600 had a huge potential back then but was severely limited by the lack of RAM. Some of the things programmers were able to squeeze out of the 2600 were pretty amazing but we won't mention Pacman hehe!

The only other thing it could be is the CPU. This is a 6507, which is basically a 6502 with less address pins and less I/O. I pulled the chip and luckily the board isn't damaged and cleaned up pretty well....
Colecovision Module#1 repair Colecovision Module#1 repair

Looks like new :-D
I didn't have a spare, but I did have a couple of Atari 2600 consoles here so I borrowed the 6507, added a socket to the Coleco board and put the 6507 into the socket. I plugged in my 2600 Asteroids cart, powered on and got this....
Colecovision Module#1 repair

So yeah it was just a bad 6507 CPU LOL! I have ordered a couple of 6507 CPUs from two different online sellers and when they arrive (in about 6 weeks!) I will plug one in and the Expansion Module#1 should be fully working again :-)
The only thing left to do now is leave buyer feedback to the seller..... "Works great, thanks!" LOL!

Update 8th June 2022: The 4x 6507 CPUs arrived. These are made by UMC. I plugged one in and it works fine. I tested all the others and they work fine too!
Colecovision Module#1 repair Colecovision Module#1 repair

Cheapo Chinese joystick
About 2 years ago I picked up a cheap Chinese arcade-style joystick for use with my Playstation 1 and Playstation 2 for 20 Aussie dollars....
cheapo Chinese joystick upgrade

I never bothered to open it and I just used it, including on a PC with MAME. A couple of days ago I watched a review of this same joystick on youtube and then I remembered that the joystick in this thing is really crappy and wobbly. That got me thinking if the joystick could be upgraded to a nice Sanwa. I opened it up and had a look inside. I removed the cheapo joystick and sat a Sanwa joystick where the original one was. It didn't line up with the outer 4 holes but the middle 2 holes did line up. I screwed it in place and it fits but 4 screws would be better. Looking at them side by side they are very close. Maybe if I swap the metal plate that might be enough...

cheapo Chinese joystick upgrade cheapo Chinese joystick upgrade cheapo Chinese joystick upgrade cheapo Chinese joystick upgrade cheapo Chinese joystick upgrade cheapo Chinese joystick upgrade cheapo Chinese joystick upgrade

The metal plate lined up exactly and when the Sanwa joystick was screwed in place it fitted perfectly! I quickly wired it up. I knew which wire ground was because I had previously checked the wiring on the original joystick but the others were guessed. Of course it needed some adjustments but I got the white and blue wires correct LOL! Sanwa joysticks are wired (from left to right) up, down, left, right, ground. For reference the correct wire colors for this chinese box are (from left to right) white, green, yellow, red, blue. I re-wired it, tested using MAME and the test mode from an arcade game and the directions work correctly now.
cheapo Chinese joystick upgrade

I went to put the bottom back on and it didn't fit LOL! It's not much, maybe 2mm or something, plus the thickness of the bottom cover (~2mm). The chinese company who made this obviously didn't expect anyone to put a quality arcade stick inside. Ok, that's no problem for a Dremel hehe!
cheapo Chinese joystick upgrade cheapo Chinese joystick upgrade

Now it works perfect and sits on the desk fine. The buttons on this thing are rubber contact types so they don't have that annoying click sound which makes them really nice. Together with the Sanwa joystick this is now a very nice arcade stick for use with MAME and PS1, PS2 and PS3 :-)

Nintendo 64 PSU
Years ago I picked up a Nintendo 64 for use with dumping some of the ROMs that were used on some arcade games that used the same strange custom ROMs that were used in N64 carts. I also have one of those multi-carts so I play with it occasionally. Recently I noticed the N64 console was unstable and would reset after a minute or two of game play. I measured the power supply voltages and they were moving up and down. The N64 PSU is supposed to output 3.3V and 12V. The 3.3V was moving randomly from ~3.0V to 3.6V all over the place and the 12V measured about 11.6V but was also moving up and down. That's not right. I tried adjusting the pots but it didn't stop the voltage jumping. I also pulled and tested all the capacitors and they were ok. Not surprising really because they are quality Matsushita/Panasonic caps. The N64 PSU was manufactured by Matsushita and is massively over-engineered and is a very complicated and very compact switch-mode power supply. It's also 26 years old. Rather than jerk around with it and order parts that may not fix it, I ordered a knock-off replacement PSU from China for 20 Aussie dollars. When it arrived I powered it on and checked the voltages and they were rock solid 3.305V and 12.05V. Perfect! I plugged it into the N64 console and was able to play games just fine. The problem was the power cable that comes with the chinese PSU is not very long and the special power connector that plugs into the N64 doesn't fit well either, plus the whole PSU unit doesn't click nicely into the back of the N64 console like the original does. You sort of have to jiggle it and eventually it goes in. Now I was wondering if I could do a case and cable/connector swap. Hmmm....
I pulled the thing apart but the board didn't want to come out....
Nintendo 64 PSU replacement / retro-fit

Inside there are 2 curious blobs of goop. I wonder what's under them....
Nintendo 64 PSU replacement / retro-fit

Screws LOL! Ok so I removed those hidden screws and then it came out. It's a pretty simple design and would be very easy to repair if it failed in the future.
The voltages on the connector are like this....
Nintendo 64 PSU replacement / retro-fit

The original PSU has a flat cable with 5 wires....
Nintendo 64 PSU replacement / retro-fit

The chinese copy has only 3 wires.... urggh! At least they were nice enough to mark the voltages on the board....
Nintendo 64 PSU replacement / retro-fit

If you're a chinese N64 PSU bootlegger reading this, please modify the design and add 5 holes in the same order as the original so we can easily swap everything over without having to re-route wires! It's not that hard!
But ok no problem. I marked the wires so I'm 100% sure which wires are which. Then separated the wires and routed them to the correct place. I poked both of the ground wires into the ground hole, both of the 3.3V wires into the 3.3V hole and the 12V wire into the 12V hole then soldered them in place. I also transfered over the original AC cable then put the board back into the original case. It fits perfect!
Nintendo 64 PSU replacement / retro-fit Nintendo 64 PSU replacement / retro-fit Nintendo 64 PSU replacement / retro-fit

The little screw holes in the PSU board can't be used because the original N64 PSU case didn't use any screws to hold the board in place. I closed up the case and it snapped shut nicely and doesn't rattle. I was about to screw the case together using the original Nintendo security screws but I really hate those silly star head screws so I used the chinese philips screws which fit well and tightened up fully. I pushed the PSU into the back of the N64 and that clicked into place nicely too. Then powered on and tested it using my Goldeneye cart that has a Mario 64 label hehe! Works perfect! :-)
Nintendo 64 PSU replacement / retro-fit Nintendo 64 PSU replacement / retro-fit Nintendo 64 PSU replacement / retro-fit Nintendo 64 PSU replacement / retro-fit Nintendo 64 PSU replacement / retro-fit

21st February 2022
Continuing on with the TMNT repair, powering on with a good PSU shows the Z80 is active but no sound plays. Or so I initially thought. The in-game attract mode sound plays! If I start a game there's sound but no title theme music. So we still have a fault in the sound section somewhere.
btw, I forgot to mention yesterday, before replacing the bad 74LS04 at D8, I could get the Z80 to become active by removing the RAM next to the Z80. The Z80 wasn't running code obviously, but all the pins were active and it was waiting for something. Yeah, probably waiting for me to fix it LOL! Anyway I just thought that was a little bit strange. It looks like because the YM2151 was not running due to the missing clock, the YM brought down the whole sound system including the Z80!
Anyway, this is what the 74LS04 pin 8 and YM2151 clock looks like now. It's about the same as the Z80 clock was before changing out the LS04, just not as wiggly at the bottom. So yeah, just remember wiggles are bad.
TMNT repair

Checking the MAME tmnt source code shows that the chip responsible for playing the title theme is the uPD7759. Referring to the VOICE schematic page posted yesterday....
TMNT repair
and upper left quarter of the board....
TMNT repair

The uPD7759 is located at D16. The 640kHz clock (the little square blue thing just above the uPD7759) is present on pin 23. Reset is on pin 19 which comes from a 74LS74 at E10 pin 5 and that is also present and working.
To try to speed this up a bit, rather than randomly checking chips in this area let's try to cheat and have a quick look at every chip on the VOICE schematic page, make a list and see if any are Fujitsu chips. Then we will have a fixed target to aim at ;-)
Note: The entire left section of the VOICE schematic can be ignored because that's for use with 32 pin EPROMs. This game uses a single 40 pin MASK ROM in the same location.
4069 at F8 (not Fujitsu)
74LS74 at E10, H9 (Fujitsu)
74LS161 at D9 (Fujitsu)
74LS393 at C7, D7, E7 (all Fujitsu)
74LS32 at G9. Hmmm no chip at G9! But there's a 32 at F9 so that must be it!
74LS04 at D8 (already replaced so must be good)
74LS273 at F15, B16 (not Fujitsu)
4Mbit MASK ROM at D5 (Fujitsu)
74LS166 at E7, E8 (Fujitsu)
1Mbit MASK ROM at D18 (Fujitsu)
YM3014 at D10 (not Fujitsu)

OK, so looking at the MAME source code shows exactly which ROM contains the title song....
MAME tmnt.cpp source
ROM_REGION( 0x80000, "title", 0 ) /* 512k for the title music sample */
ROM_LOAD( "963a25.d5", 0x00000, 0x80000, CRC(fca078c7) SHA1(3e1124d72c9db4cb11d8de6c44b7aeca967f44e1) )
This means I can ignore the other ROM at D18. Let's assume that the ROM at D5 is good. I can also ignore all non-Fujitsu chips.

Starting in the top left corner of the schematic, the 74LS74 at E10 has active outputs on pins 8 and 9. Pin 9 is tied to CK input pin 2 of the 74LS161 at D9. Output pin 15 of the LS161 is active and tied to pin 13 of the LS04 at D8 and the output pin 12 is active and must be good since we already changed that chip. There's another active output from the LS161 on pin 11, tied to pin 1 of a 74LS32 at G9. The output is pin 3 and there's an active signal there too so the LS32 is also working. The 74LS74 at H9 is tied into the system reset signal on pin 1. Input pin 2 is tied to the Z80 databus D2 and is active. Input pin 3 is high but toggles low briefly at the title theme intro screen. Output pin 6 is high but when pin 3 briefly toggles low, at the same time output pin 6 goes low and stays there for a while. This is obviously the same period when the title theme is supposed to play because after about 15 seconds pin 6 goes back to high. This means the 74LS74 at H9 is also working.
So I can cross off D8, D9, G9, H9 and E10 as they all appear to be working.
That leaves the 3x 74LS393's and the 2x 74LS166's. Hmmm ok so this is getting very do-able now :-)
Let's look at the 74LS393 datasheet to see how it works....
TMNT repair TMNT repair

This chip is a Dual 4-bit Decade and Binary Counter. 'Dual' meaning there are 2 separate circuits in the chip. The datasheet truth table shows COUNT and 4 outputs. This doesn't match with the chip because the chip has input pins 1A and 2A, and also two CLR pins. On all 3x 393's the CLR pins are tied together so no need to worry about those. From previous checking we already know that this CLR signal comes from the 74LS74 at H9 pin 6 and is low when active (when the title theme plays). The 1A and 2A pins appear to be the COUNT signal shown on the truth table. I'm not even sure I know how to check the count signal but it actually doesn't matter. The pin 1 input (1A) comes from the LS32 at G9 pin 3 which is working. The other 1A and 2A inputs come from these same chips fed from the outputs and chip E7 only uses 1A. The schematic shows that the outputs from the 393's connect to the address bus A0-A17 (18 address bits total) on the ROM at D5 so these chips are selecting the ROM address. Two of the outputs from C7 and D7 also connect back to another LS393 input. The inputs on all 3x 393's (1A, 2A) are active. It appears E7 is the final output which has five unused output pins and three used pins. Two of the used pins are tied to the ROM address lines (A16, A17) and the remaining used output connects to the LS32 at G9 and both 74LS166's. The 74LS393 output pins for C7 and D7 (2x pins 3, 4, 5, 6, 8, 9, 10, 11) are all active. The 74LS393 at E7 uses only output pins 3, 4 and 5 (the others are no-connect). Pin 3 has no signal at all (not high, not low), pins 4 and 5 are static lows. I piggybacked a working 74LS393 over the top of E7 and now pin 3 and 4 are active when the title theme is supposed to play, but I still can't hear the theme tune playing. I pulled and replaced the 393 anyway as it looks to be bad....
TMNT repair TMNT repair TMNT repair

I tested the old 393 in my chip tester and it fails. The display shows pin 3 is low but a high was expected....
TMNT repair

Moving onto the 166's, let's first have a look at the datasheet for this chip....
TMNT repair

This chip is a Parallel-Load 8-bit Shift Register. There's only 1 output (pin 13). The inputs (pins 2, 3, 4, 5 10,11, 12, 13, datasheet labels A, B, C, D, E, F, G, H) are tied to the ROM databus and are all active. The other inputs are tied to existing signals I've previously checked. The output pin 13 on the 74LS166 at E7 goes to the other 74LS166 at E8 into pin 1 (SERIAL). At the point before and during the title music playing, pin 13 of E7 looks like this....
Before: TMNT repair During: TMNT repair

Similarly pin 13 of E8 looks like this....
Before: TMNT repair During: TMNT repair

This is where a CRO can be over-rated because I have no idea what it's supposed to look like. To me it looks like both chips are working since the waveform changes when the theme song starts to play and goes back to the same as before when the theme stops and the waveform is not complete garbage. But E8 seems to have less activity so maybe it's suspect. Additionally the signals sound and look ok with my logic probe. I piggybacked a working LS166 over E7 and it didn't affect anything. I piggybacked a working chip over E8 and I can hear the theme song playing! It's really scratchy and rough but I can definitely identify it as the TMNT theme song. So I suppose E8 is bad. I changed it for a working chip....
TMNT repair TMNT repair TMNT repair

I tested the old 166 in my chip tester and it fails. The display shows pin 13 is low but a high was expected....
TMNT repair

After changing the chip, I powered on expecting the theme tune to play perfectly but it's exactly the same as when I piggybacked the LS166 on top of the bad chip! Looks like we have a fault further down the line, maybe in the analog opamp section.
I'm kind of running out of time and patience now. I pulled a bunch of the remaining Fujitsu chips and some others in this same area... the YM3014, the other two Fujitsu 74LS393's, the other Fujitsu 74LS166 and the LM358 at C10. I tested the LM358 and YM3014 on a different board and they are fine. I tested the pulled logic chips in my chip tester and they pass. I pulled and read the ROM at D5 and it matches MAME archives. Just to be sure I replaced it with an EPROM but that didn't make any difference. I replaced the pulled Fujitsu chips with good chips (never put Fujitsu chips back on a board even if they test good!!) and put everything back and it may be fixed. I'm not sure. The theme tune plays fine with the volume on a normal level. But when turned up to full volume it sounds like it's clipping. But this is definitely an improvement so at least one of the chips I just replaced was marginal but not showing up on the CRO or logic probe or chip tester! It sounds pretty good now as long as the volume is not set at maximum. In reality no one is going to put the volume up full anyway so it's probably good enough to call it fixed ;-)
There are some opamps further down the line (2x LM324 and another LM358) but if they were bad then all the sounds would be bad and it's only the theme tune that sounds clipped at full volume. I suspect it's not right but I don't have another board to compare against. It could be some caps I suppose. The owner has another board so I've asked him to check it and get back to me. It sounds ok at normal volume so even if it's not correct it probably doesn't matter.
Update 22nd Feb: The owner said at full volume the theme tune is distorted on his other working board exactly like I described. So this seems to be a common issue with TMNT! So the sound issue is 100% fixed :-)

It's time to go back and have a look at that red 'Scene 1' screen.
I figured this fault is probably in the color section of the schematic....
TMNT repair

The color RAM at F22 and F23 must be good otherwise there would be huge color issues. Anyway, the color RAM is tested at boot-up and passes so must be ok. If I narrow it down to just Fujitsu chips, there's not many... the 4x 74LS07 at D23, E20, D20 and D22, 3x 74LS157 at D25, E25, G25 and the 74LS32 at H21. I checked the 07's and 157's with the logic probe (all ok) and also piggybacked chips over the top and there was no change on screen at the 'Scene 1' screen. I checked the outputs on the 74LS32 and pin 8 is a static high. The input pins 9 and 10 are active so this chip is bad. I piggybacked a good chip on top and now the 'Scene 1' screen is black like it should be. I pulled and replaced it....
TMNT repair TMNT repair TMNT repair TMNT repair

Strangely the known bad Fujitsu 74LS32 tests ok in my chip tester and also in my EPROM programmer logic test function.

The final minor issue is a broken cap. This doesn't actually do anything and before starting the repair I just snapped it off for the entire repair and everything was fine. If you see this kind of thing on a board, DON'T just push it back on. It can cause a short and on a 12V cap that would be very bad ;-)
This cap is C20 shown on the SND schematic page near the main power AMP at location J1. It just sits between 12V and ground. I've replaced it with a new one. I may change out the remaining caps later if necessary. One last thing is there's some sort of, erm, white crap on the OBJ ROMs. Not sure why, but looks like some TMNT fan boy got a bit too excited and shot his load on there LOL! It's all cleaned up now :-)
TMNT repair TMNT repair TMNT repair TMNT repair

Here's the final 'summary shot of shame'. Don't look too closely, this can give you nightmares for days! ;-)
TMNT repair... dead Fujitsu chips

For now all the faults are fixed so that's the end of this TMNT repair log. I may change out the remaining Fujitsu logic chips just to make sure it doesn't fail again. But that will be done another day. I'll ask the owner what he wants to do about that. The relentless summer heat is erm, relentless (hehe!) so now it's time to relax with a lemon, lime and bitters and recover for a while!

20th February 2022
A local friend asked me to look at a Teenage Mutant Ninja Turtles (TMNT) board that he picked up as a spare some time ago. It was working with a minor graphics fault and there was no sound at all.
I forgot to take a pic of the board before I started so here's a 'stock' picture hehe! The board I have will be shown a bit later once the repair starts. Anyway it's just a common TMNT board, nothing unusual.
TMNT repair

The particular board I have is a very nice example because there's no corrosion damage and no cowboys have butchered the crap out of it. No one has touched it before, which is quite rare these days. There were no boot-up errors so most of the board seems to be fine. This is very unusual because these boards have dozens of Fujitsu logic chips and there has to be several of them dead or failing. That's almost a guarantee!
I first flicked on the test DIP switch to check the MASK ROM test. I powered on and the game came up as usual... no test mode!
I started probing around the DIP switch area then suddenly I got this.... (!)
TMNT repair

Whoops! Something just failed and now there's only a bunch of wiggly crap on screen LOL!
Looks like there's no sync signal. Fortunately the full schematics are available. Even better I own the original paper manual with the schematics.
For this log I will be using the good-enough poorly scanned schematics that are available online. But don't worry, I will fix this problem later ;-)
I had a quick look to see where the sync signal is coming from....
TMNT repair TMNT repair

The first image shows the sync signal on JAMMA pin 13 and it comes from a signal called 'SYNC' with page reference IOE3. The 2nd page shows part of the IO page and the SYNC signal comes out of pin 5 of a 74LS244 at location D27. Looking at the board, this is our unfriendly Fujitsu branded logic chip. Probing the sync input (pin 15) shows a normal sync signal and probing the output (pin 5) shows a static high so the sync is not coming out. Additionally, the 4-position DIP switch is also connected to this chip and DIP switch #3 is the test mode switch so that explains why the test mode doesn't work. I replaced the 74LS244 with a working chip and now the board is back to normal, or at least as normal as a partially working TMNT board can be heh! I tested the bad 74LS244 in my chip tester and it shows that the chip is partially working but pins 5 and 16 are stuck high.... pin 5 is the sync output and pin 16 is the output for input pin 4 which is the signal coming from DIPSW3 switch #3 :-)
TMNT repair

I flicked the test DIP switch on, powered the board on and got this....
TMNT repair, 74LS244 at D27 replaced with working chip TMNT repair

OK, so now the board is booted, this shows the minor graphical glitches that the owner mentioned and the test mode says ROMs K6, H6 and K27 are bad. They might actually not be bad. All this means is the board is not getting back the right data when it calculates the checksum. I looked at the schems and these ROMs are listed on the VRAM and OBJ pages....
TMNT repair TMNT repair

Let's look at K27 first. This ROM has a long indented line across the length of the ROM. That's a sign that it's a Fujitsu ROM. These ROMs are also failing a lot nowadays, especially on 90's Sega boards. The schematic shows K27 is connected to the custom chip 052109 and the MASK ROM at H27 and nothing else of significance (CN5 is the expansion connector which is not used). I beeped out all the pins of K27 to H27 and to the custom chip and everything is connected. I also checked every pin on all the large square custom chips to make sure all of them were properly soldered down and they were all good. The only option remaining is to pull the ROM and read it in an EPROM programmer to see if it matches the known good archives from MAME. The ROM doesn't match so I replaced it with a AM27C400 EPROM....
TMNT repair TMNT repair, MASK ROM at 27K repaced with EPROM TMNT repair, MASK ROM at 27K repaced with EPROM

Yup! That fixed the error on K27. Now there are only two bad ROMs remaining. I beeped out the connections on the ROMs at H6 and K6 and checked for loose legs on the custom chips and everything was connected as per the schematic. I pulled and read these ROMs but they tested ok. This is not surprising because these other ROMs are made by Sharp and are (currently) not known for failing. Just to be sure I put sockets in place and replaced them with EPROMs but it didn't make any difference, those ROMs still fail. The game plays perfect with no graphical issues so I can only assume that the data isn't getting back to the CPU and it thinks they are bad. The only extremely minor issue I see comparing to MAME is in MAME the 'Scene 1' screen is black and on this board that screen is red. I may come back to this issue later. It's probably just another bad Fujitsu logic chip somewhere. For now it doesn't matter so I'm going to move on.
TMNT repair TMNT repair TMNT repair TMNT repair

The sound issue is next. Let's have a look at the schematic first. There's two pages, one for the Z80 and YM2151 and one for the uPD7759 sample player chip....
TMNT repair TMNT repair

I first checked that the Z80 has a clock signal on pin 6 and reset signal on pin 26. They were both present and correct when I probed them with my logic probe. I powered the board off then on while probing the Z80 address lines and the Z80 runs for about 1 second then quits, meaning it was trying to run code but has crashed. I piggybacked the RAM at location F16 (which is a Fujitsu RAM) but believe it or not this Fujitsu RAM is actually reliable! Piggybacking didn't help so I pulled the RAM and tested it in my chip tester but it passed. I added a socket and replaced it with a known good chip but the Z80 was still not running code. I pulled and tested the sound program ROM at location G13 but it matches MAME archives. The schematic shows the Z80 clock comes from the 3.58MHz oscillator at location G10. The clock goes into a 74LS04 at location D8 on pin 1 and comes out on pin 2. That 74LS04 is a Fujitsu logic chip but the Z80 has an active clock and appears to be ok so the chip appears to be working. I even measured the clock with my frequency counter and it comes out on pin 2 exactly correct so the 74LS04 appears to be working even though it's a Fujitsu chip....
TMNT repair, good Z80 clock

Probing the clock signals with my logic probe again, on pin 1 the probe makes a normal beep sound and the orange LED is flashing to show there's a clock signal present. Probing pin 2 of the 74LS04 (output) also gave a flashing clock signal on my logic probe. The schematic shows the same 3.58MHz clock goes to the same 74LS04 into pin 9 and out on pin 8 then to the YM2151 pin 24 clock input pin. I probed pin 9 and got a normal clock signal. On pin 8 it was a static low. I measured the clock on pin 8 with my frequency counter and it came out exactly the same as the frequency counter image shown above so the clock is good, right? Hmmm, well I'm not happy that the signal is only low on my logic probe. Maybe it's time to break out the CRO! I probed pin 1 of the 74LS04 and got a waveform that looks a little bit wonky but I assume must be ok since it's coming directly from the oscillator. On pin 2 it's similar, but again probably ok since the Z80 was trying to run code. I then moved onto checking the other pins 8 & 9. Probing pin 9 shows the same clock waveform but on pin 8 (the output) it shows a straight line low signal at about 1 volt. Hmmm, could this chip actually be bad?
TMNT repair, good clock on pin 1 of 74LS04 at D8 TMNT repair, good clock on pin 2 of 74LS04 at D8 TMNT repair, YM2151 clock coming out of 74LS04 pin 8.... bad!

I pulled the chip and tested it in my chip tester and it passed! So the chip is good enough to pass the 3.58MHz clock as a frequency but not good enough to pass the correct waveform. Anyway, I replaced the chip with a good one....
TMNT repair TMNT repair

I powered on expecting there to be an improvement and all I got was a flash on the screen and then BAM! Nothing. The whole board was dead. Nothing on screen. WTF? I looked at my power supply and the power LED is not on. Errr. Looks like the PSU has just blown LOL! I have plenty of spare PSUs here but in the spirit of learning I'll have a quick look and hopefully it's a quick fix!
I opened the PSU and found the fuse is blown and there's a short to ground on the 12V output. The other power rails were not shorted. This type of arcade switching power supply uses an old-school TL494 chip as the switching controller and are pretty simple and relatively easy to fix as long as you keep spare parts.... and I do. At least for the type I like to use, either Peter Chou or
the more modern and still manufactured WEI-YA WY-03CM, which is essentially a Peter Chou copy. Don't be fooled into thinking that the expensive Suzohapp PSUs are any better. They are exactly the same WEI-YA PSUs just rebranded ;-)
Easiest way to diagnose this kind of fault is just start removing parts in the 12V section until the short goes away. I pulled a few electrolytic caps and tested them but they tested ok. I also pulled the double diode 3-pin IC (looks a bit like a big transistor) but that also tested ok with my MG328 component tester. I used my multimeter in beep mode to check parts for a short and when I checked the two big beefy diodes at D21 and D22 (marked '30DF2') they were both shorted to ground on both sides. I pulled both and tested them and one tested ok but the other was shorted. I replaced it with a similar diode (600V 3A Fast Rectifier) and tested the resistance across the diode again and it was about 200 ohms. I replaced the fuse, put it all back together, powered on and the power supply came back to life. Ok so that didn't take too long to fix it, about 1 hour :-)
TMNT repair TMNT repair TMNT repair TMNT repair TMNT repair

Unfortunately I've run out of time today so I will continue the TMNT repair tomorrow.

14th February 2022
A couple of weeks ago a local friend picked up a neglected Galaxian bootleg (short style) board. He dropped it off here a few days ago and today is fixin' day. It was showing random garbage on screen...
Galaxian repair Galaxian repair Galaxian repair

I first checked the ROMs and found that some identified as the 'redufob2' set in MAME but a few of them were unknown. One ROM had a missing leg so I soldered on a new leg and then dumped all the ROMs and plugged them into MAME. The game worked perfectly so I knew the ROMs were ok. This set has been added to MAME as 'redufob3'. A tip for patching chip legs..... after soldering, sand off most of the solder blob and the patched leg will look nicer :-)
Galaxian repair

Moving on, I pulled off the ROM board and noticed the legs underneath were corroded so I sanded the legs with fine sandpaper and plugged it back in. At power-on the game was still showing random garbage, but moving almost like the normal Galaxian boot-up. Probing the ROMs with my logic probe showed the code was running and just before resetting it was showing some text but it was very difficult to read. It was showing BAD RAM x where the x was a number but not readable. There is a Galaxian test ROM available so I programmed the code to an EPROM, ran it in ROM location #1 and it came up with a message...
Galaxian repair Galaxian repair Galaxian repair

I was going to start worrying but the message assured me I shouldn't worry LOL! That's a relief! Problem is this error isn't 100% crystal clear. Despite the fact that the test code is for a 2716 (2kB) EPROM and about half of the ROM is empty (i.e. plenty of room for say... ummm, a proper bad RAM location maybe??), whoever wrote the test code wanted to assure me to not worry by wasting several bytes on a pointless 'worry' message but wasn't able to come up with a better way to provide any more useful info about the exact location of this 'stuffed' RAM. Here's a pro tip.... remove the 'worry' message and re-use those bytes to give the RAM locations.
After some research I found out that ORAM is the object RAM located at 4F and 5F on the bottom board. These are 2x M5L2101 256x4-bit SRAMs and were commonly used in late 70's arcade PCBs including Bally MPU pinball boards and also used in the RCA Studio II game console and the clones Victory MPT-02 and Mustang 9016 Telespiele. I know this because I recently looked at the Victory MPT-02 and Mustang 9016 consoles I have here, dumped all the carts I had access to and updated the Studio II hash file in MAME with some proper documentation and added all homebrew games, as well as repairing both consoles to get them working. Those same RAMs are possibly used in several other things too. I pulled both chips and tested them in my IC tester. One passed and the other failed. I have a few spare chips here so I put back the good chip and replaced the bad one with a good chip. I put back the original ROM, powered on and expected the error to be gone but I got this....
Galaxian repair Galaxian repair Galaxian repair

It's the same error but the moving start-up test garbage is now the correct color. Hmmm.
I re-tested with the test ROM and it still showed 'ORAM STUFFED'. I tested both RAMs again and they both passed. Just for curiosity I replaced the other RAM that previously passed with a different RAM and got this...
Galaxian repair Galaxian repair

Ok so the game is working now. I tested it and it appeared to be ok, including sound.
I played the game for a while and noticed that the explosion/death sound didn't play at all. There is a very nice 2-part troubleshooting manual available that was put out by Midway back in the day. If you have a Galaxian PCB (including the bootlegs which are a 1:1 copy) and it has issues you should definitely check it out. The manual is available in many places on the net, for example here
Galaxian repair

There is a section on the sound and it gives some info about things to test specifically for a 'Bad Explosion' problem....
Galaxian repair Galaxian repair

After going through the troubleshooting steps listed in the 'bad explosion' text, everything checked out ok. While probing pin 7 of IC9L and diode D1 I could see the explosion sound signal showing up as activity on my logic probe, so the sound was definitely being made but it wasn't coming out of the speaker. Obviously a part on the output side was faulty. I pulled up the schematic and traced the explosion signal from the 74LS259 at IC9L to the amp chip and speaker output...
Galaxian repair

If you follow the red line you will see the 'hit' signal goes through a 1K resistor at R89, 4148 diode at D1, 4066 at 7R, 150K resistor at R35, cap C23 and into pin 2 on the LM324 at 7T. The LM324 is the first suspect. The hit signal goes in on pin 2 and the fire signal goes in on pin 5. The fire sound was working so the LM324 should be ok but it's possible just part of it has failed since a LM324 is a common failed part. I piggybacked the LM324 with a good working part but the explosion sound was still not heard. Additionally I probed the input (pin 2) and no signal was present so it's not even getting to the LM324. Working backwards, the troubleshooting info said to test the sound on R89 and D1 and it was present there. I also checked it on pin 4 of the 4066 (input) and it was also present, although strangely the repair info didn't mention this in the 'bad explosion' section, nor to check the output heh! They did mention it on the 2nd page but not specifically relating to the explosion sound. The output is pin 3 and on my probe it was silent! I piggybacked the 4066....
Galaxian repair Galaxian repair

Yep that fixed it! I pulled and replaced the 4066 and that fully fixed the sound issues.
Galaxian repair Galaxian repair Galaxian repair

The first pic doesn't show it, but when it came in the board was pretty rough and dirty and only had a piece of cardboard between the PCBs. No feet, no spacers, no screws. I found some and went to fit them but discovered an issue with the PCB...
Galaxian repair Galaxian repair

With the front screws in place there's no holes for the spacers at the back of the board near the joining cables! WTF??
If I move the board to the back to use the rear holes there's no matching hole on the bottom board and the top board holes would line up with traces on the bottom board so a hole can't be put there. I suppose it's time to drill some D.I.Y. holes at the back heh!
Galaxian repair Galaxian repair

I checked a different near identical board here and it looks like someone did exactly the same thing with that board many years ago so it looks like a common issue hehe! Ok so now it has 4 spacers, 4 screws and 4 feet fitted and is back to normal heh!

3rd February 2022
As always I've been busy with lots of repairs. Here's a few that were done recently.

Snow Bros.
This one is fairly easy. The screen flickers quickly. When looking through a camera half the screen is good and half the screen is bad. This is a known issue... at least to me ;-)
One of the 4464 video DRAMs is bad. Fairly easy to find the right one by simply piggybacking a chip over the top.
After a quick chip change it's working again.
Snow Bros. repair Snow Bros. repair Snow Bros. repair Snow Bros. repair Snow Bros. repair Snow Bros. repair Snow Bros. repair

Truxton / Tatsujin
Just shows an error on bootup. The board is not in great condition and there's no schematics available. Mission Impossible!
Truxton / Tatsujin repair Truxton / Tatsujin repair

I have no idea what L-UP means, but the number shown is 01447fe. Now if you check the MAME source for Truxton you will see something interesting.....
Truxton / Tatsujin repair

You'll be surprised what you find in the source code of MAME. Always look for big red arrows in the source! ;-)
The source shows the memory map and that number is in the range of the bgpalette (background palette). The full range is 0x800h bytes, or 2kB. There's another one shown below it with range 146000 - 1467ff (another 2kB).
Now which chip is 2kB and is for the color RAM? There are several 2kB RAMs on the board so actually I have no idea. Piggybacking a 6116 RAM on all of them had no effect, but shorting out the data lines on two of them affected the colors. I did not know which one was the bad chip so I just pulled one of them, tested it in my chip tester and got lucky!
Truxton / Tatsujin repair Truxton / Tatsujin repair

Now the game boots up. Clearly this was the original fault from back years ago before it developed this fault and was then abused and tossed around in some losers shed.
It's not obvious from the pics here but there are lines through the sprites. There's always something else! :-/
Truxton / Tatsujin repair Truxton / Tatsujin repair Truxton / Tatsujin repair

On this board the sprite ROMs are labelled B65 01, 02, 03 & 04
First I pulled and read all those ROMs and they matched MAME archives so all ROMs are good. I probed the pins of all these ROMs with my logic probe and noticed pin 10 was dead with no activity on all 4 ROMs! These ROMs are 1Mbit 28 pin mask ROMs and not directly replaceable with common EPROMs without modifications to the PCB so hopefully it's just a bad connection. That pin is A0. I scratched the nearby traces and tried to get a continuity reading but I couldn't get a beep for A0 or A1 from any visible traces. Time to pull some chips! As expected, there's a broken trace right next to the hole for pin 10 so A0 wasn't being driven. I patched the trace and replaced the crappy socket and that should be it, right?
Truxton / Tatsujin repair Truxton / Tatsujin repair Truxton / Tatsujin repair Truxton / Tatsujin repair Truxton / Tatsujin repair

Actually no! It didn't make any difference!!!
WOW! Another fault? (cue Mission Impossible music....)
Well the next step might be the bank of 2148 SRAMs. They are all running really hot and one or more might be bad. I piggybacked them all but it didn't really make much of a difference. I probed the RAM inputs and a couple of them looked wierd. I traced those inputs to a couple of 74LS373 logic chips and noticed some more water damage nearby so I pulled them.....
Truxton / Tatsujin repair Truxton / Tatsujin repair Truxton / Tatsujin repair Truxton / Tatsujin repair

Yup! More broken traces caused by water! I patched the trace, replaced the logic chips and it was finally fixed!
Sadly this board will probably develop another fault eventually because of the poor condition.
To avoid that keep your boards clean and dry people!
Truxton / Tatsujin repair Truxton / Tatsujin repair Truxton / Tatsujin repair - good sprites now

Tiger Road
This is a bootleg, but has a nearly identical layout to the original and without any (nasty) custom chips.
Boots up and shows an error 'WORK RAM : NO GOOD'
Tiger Road repair Tiger Road repair Tiger Road repair

The work RAM on any arcade PCB is always the RAM connected to the main program ROMs. On this board it is 2x TMM2063 SRAMs. I changed one of them and now it passes all the RAM tests buts gets stuck on another screen....
Tiger Road repair Tiger Road repair Tiger Road repair

The other work RAM is the same type TMM2063 which is a known issue on many PCBs, so I changed that one too and now it boots!
Tiger Road repair Tiger Road repair Tiger Road repair

The colors are not right. There's some sort of red in the background, but the main red is missing. On this board the colors go through 2x 6116 color RAMs then 3x 74LS367 logic chips then out through 5 resistors (a set of 5 for each color) that have been shoddily soldered together. I piggybacked the top 6116 at IC165 but it didn't make any difference. I pulled and tested it but it was ok. I piggybacked a 74LS367 logic chip over the top and when held just right the colors came up good. The border was still red but that warranted pulling and testing the chip but it tested ok.
Tiger Road repair Tiger Road repair Tiger Road repair

Maybe there's a broken trace somewhere. I made a really quick and dirty schematic of how the chip is wired. 4 pins go to the RAM and 5 pins go to the resistors. The resistors are (from right to left) 4.7k, 2.2k, 1k, 470, 220. That all checked out ok so no broken traces there.
Tiger Road repair

Maybe there is a broken resistor. Since they are all soldered together it's difficult to see so I pulled and tested the resistors. When I desoldered the 5 resistors from the PCB the first one separated by itself and fell off! If you look really closely at this pic you can just see the dry joint on the first resistor!
Tiger Road repair

I resoldered the resistors and that fixed the issue with the colors.
Tiger Road repair Tiger Road repair Tiger Road repair

I played the game and some sounds were missing. I checked the sound section and a couple of caps were broken so I replaced them, reflowed and straightened all the others in that same area and that fixed the sound.
Tiger Road repair Tiger Road repair Tiger Road repair

Now for something completely different!
A local friend gave me a Namco Guncon-45 Playstation light gun as payment for fixing some of his stuff....
Namco Guncon-45 repair

It doesn't work but it can't be that difficult to repair, right? ;-)
When testing it with Point Blank the game shows the calibration screen but aiming and pulling the trigger does not advance to the next screen where it shows the cross-hair and you can move it around on the screen. Pulling the trigger does nothing and it just keeps asking to aim in the middle of the screen and pull the trigger. The shot sound is made so the trigger is working. Inside is a small board with a small number of components. Looks like a relatively simple microcontroller and a light sensor with a lens to focus the light onto the sensor. The easiest thing to start with is to check the cable. I beeped out the connections from the Playstation end of the cable to the gun PCB end of the cable and found 2 wires (pin 3 and pin 8) not connected. I did not know if those wires were supposed to be unconnected or not. Looking up some info on the net suggested the 2 pins were supposed to be unconnected but I did not have another Guncon-45 to compare against but it seems plausible that they are correct because pin 3 is 7.2V for a feedback motor and pin 8 is listed as unknown so likely not connected either.
Namco Guncon-45 repair Namco Guncon-45 repair Namco Guncon-45 repair Namco Guncon-45 repair Namco Guncon-45 repair

The next step is going to require swapping a few parts I think, but I have to consider the best way. The most obvious route seems to suggest the sensor might be suspect. I looked inside my Namco Time Crisis arcade gun and noticed that the sensor looked exactly the same. This gun is very simple and is only a sensor on a small PCB, a connector with 3 pins and no other parts. The sensor also has 3 pins so it's a 1:1 connection. The board for Namco arcade guns with the sensor and connector is available to buy new but the price is ridiculous... it's 2 bucks worth of parts for $66! I didn't feel like bending over to get a rectal examination today so I took a chance that it might be identical. I desoldered the sensor from the Guncon and swapped that into the Namco arcade gun, tested it with my Point Blank arcade PCB and it worked so that proves the sensor is ok. The actual sensor seems to be completely unknown so just for kicks I researched it for a few days and eventually figured out what it was and ordered some spares. When they arrived I swapped in a spare sensor into the arcade gun, tested with Point Blank arcade again and it works so looks like I might have to make some re-productions of the little sensor board used in Point Blank, Time Crisis 1 and Time Crisis II guns to thwart the rip-off merchants hehe!
Namco Guncon-45 repair Namco Guncon-45 repair

On the Guncon control board there are many other small SMD parts (resistors/caps). I measured the resistance of every SMD resistor on the board one by one and they all checked out ok. It's more difficult to measure SMD caps in-circuit so I removed every SMD cap one by one and tested them in my MG328 component tester and they all tested good. On the back of the board is an 8MHz crystal. I tested that with my frequency counter and found that it measured correctly so it must be ok.
Namco Guncon-45 repair Namco Guncon-45 repair

On the board there's another small SOIC8 chip. This is a BA7071. It's a sync separator and if it's not working that would cause the gun to not register hits. I did not have any chips in stock so I ordered 5 for 2 bucks from China and they arrived about 1 month later. I swapped in the sync chip and expected it to be working but it still didn't work! The funny thing is when I used IPA to clean off the flux the writing on the chip came off! Hmmm, maybe the chip is fake. I compared one of the other chips and they look legitimate enough with the same package and round intent and I don't see the Chinese rebadging a chip worth 20c so it might be ok but I have no way to test it. Now I'm kind of screwed because I have no more options to try.
Namco Guncon-45 repair Namco Guncon-45 repair Namco Guncon-45 repair Namco Guncon-45 repair

So what do you do when you have no other options? Well you go out and buy a mint new-in-box Japanese Namco Guncon-45 for spare parts, that's what you do!
Namco Guncon-45 repair Namco Guncon-45 repair Namco Guncon-45 repair

It wasn't that bad, only 60 aussie dollars and I've been wanting one for a while anyway. I'm sure it's less than they were when new. This one is working fine and has none of the silly orange crap stickers like they do here in Australia. This is a proper gun that you can use to hold up a bank, or at least that is what losers in the government believe because over here you can only get bright orange, red or blue arcade/console guns. It seems that in Japan people are smart enough to know that a plastic gun with a 3 foot cable hanging out the back doesn't make a good bank hold-up weapon, but here in Australia Aussies are not too smart and would probably try it so the guns are all bright colors so we can't hold up banks! But the government losers forgot about paint. Never underestimate a can of black paint since it can mask an orange plastic gun and make it look like a real one then bam(!) it becomes an instant bank hold-up gun! Nevermind that the barrel is blocked off and has a plastic clear lens at the end of it. It's black so it must be real! This same problem also affects the new pc-based made-for-MAME Sinden Light Gun coming from the UK. But even worse, customs people 'confiscate' them because they are a 'dangerous weapon'. We all know they are bored and stuck in a rut with a low paid dead-end government job where people who flip burgers at McDonalds make more money and they are always looking for ways to acquire free new shiny toys to use in their man-caves with MAME. You can't fool us damn government a-holes!

Uh hum, getting back on track, so inside the black gun it's identical of course. I first tried the easiest and less intrusive thing by swapping the cable by desoldering it from the PCB at the connector and soldering it onto the non-working board. That didn't make any difference. The next thing I wanted to do was prove the BA7071 sync chip was good so I removed it from the non-working board and put it on the working board. The black gun worked fine so the replacement sync chips are ok.... good to know!
I also swapped out the 10uF 16V SMD electrolytic cap but that also didn't change anything.
So at this stage I've swapped the cable, light sensor, SMD electrolytic cap and the crystal is working. I've measured the SMD resistors/caps and there's nothing remaining.... hmmm.... except the custom chip. Urgghh! Ok well I decided I must know either way so I desoldered and swapped over the custom chip and that has to fix it!
Namco Guncon-45 repair Namco Guncon-45 repair Namco Guncon-45 repair
I tested it and the gun still doesn't work! I took the original custom chip I removed from the non-working board and put that onto the working board and the black Guncon still works so the custom chip is ok.
Hmmm, now it's time to get serious. If you thought I was serious before you ain't seen nothin' yet!
I found a schematic on the net but it's incomplete so I reversed the board and made a rough and dirty schematic.....
Namco Guncon-45 repair

You're probably thinking 'wow that looks rough and dirty!' Well yes it is, I already said it's rough and dirty, pay attention people! ;-)
Regardless of how bad it looks it's 100% complete and if you view it full size it's plenty readable ^_^
When making the schematic I removed all the caps on the working board and checked them out of circuit. The caps connected to the crystal measured a strange value, but swapping in some more standard 22pF caps caused the gun to not work at all. On the non-working board I used my multi-meter and the schematic as a reference to beep out all the connections and they were all ok.
Maybe I should check to see if the thing is active. I had no easy way to hook up my logic probe so I soldered some wires onto ground and 3.3V and hooked up my logic probe.
Namco Guncon-45 repair Namco Guncon-45 repair

According to the incomplete schematic I found on the net, pin 9 of the custom chip should have a 1kHz signal on it. I assume that's only there as a test point just to check that the custom chip is working. I probed the test point and it was active. I used my frequency counter to measure it and it showed 1kHz so the custom chip is working. Well I know that anyway because this custom chip is the one that came from the working gun ;-)
So now what? Well there's no point probing the non-working board further because I have nothing to compare it to. So I hooked up some wires to the working board and went over the entire board and checked all the connections at each part and stored that in my brain. With the Guncon plugged in and Point Blank running on the Playstation I probed the sensor output and noted that the probe changed from static high to active when the sensor was pointed at the TV and when I covered the sensor with my finger the signal went back to high again. This shows that the sensor is working. Then I transferred my logic probe to the non-working board and probed all the same points. It all appeared the same except the composite video signal on pin 9 of the cable connector. On the working board the signal was a normal composite video signal. On a logic probe that means it's a low active signal but through the logic probe piezo speaker it sounds dirty and growly like an angry dog. On the non-working board the video signal was just low, but not completely dead, with very minor activity. It sounded more like a slightly annoyed guinea pig hehe! ;-)
Let's have a look at the BA7071 datasheet....
Namco Guncon-45 repair

The datasheet shows the input is on pin 1 and output is on pin 8. There are some other outputs too but on this board they are not connected. I probed the sync output from the BA7071 and it kind of looked about the same as the working board but I suppose it's very subtle after the video is stripped out of the composite signal. The input pin 1 also probed as a low almost non-active signal. Something was pulling the signal down. Well there's only a few parts between the connector pin 9 and the BA7071 input pin.....
Namco Guncon-45 repair

I removed the 220 ohm resistor at R6 which is directly connected to the cable connector pin 9. This effectively isolates the PCB from the video input so that the PCB has no effect on the signal. I probed the cable connector pin 9 and the composite video signal was present and active. The angry dog was back! I checked the resistor I removed and it measured 220 ohms so it was ok. So the problem had to be with the 3 SMD caps. Those caps are in parallel and when you measure caps in parallel they just get added together. On the working board it measured around 1uF across the caps. I measured the caps across the same point on the non-working board and got around 375nF. Hmmm, that ain't right! Since the caps are in parallel it's impossible to measure them individually so I removed all 3 using hot air. Hmmm, but I did that before and they tested ok??? I tested the caps individually using my component tester and one of them would measure good the first time, but when I checked it immediately again it would not give a reading and the tester would just sit there trying to test it but never show the measured value. Ah! That explains why I got a good reading the first time.... it gives a good reading when checking it fully discharged but not when checking it again after it is charged. When I checked the caps originally I was tricked! Out of circuit the good caps measured about 360nF. This doesn't seem to be a nominal value. The closest I found was 330nF. The next nearest is 470nF. I didn't have either in stock in 0804 SMD caps. Since the caps are in parallel the actual cap value connected to the input is really just 1uF. I did have a 1uF SMD cap in stock so I just left all the old caps off and fitted a single 1uF SMD cap. I replaced the 220 ohm SMD resistor, powered on the Playstation/gun and checked the sync input on pin 9 of the cable connector with my logic probe and the video signal was active. Looks like it's fixed! I loaded Point Blank on the Playstation and at the gun calibration screen I aimed and pulled the trigger....
Namco Guncon-45 repair Namco Guncon-45 repair

YUP! The cross-hair appeared and moving the gun also moved the cross-hair. The game asks if the gun is aligned correctly, which of course it is now that it's working :-D
So the fault was just a bad SMD cap that was pulling down the composite video input. Funny how it's always the last part you check/change, but in this case it really was the very last part on the board. If it wasn't that cap there was no where to go next hehe!

Finally, to finish it all off I removed all the silly orange stickers and cleaned all the scum off it so it looks new. Now I'm ready to rob a bank with it because without the orange stickers it's totally believable that it's a real gun.... at least it would be if you believed all the political bullshit ;-)
Namco Guncon-45 repair

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