Professional software development, amateur BMW tinkering, old arcade game stuff


Technos Wrestlefest arcade pcb repair

Two different boards with the same sorts of glitches – corrupt sprites, bad palettes and sometimes no video output at all.  Sometimes the corruption would change if you pressed on different chips on the board.

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Pressing on the board to make a difference is often a hint surface mount custom chips are not making good contact.  On both boards some pins of the TJ-003 custom were lifted and not making a solid connection.  On one board the TJ-002 custom also had some lifted pins.  The solder was reflowed and both boards back to 100%.






Taito Twin Cobra arcade pcb repair

A slightly unusual fault as this board stalled on the check screen, but reported everything ok.  If RAM, ROM and sound are ok then why doesn’t it work?  Without much to go on I fired up MAME to see what the CPU is actually doing at that point in the debugger.  The answer is the 68000 starts communication with the TMS32010 protection microcontroller.  Disabling the microcontroller in MAME made the emulation act like the physical board as the main CPU waits forever on the protection response.

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On the real board the TMS32010 is hidden under the T.TC-4 sticker.  A logic probe showed it was getting a clock signal but most data and address pins were weak or dead.  The game booted perfectly using the T.TC-4 from another parts board, so that confirmed the microcontroller itself was dead.  Replacement is the only option as I don’t think blank versions of this part are available anymore.

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Konami Jail Break arcade pcb repair

Essentially the same fault and repair as my earlier Green Beret fix which is almost the same board.  Corruption in sprites and the corruption was in ‘screen space’ as opposed to moving with the objects.

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The 4 RAM chips in the top right of the board next to the square custom are used as line buffers for the sprites.  Replacing these fixed the sprites.



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Taito Chase HQ arcade pcb repair

Initially a completely dead board, with no clock signal at the CPU.  Some probing revealed the crystal oscillator didn’t have any power going to it, and in fact nothing on the top board had +5V.  There was a very unusual broken trace on the main +5V line from the edge connector, and a handful of capacitors that had pretty much came apart.

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With that fixed the board booted to a lot of garbage graphics – no sprites and no road layer.


The road layer is handled by the top board – pretty much the custom chip, two RAM chips, a ROM and a PROM (the other two RAM chips in that corner are the palette RAM).  In this case the 63s141N PROM had failed and had dead outputs.  A PROM was taken from another board and the road layer fixed.


The title screen had some interesting sprite behaviour – the first entry in the sprite list seemed to be drawing somewhat correctly (The ‘CH’ of the Chase HQ logo).  That made me wonder if some kind of counter had failed and it was only processing the very first address of sprite RAM over and over.  There are a bunch of LS161 counter chips on the video board and there was a dead input on some of them.  This traced back to a PAL chip which was replaced by one from another board and all sprites displayed, albeit with a lot of garbage and vertical line corruption.

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The final part of the puzzle are the 16 sprite work RAM chips on the video board – if any of these fail it will tend to be vertical lines or other corruption throughout the screen.  The sprite RAM seems to be in ‘screen space’ – so faults don’t follow the sprites but instead have constant positions on the screen.  On this board 5 chips were confirmed as bad and when replaced the board was 100% again!

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Konami Iron Horse arcade pcb repair

Terrible corrosion on this pcb, in fact all of the ROMs disintegrated on removal so new ROMs were burned and some sockets replaced.  With that done the pcb still only booted to garbage on screen and constant watchdog resets.  Watchdog resets usually mean the CPU program isn’t running.  On this board the watchdog can be disabled by bridging the jumper J1 near the edge connector, and this showed the CPU was trying to run with data & address bus lines active but there had to be some other fault.

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The schematics show the CPU part of the board is pretty simple, so I removed and tested a few chips (Fujitsu LS139 and LS245) but they were ok.  Further logic probe tested revealed the LS245 ‘dir’ pin seemed stuck – this comes from R/W pin on the CPU so it seemed the CPU was never writing any data.  Even if the CPU was just executing random garbage some writes would be expected.  So the CPU (6809E) was desoldered and a socket and replacement installed.  The LS245 dir was now pulsing as expected, so it seemed the old CPU has indeed failed internally on that line.  Still garbage on screen, but now the garbage consistently changed after a second as if the CPU – maybe it was trying to show the ‘BAD RAM’ screen but if all the RAM truly was bad then that screen itself would be corrupted.

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Desoldered the main 6264 RAM – which passed in a tester, and also socketed and swapped out the two smaller 4464 RAM chips.  This had a positive effect on the garbage as now proper sprites could be seen instead of just lines.

All the other TTL related to the CPU and graphics chip seemed to check out so I was stuck for quite a while tracing out all the address & data lines from the CPU to the graphics chip.  At some point I removed and re-seated the RAM, ROM and custom chip and the thing burst into life.  Some of the address lines must not have been making good contact through the socket.

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Capcom 1943 arcade pcb repair

A clean original 1943 board, which I can tell is the original Japanese version by the ‘BM’ (Battle of Midway) stickers on the ROMs. The board booted to a black screen with a single pixel vertical line of colours.


Logic probe showed nothing ‘looked’ wrong – CPU running, data and address lines pulsing, output on the program ROM pulsing, etc. When I shorted some data lines together though some sounds would randomly play and a stuck screen of graphics would show up. This at least told me the sound & graphics were working, I assume the CPU was executing garbage and when I shorted lines together it just happened to force it to write different data to the audio CPU and graphics board.

I dumped the main program ROMs and 2 out of the 3 matched the 1943ja set in MAME. I burned a replacement for the mismatch and tried it on the board but it made no difference. Without much else to go on I removed the main RAM (TMM2063) and installed a socket and replacement RAM – everything worked 100%! I replaced the original program ROM and it kept on working, so the RAM was the only fault.


Let’s return to why the BM01 program ROM didn’t match the MAME set by disassembling them and comparing. Rather than find this is just random bit rot, there are 3 deliberate changes to the Z80 program code.

MAME set (1943ja)

0A7C: 3A 07 C0 ld a,($C007)
0A7F: B8 cp b
0A80: 18 17 jr $0A99

New set

0A7C: 3A 07 C0 ld a,($C007)
0A7F: B8 cp b
0A80: 28 17 jr z,$0A99

So in the new set, the program loads a byte from $c007, compares it to register b, then if equal jumps to location $0a99. In the MAME set, it loads the byte, compares it – then jumps regardless of the comparison. Why bother reading a byte and compare if you don’t care about the result? Well, this makes sense when you realise $c007 is the security protection device. The 1943ja program has clearly been patched to ignore whether the protection checks pass or fail. The new set is surely the pristine ‘original’. 1943ja has two other patches at $b02 and $281e that work the same way.



Capcom Buster Bros / Pang arcade pcb repair #2

A dirty beat up board showing no signs of life (not only no video sync but no activity on any TTL anywhere on the board). Previous owner had installed a ‘desuicide’ patch (see other Pang repair) but there was obviously another problem if the CPU is not getting a clock signal.


The crystal oscillator on the board was rusty and had obviously taken some physical damage but it still worked so the next step is to trace where the output signal goes. And it went pretty much nowhere – terminating at the empty FB42 pad right next to it. Closer comparison to a working board showed there should have been a component there, it must have been physically broken off the board (however FB43 is intentionally empty). I wasn’t familiar with this type of component package but apparently FB is ferrite bead in this context, which is usually used as a high frequency filter. The Capcom packaging isn’t one I recognise though and it has no markings on it to indicate the frequency or impedance.

So without a replacement I just bridged it with a wire… you shouldn’t really ‘need’ a filter right after the oscillator even if this board’s designers intended it that way. So with that patched the board sprung to life with a solid green screen – so clearly the clock signal is now reaching the parts of the board it’s meant to.

Solid green screen is an indication the CPU isn’t running, perhaps because of the battery suicide. I took the CPU and de-suicide ROMs from the other working board and tried them here – board came up straight away, 100% working graphics and sound!


So by trying combinations of ROMs and CPUs from the two boards it became clear the encrypted Kabuki CPU itself had failed. That’s unfortunate but not a big deal as with the de-suicide ROMs and patch a regular Z80 can be used in it’s place.

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SNK NeoGeo 4 slot arcade pcb repair #3

This was an interesting one..  It’s the newer style 4 slot with the custom chips on the top board replacing lots of 74LS TTL chips.  A previous owner had installed the Universe Bios onto it, but games would crash right after the NeoGeo startup logo screen or the ‘Winners Don’t use Drugs’ screen (if the BIOS set to US region).  Puzzle Bobble showed corruption then a crash and Super Sidekicks 2 would jump to an ‘illegal instruction exception’ screen.  (Reinstalling the regular BIOS just led to a crash and watchdog reset at the same point).  So this is quite interesting because for the startup screen to show up the CPU must be executing the program on the cartridge.  So the data bus and all control signals must be working between the bottom board and the top board.


My best guess was that an address line was faulty – this would let the CPU execute code as long as it didn’t jump to any areas of ‘bad’ address.  A cool feature of the UniBios is that has a memory viewer – so I was able to look through the memory the 68000 on the main board can ‘see’ of the cartridge.  And at 0×10000 the data was identical to that at 0×00000.  So that means that address line A16 must be stuck low – whenever the CPU asks for data in the range 0×10000 to 0x1fffff the cartridge is actually returning 0 to 0xffff.  So explanation for the illegal instruction found!  The CPU would jump to somewhere in that range – but actually be given illegal instruction data from elsewhere in the ROM which causes the exception.


So, time to trace out where A16 goes from the main 68000 CPU on the bottom board, and also trace where cartridge A16 goes on the top board.  (Technically it’s A15 on the cartridge side because it’s a 16 bit ROM rather than 8 bit, but I’ll call it A16 to be clearer).  Interestingly I found some marker pen marks at some of the A16 points on the lower board, so someone had clearly worked on this before and also suspected an address fault.  The main paths for the address lines are to go to the BIOS rom on the main board and to the 245 latches in the lower right of the board.  Now I was looking closer I could also see one of the original AS245 latches had been replaced with a LS245 version and A16 went through this chip.  So someone had definitely spent some time on this before.  The address lines then go from the 245′s to the top board connector.  On the top board I was hoping to find a broken trace to explain the fault, but continuity tested all the way from the bottom board to the NEO-244 custom chip (A16 goes to pin 1).  Tracing from the cartridge connector back showed no breaks either – all address lines are shared between slots 1 & 2 on the board, and A16 traces back to the same NEO-244 chip – pin 62 this time.

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So a logic probe showed that the input would pulse whenever the 68000 asked for A16, but the output to the cartridge slot was always stuck low.  So the conclusion has to be that this custom chip has failed.  Unfortunately it’s a relatively rare custom chip as I believe it’s only used on this revision of the 4 slot and the accompanying 2 slot (MV2F).  I wasn’t really sure why this chip was needed at all though…  Yes, there are 4 slots but the 68000 is only going to be accessing one address at a time – so why can’t the cartridges just be addressed straight from the 68000/AS245?  So.. I lifted pin 62 of the NEO-244 and patched the pin 1 input directly onto the pin 62 output pad.  Games in slots 1 & 2 now work 100%!

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Slots 3 & 4 still gave the illegal instruction exception – all address lines are common between these slots, and A16 traced back to the same NEO-244 custom, pin 63.  So it’s now clear what NEO-244 does – it takes the address bus from the 68000 as input and drives either slots 1 & 2 or slots 3 & 4 depending on which is active.  So again I lift pin 63 and patch pin 1 onto the pin 63 pad and now all slots work!  I’m not really sure why an address bus selector is needed – there’s no reason from a logical design point of view as program address lines in all slots can be driven simultaneously.  The only reason I can think of is implementation side, maybe trying to manage the current associated with driving 4 things from the single AS245 output.




Data East Bad Dudes arcade pcb repair #2

This pcb booted to obviously corrupt colors on the title and hi-score screen, but then in-game all the sprite colors and most of the level colors were correct.  At first I assumed this would just be corrupt graphics ROMs but they all read with the correct CRCs.  I switched a Hippodrome game board onto the Bad Dudes main board as they are compatible and the Hippodrome title screen was now corrupt, so this narrowed the fault down to the main board rather than the game board.

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Because the sprite colors were good it’s unlikely the palette RAM was at fault as all layers share that RAM.  The custom graphics IC’s output directly into the palette circuit on the board, so hoping the custom IC’s weren’t bad I piggybacked spare chips into the palette section as shown in the schematics.  (If a chip on board has dead outputs the ‘piggyback’ gets the same inputs and can drive the outputs again).  Success!  I removed each piggybacked chip one by one until only one was left – LS157 at 17H.  Old chip was removed and replacement soldered in and board 100% again.

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SNK NeoGeo 1 slot arcade pcb repair

This 1 slot booted up with ‘Z80 error’.  A previous owner had obviously tried to fix this and had removed the old Z80 and installed a socket and new one.  With the Z80 removed though it was clear a tiny trace had been lifted off the board when the work was done.  I removed and replaced the socket and repaired the trace but still got ‘Z80 error’.

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Making sure all address and data lines from the Z80 reached the ROM was the next step, and indeed another broken trace relating to the original socket was found.  Still ‘Z80 error’ after this was fixed.  All address & data lines to the RAM were then checked with no problems found.  Without much to go on I desoldered both the ROM in case the program was corrupt, and the RAM in case it had failed.  Both tested fine off-board.


Next up is to try and check if the Z80 can communicate with the 68000, as if it can’t the 68000 will always print “Z80 Error”.  On all but the early 1 slots a custom chip handles this – NEO-C1.  The top left corner of this chip takes the 8 data lines from the Z80 to pass info to the 68000.  I checked continuity from these 8 pins back to the Z80 data pins and only 4 were connected…  It seems 4 of the lines had corroded near the battery although they visually looked reasonable.  4 patch wires were soldered underneath the board and everything works!  Most likely this was the original fault all along, and the Z80 itself was fine to begin with.

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