Konami X-Men arcade pcb repair
This pcb was a mess of previous repairs and missing parts – two crystal oscillators missing, program ROMs missing, audio mask ROM missing, various TTL and RAM chips replaced. So clearly many problems in the past and someone likely tried to repair it, failed and then harvested parts to fix other boards.
I pulled some crystals from a parts board (Konami Run and Gun) and burned some fresh program ROMs from the MAME set. Game booted to a solid yellow screen. Like the Vendetta repair I suspected palette RAM and when new RAM was piggybacked on top the usual Konami check screen came up with a bunch of errors.
Eeprom @ 13B error
13B is the eeprom used for storing game configuration data – when I tested this with a logic probe there was no data output – but actually there was no +5V to it either… it seems this was a victim of a previous repair attempt – it had been removed and replaced, but had a bad solder joint on the +5V line. With that corrected the game still reported an error – and this time the data pins were active. Schematics are available for this part of the board and there was no continuity between the two outputs of the eeprom and where they should go – trace damage from the previous repair attempt. Patch wires soldered on the bottom of the board – and success! The screen was no now longer upside either as the game stored the flip screen configuration data correctly.
The remaining errors all related to the audio section of the board. Like Vendetta I decided to patch the program to skip errors and see what happened.
Broken Colour Output Custom
Well, the game ran surprisingly well! All graphics and inputs were working, just no sound, and clearly no blue colour in any graphics. There are schematics for the video output, which consists of two LS273 latches and a bunch of LS07′s. Logic probe seemed to show this was all working correctly, so the problem was likely the custom 052535 IC – a replacement was taken from a Run n Gun and the blue channel restored.
Errors 6F, 7G, 4E, 2D are all in the audio section of the board – program ROM, two RAM chips and the missing mask ROM. Piggybacking RAM had no effect, and the program ROM was freshly burned from MAME so it should have been correct. Further probing revealed the Z80 CPU was not even running – no activity on data or address lines – so it makes sense the main CPU reported all the audio parts bad.
Before declaring the Z80 dead I checked the control lines – and the WAIT line was being held – so something was actually forcing the Z80 not to run. No schematics are available for this section so I traced the WAIT line to the output of a LS08 chip – that’s just an AND gate – and eventually traced the input to the gate from the custom audio chip. So some info not in MAME is that the audio chip actively controls the Z80 wait, probably when accessing shared memory.
I temporarily removed the LS08 so the Z80 could run and there was activity on the data and address lines so the CPU itself was probably good. At this point I stalled for quite a while with no ideas. After finding the bad Konami PAL on the Vendetta repair though I checked the X-Men audio PAL and it was completely failed. When replaced some synth sounds could be heard during the game! The WAIT problem turned out to be the custom chip was not getting a clock signal – the Run N Gun dual frequency crystal was bad – so one was taken from a working game (Premiere Soccer) and the LS08 replaced – this finally cleared up all the audio errors in the self check.
Final problem was the missing sample ROM – a 2 megabyte 27c160 eprom can be used here as replacement. Lots of traces on the board had been damaged but all address/data lines are shared with the custom audio chip so a logic probe in the socket will show if any lines are disconnected.
Unusual to see a board with so many unrelated problems, but fixed 100% at last.