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Konami Track And Field arcade pcb repair #3

Board booted to a screen full of zeroes which is an indication the CPU is running the start of the program at least (if not the screen would be full of random garbage rather than a consistent pattern).  Checking the eproms on PC found a couple were bad (inconsistent reads) but the main problem was the RAM chip next to the eproms was dead.  The part number is scratched out but it’s just a regular 6116 style RAM.

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With that replaced the board booted to the title screen – but with obviously bad sprites in both the tile index and the Y position on screen.  The game also reset before entering gameplay, so definitely still a CPU/RAM related problem.  There are schematics available for this game, which show the custom chips used for sprite processing.  This board however, didn’t use any custom chips but instead had little daughterboards with regular TTL chips.  This is actually quite common in all of the Centuri licensed boards I’ve seen – probably there was a manufacturing shortage of the custom chips and the daughterboards were put in to meet demand.  I set about removing the daughterboards for test (the board should run without crashing, just no sprites, with them removed) and the board ran fine.  I then ran the board with the daughterboard sitting in the desoldered holes – and it ran 100% fine with working sprites!  It kept on working with the board soldered back on and a long soak test.  Very strange, I can only guess there was some kind of solder bridge short on the board somewhere, and the act of applying heat to remove the daughterboard cleaned it up.

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Finally bad inputs were fixed by replacing a smashed resistor pack with one from a parts board.

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