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Pre-show testing found that there was a slight graphics corruption on some of the sprites
used in the later levels, for example the vaulter sprite was bad. I suspected a bad sprite
graphics ROM and removed each one:
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There was no boot of either main or sound and reset wasn't active. A manual reset didn't
change anything and the scope showed the address bus as a counter with active data bus.
Replacing the Konami-1 CPU didn't change anything, and the Arduino ICT was setup. "ROM
Check All" failed with an intermittent CRC on ROM G5. Checking each ROM found them all to be
intermittent and I suspected a bus fault. Removing ROMS 2 to 5, leaving just ROM 1 G5
allowed the ROM check to pass. The remaining ROMS were added back one-by-one:
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Sound was a continuous unchanging buzz starting a couple of seconds after power on. Checking IC B18 (Z80 CPU) with a scope found RD, M1 and data bus all active. On coin, pin 16 INT was asserted low and stayed low suggesting no response from the CPU. IC B18 was removed and replaced with a socket to allow the Arduino ICT to be inserted. The ROM check passed but the RAM check failed "E:C16 4000 01 00". Its nibble sibling C17 passed OK so I suspected IC C16 (2114) was bad. Replacing IC C16 (2114) fixed the ICT test and with a Z80 CPU the sound was back working OK.