Status: FIXED
Repair cost: $2 (questionable if part was really needed)
KLOV Post: http://forums.arcade-museum.com/showthread.php?t=146427
Symptom: Game board exhibiting strange display behavior – random vectors scrolling back and forth across screen. Game plays blind.
Diagnosis: Problem located on AVG board.
Fix:
- 08/21/2010 – AUX board and cable verified good. Tested individual boards on a working setup. Problem is located on AVG board.
- 08/22/2010 – Cleaned and reseated 5 socketed RAMs, the 2 vector ROMs, and the CPU. Board now has no XY output voltage.
- 08/24/2010 – Tested several chips in the vector generator data shifter section, which confirmed good. Logic probe pointed to DAC-312 @ D10. Replaced with no change.
- 10/30/2010 – Began with game in test mode, no display. Swapped CPU with known working 6502 and got a single blue vector on screen and activity on the slam switch (switches test screens) and long steady beep. Confirmed activity on CPU pin 37 & 39. Activity on E2 pin 1 & 2. Confirmed ROM activity on the CS1 & CS2 lines. Theory of operation doc said long steady beep in test mode points to bad vector ROMs. Flip-flopped the ROMs (socketed) and test pattern appeared. Adjusting X/Y position, linearity and BIP controls brought test pattern into view. Went out of test mode and game worked.
Notes: DAC replacement could have had an effect, but hard to tell since game was dead – DAC outputs never changed, but inputs upstream were still bad at that point. However, after the DAC replacement, I never saw the pattern shown in the video again. Original CPU was later confirmed good. Bad/dirty sockets ended up being the culprit despite cleaning of chip legs and using contact cleaner before they were inserted into their respective sockets.
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