Apr 192019
 

I got a Megablast board that was not booting at all.

1) As reported on Caius Liquid Kids repair log (http://www.jammarcade.net/liquid-kids-double-repair-log/), it is common on these Taito F2 system boards that TC0220IOC custom chip is faulty in this case (I suspect plugging the board to the JAMMA connector upside down may fire that chip, sending it +12V via the I/O ports. That’s probably what happened here).

Indeed, after swapping the TC0220IOC chip from a donor board, the game booted and offered me a nice glitched screen:

2) Another common issue on these Taito F2 boards are the mask roms getting internal disconnections within time. So I started replacing the background ROM (C11-05 @ IC58) by an equivalent 27c400 programmed EPROM and got backgrounds fixed:

3) Anyway, all the sprites were missing. After a long search and many tries I found a weak signal on one of the RAMs data line that carry sprites information between the main CPU and the sprites generator custom chip TC0200. Replacing the RAM (a TMM2063AP @ IC50) made sprites appearing, but glitched:

4) I found out that one of the sprites ROM was dead as well (C11-04 @ IC31). Replacing it with a programmed 27C400 EPROM fully restored the graphics:

5) & 6) One last thing I didn’t mentioned yet was the sound that was scratchy. More precisely, sample sounds were clearly corrupted, not the FM sounds. With no surprise, I found out that both IC where audio samples are stored (C11-01 @ IC29 and C11-02 @ IC30) were dead. Replacing them with equivalent 27c040 programmed EPROMs totally restored the sound.

Board is now fully fixed. Here is an overview of the chips I had to replace on my board (interesting fact is that Caius had to replace the exact 4 same mask ROMs on another Megablast board: http://www.jammarcade.net/megablast-repair-log/):