Pang! 3 Arcade repair - garbled graphics

The arcade board is said to have garbled graphics.

Board looks okay, a few scratches but tested continuity fine. Some pins on the bottom board seem dangerously too close, needs to be bent.

The sub daughter board has some serious factory bodge.

The JAMMA connector has been reworked on, RGB changes when tilting the connector. This will be addressed after the main issue is fixed.

The game powers on but all sprites looks square and incorrect. Seems to pass POST and runs. No sound but hissing from amp can be heard.

Diagnosis

Find no address bus activity on the sound ROMs(oki ROMs)

Dumped ROMs, verdict: 11D.bin: good, oki ROM 11L.bin good, maincpu ROM 10D.bin: good, oki ROM 10L.bin: good: maincpu ROM

So all the socketed ROMs appear to be good.

Cleaned ROMs / PROMs and sockets, still boot to the same garbled image.

Not ROM, not contact issue. The board has been swapped with a know-good CPS-1 A board, which boots to the same picture. The issue is on B board or C board.

The repair

Scoped, the SOIC packaged LS245 buffer IC on 1C has irregular output. Reflowed, the image appears to be correct, in gameplay.

But not all the tiles. In character selection some characters looked wrong. In panic mode BG, all black in level 1. Normal mode, level 1 BG has incorrect tiles. Are these pre-existing issues? The customer said no.

So more buffer and other 74 chips to be reflowed. Reflowed all the SOIC packaged 74 chips. Turns out the BG tile is appearing but with repetitive pixels. The 74LS08 AND gate chip (location 1J)has only one channel used, but the output seems to have lower voltage and slow output.

However, by the time I’m checking it again, the issue is gone. The picture including BG tiles are all normal now. Well, sometimes you get this erratic logic chips. Could be the solder residual though.

Unless this 74LS08 is showing issues again, this Pang! 3 is fixed.