PCB Repair: Wyvern Wings

Problem

Background layer corruption.

No sound or music, except for occasional short bursts of noise.

Diagnosis

Gently flexing the PCB around the area which contains the graphics flash ROMs caused the background issue to disappear. On closer inspection, the solder joints on the legs of the flash ROMs appeared rather iffy:

After generously applying flux to the legs, I carefully went over them with a soldering iron fitted with a conical tip intended for drag soldering:

As all of the flash ROM legs looked rather dicey, I decided to reflow them all. After leaving the PCB to cool down, I re-tested it and found that the graphical issues were now fixed. Great!

Next came the sound issue. Given the occasional bursts of noise, I was fairly certain that the analog/amplification section was at least partly-working. The fault was most likely to lie within the digital section.

The sound hardware is based around an AdMOS QS1000 MIDI synthesizer, which incorporates an 8051 MCU and wavetable engine in the same package. There is a generic instrument ROM (QS1001A), while game-specific sound effects are stored in an additional flash ROM. The QS1000 can be driven via a serial interface but instead the Semicom games use an external ROM which contains the 8051 program code and MIDI data:

The QS1000 has a serial output to a TDA1311 stereo DAC. The BCK and WS inputs were being driven as expected but the DATA input was almost permanently low. I verified the program ROM (U7) against the MAME ROM set, checked the 74LS373/374 latches and confirmed that the QS1000 clock input was good. Checking the pins of the SFX ROM (U15A), it appeared one or two pins were poorly connected. I reflowed U15A and U17 and whoomp, the sound and music returned.