Sega ST-V Audio Repair

I was sent a Sega STV board to do some custom wiring on. After some testing I was getting mixed results with the audio output. The board sounded good from the JAMMA edge, but when connecting to CN24 for line level audio via the STV IO Board the right channel was dead. The JAMMA edge most likely sounded ok because the left audio is duplicated to right channel on the in the cabinet for dual mono.

I had good continuity from CN24 headers back to TDA1386T chip. This chip is the digital-to-analog converter that takes digital signal from the main sound chip (YMF292-F SCSP) and outputs left and right analog channels. 

A logic probe on TDA1386T (datasheet available here) shows pin 18 (left channel) hi with intermittent audio activity, but 21 (right channel) hi without audio activity. I’m still learning to use the logic probe and it’s probably not the best tool to troubleshoot an audio issue like this, but it worked. The input signals seemed to probe ok so I suspected the TDA1386 to be faulty.

I harvested a TDA1386T from a busted Sega Saturn, used a hot air station with some kapton tape to protect nearby components, and replaced the chip on the STV. The right channel came back as suspected.