Problem

Distorted music and very quiet sampled sounds (e.g. applause and bonus item appearing):

Diagnosis

Namco System 1 has three sound sources: a YM2151, a 63701 MCU acting as a sample player and a wavetable sound generator. The DACs for each of the three stages are shown below:

Both the FM and samples sections each use a TL084 op-amp.I’ve repaired three System 1 boardsets recently, each with similar audio faults. In each case, one or both TL084’s were defective. I don’t have oscilloscope traces that conclusively prove that either TL084 are defective here (I find analog audio quite tricky to debug) but I was willing to bet that, for a fourth time, shotgunning both would fix the issues. Indeed it did…

Fix

Replace TL084 at P5 (fixed distorted FM).

Replace TL084 at P4 (fixed quiet samples).

Philip Bennett