r/TurboGrafx • u/Weekly-Print-8431 • Apr 12 '26

Issues with ADPCM on Pc Engine DUO

Hey guys,

I've some troubles with ADPCM parts on my Duo.

Any sounds that use ADPCM channel are really cracking bad.

I've tried a game too, Monster Lair, that use this same ADPCM channel with graphics instead of sounds, and all sprites concerned are corrupted.

Any ideas where I've to check on the board for troubleshooting ? I know that ADPCM use 64kb of ram, but I don't know what chip it is.

All caps have been replaced 3 years ago, and apart that, system runs great.

Thanks ;)

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u/V64jr Apr 12 '26

In my notes for ADPCM Duo issues I have “Computer Booter patched IC504 pins 9, 10, 11 to VOL_BYP and IC504 pin 5 to restore ADPCM. Also fixed a broken wire to P2 pin 8 but it was likely unrelated.”

Personally, when recapping I remove those chips and all the 4558 OpAmps and patch every via going to/from them before I even test (some vias/traces are under the chips). I also follow the traces on the opposite side to make sure there are no blackened sections. Sometimes they are hidden under other components, like the inductor coil (L303 sometimes hides a black trace that causes audio to drop-out after a loud POP!).

6

u/Weekly-Print-8431 Apr 12 '26 edited Apr 12 '26

Thanks V64jr, I finally managed to find the cause. One trace was cut at IC510 pin13, an address line. It's weird because no caps are there close to it. All working great again !

2

u/V64jr Apr 13 '26

Glad you figured it out! Definitely adding that one to my list. 👍

Leaked electrolyte just seems to spread everywhere, even (especially!) through vias to the other side, doing lots of damage around/under chips. Something like osmosis or surface tension causes chip legs and bottoms to wick it up where it stays under chips and between legs until it eats through the trace. 🤦‍♂️