PC Engine Duo Sound issues

Hello,

I recapped a PC Engine Duo a few weeks ago, and immediately ran into crackling sound issues. It's mostly sat on the shelf because I've been busy with the end of my college semester.

I have since re-cleaned the board, and now instead of the crackling sound issues, I get what seems like no sound. However, if I crank my PVM to max volume I can faintly hear the sound, and it sounds like it should. If I'm not mistaken this is a sign that the amplification circuitry is malfunctioning.

My guess is that I have a dead trace or via somewhere, and I'm having a bit of trouble tracking it down.

Does anyone have any suggestions for this? I know the op amp circuit near the AV jack has some issues, as the voltages seemed off when I probed around. (1.4V on the output, 3.8ish on the non-inverting, and I think 4 on the inverting? Been a bit since I measured it.)

Has anyone reverse engineered the audio circuitry in the PCE/Turbo Duo? Some sort of a schematic would be extremely helpful here.

Thanks in advance for any help. It's appreciated.

 

I managed to figure it out, and repaired both the hucard and CD audio for the console.

The problems were a missing ground connection on an op-amp, and a missing 5V rail to pin8 of the M51131L volume control IC. 2 jumper wires and the audio was working perfectly again.

After that I went to reset the laser, and found that it was a bit... touchy. It likes to randomly go out of calibration, so I decided to just replace the entire HOP-M3 laser assembly and tune the new laser.

May also need to replace some of the trimmer pots for it if that doesn't fix the issues.

 

Good work dude.

I have the same issue actually. Unfortunately my tester is broken so I can't test the legs on the amps and the IC sound chip.
Did you manage to find a schematic for the sound? I'm having a look around the internet..

Or did you just poke around with a continuity tester and look at what the pins were supposed to be doing/outputting and work from there?

Thanks in advance.

 

Check all of the op amps. Pin 4 is ground, Pin 8 should be about 7-8 volts. I mostly fixed it using a voltmeter and a continuity tester/ohmmeter. An oscilloscope may also prove useful.

There are some partial schematics floating around PCEngineFx forums, but no full schematics that I know of. Makes troubleshooting the console a pain.

Basically just start checking stuff. If you have a microscope you can use that to look at the vias to see which ones look really nasty. Other than that just check all the op amps, caps, etc. in the upper left portion of the board near the AV jacks. Don't forget the ones on the back either.