When I first got it it had extremely quiet sound that could only be heard at max volume on the tv with no sign of audio on the headphone jack at all. I took it apart expecting a sea of bad caps only to find that the previous owner had already mostly recapped the system. However, they didn't replace the 4.7 and 100uf caps by the headphone jack/AV out jack or the 22 and 100uf ones nearest the cd drive. Also, being new to duo repairs, I'm not sure if this is a normal thing, but there was a jumper wire running from pin 82 of the D91317GD to pin 14 of the Oki M5205.
I measured the voltage across IC506 and it was only 3.6 volts from power to ground. So I tried cleaning the remaining cap residue and flux from the last owners repair job and flushing underneath the opamps with 99% isopropanol to clean them out. When I put the system back together there was no longer any sound at all and the voltage at IC506 was down to only 1.6V. I tried removing, cleaning and reseating said chip, but there was no change. I've uploaded some pictures of the board including some highlights of areas I think are suspicious if anyone can spot any obviously fried components I'm missing. As well, it looks like there are some corroded vias. What's the go to method of repairing those?
https://imgur.com/a/c7tbzPhThe last thing I checked was the power on IC502. I've seen elsewhere that it's supposed to read 5 volts, but I only got 3.8. Could that be my culprit?
Measuring more values, Q304 reads 12V on C, 9V on B and 1.7v on E. According to this post that sounds wrong. is it more likely the transistor is damaged or is something upstream from there failing?
https://www.pcenginefans.com/forum/index.php?topic=23041.msg515978#msg515978
Topic: Tired ground I'm sure, but I just got myself a PC engine duo with sound issues (Read 303 times)