Post by edison517 on Jun 7, 2022 11:12:35 GMT -5
Just wanted to let people know about an issue I fixed with a UMC-200.
Unit would power up/on, but no audio would come out.
I did the 5v cap updates; no change.
Did more troubleshooting and discovered the +12v rail was at P2, but the -12v rail was not. The transformer was supplying the negative 16vdc, but that voltage wasn't getting to the negative 12v regulator (IC3).
I used an external power supply to directly apply -16v to the regulator and got -12v out so IC3 was good.
That meant Q3 or Q4 was probably bad but they didn't test or appear faulty. I ended up buying a pair of B647 & D667 transistors from eBay and replaced them (one is for the positive 12v rail, one for negative).
The board is labeled 647 & 667 but the schematic says 8050 & 8550 so maybe those are equivalent replacements...?
Anyway, the unit works!
Maybe this info helps someone else down the line.
