Today started working on Korg 05R/W module number 2 of 3. This unit has no audio output. During one of my audio tests, I did get extremely faint audio for a brief moment, but then it ceased.
This one had a different board revision (KLM-924) than the other units I have (KLM-924A AND KLM-924B).
This particular board also has an odd bodge-diode thing going on. On the subsequent revision board, it looks like they added a transistor (ZD2) near the same location. I'm assuming this may be a factory job if it was to correct some sort of issue with the original board design. Unless this was some sort of aftermarket repair attempt?
Things tested / worked on so far:
- Tested volume pot; seems to be reading okay.
- Replaced through-hole capacitors; original caps were a bit under capacity, but still within spec, so probably not an issue.
- Checked and didn't find any broken solder joints; reflowed the 1/4" output jacks just in case.
The board has minor corrosion in places, but haven't found any broken traces (yet).
Other than a moment of brief extremely faint audio, haven't gotten proper audio output. I'm going to keep checking traces and for shorts. I'll also probably start removing the aluminum SMD caps and testing those. I'm also wondering if it might be worth doing a general reflow on the SMD components to make sure everything has proper joints.
One last item, I did have an original Korg adapter for this unit. It's supposed to output -12V, but it's outputting a whopping -17.5V. Good thing I haven't been using it!