Issue:
- Distortion/crackling when key is pressed, seems worse at lower frequencies.
Boards:
- White board = main power amp and power supply
- Green board = digital processing
Initially I saw a number of leaking SMD caps on the digital board, that actually shorted out the board power rails and burned the PCB. Caps measured as close to 0uF.
These bad caps were replaced, carbon was scraped away, but the problem was the same. Kind of a lesson to not pepper a bunch of cheapo useless caps around (there is plenty of capacitance on the power supply board).
The power supply board was checked, all caps are good.
Power amp pins were re-soldered. Pushing on any area of the power amp or digital board doesn't affect the issue.
Clues:
- distortion heard more when certain keys are pressed (frequencies)
- same distortion heard in headphone jack
- distortion present in recorded/demo sounds, so not caused by keys themselves
- distortion seems to mostly go away after 10-15min of warm up
If the main amplifier chip is at fault, its not worth replacing. But if anyone has any other ideas, please post.
What it sounds like:
https://youtu.be/YuqCoRGCiMgSimilar thread here:
https://www.eevblog.com/forum/beginners/fixing-a-cvp-85-piano-unknown-schematic-symbols/ (possibly need to replace more caps)