Firstly let me say I have a limited understanding of electronics. I kind of understand how each component works, but how they interact is beyond me. If I can find a bad part I can replace it, but that is about it
I picked up 2 Korg M1s at an auction, and luckily one of them work (except the buttons needed replacing)
The other one would not power on at all. I swapped power supplies and it worked fine, so decided the issue is the KLM 1267 power supply board.
Having in the "bad" power board plugged in, but not connected to the keyboard, I was getting voltage at 5- and 5+, and was getting voltage at -12, but was getting low or no voltage at +12.
I figured the likely problem was the capacitors, so I replaced C18, C19, C20, C21, C22 and C23 and there was no change in the voltages.
I started testing for resistance around both boards to see if I could determine where a difference was between the two.
I finally checked both sides of the D6 diode.
On the good board, I got .3 one direction, and .5 when I reversed the positive and negative leads.
On the bad board, resistance would almost drop to zero, then start rising again getting to 50-60 (on the 200k ohms setting)
I just tried to double check things, with power to the bad board, but I am not getting any output voltage, 5 or 12.
Any ideas where the issues may lie, or what I can test to determine what components might be bad?
thanks
-James