Further MS2000 synthesizer problems

[bitrex]

Here's the service manual for reference:

http://www.loscha.com/scans/Korg_MS2000_Service_Manual.pdf

I replaced C109 with a 100uF electrolytic temporarily, and also found
that the power and ground planes were shorted together. Common mode
choke L10-L12 had apparently burned and shorted, so I've temporarily
replaced it with jumpers.

The +7 and +5 rails are up and running now, but the 3.3 volt rail is
still down. I measure about 8.6 volts from positive to negative across
C109, but I'm also seeing about 8.7 volts from the ground terminal of
C109 to the ground fin of regulator IC7.

[bitrex]

There's no continuity between the top of C25 and where C50 would have
been. Guess L13 is smoked as well.. :(

[John S]

The schematic shows that L10, L11, and L13 are NU (Not Used). L13 is
replaced by a jumper. Is the schematic for your unit accurate?

[bitrex]

You're right. I believe it's accurate, I was just being dumb. The
common mode choke was just 2 windings - it was scorched and shorted. I
cannot find L13 anywhere on the board. Still, there seems to be a
continuity problem somewhere as the buck switcher is not getting an
appropriate input voltage.

I think I'm first going to take the other poster's suggestion,
disconnect the switcher completely and see if I can get the logic
working off a bench supply, as if I can't get it operating that way then
this exercise is really for nothing.