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]

On 9/28/2015 3:06 PM, bitrex wrote:

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.

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

 

[John S]

On 9/28/2015 2:20 PM, bitrex wrote:

On 9/28/2015 3:06 PM, bitrex wrote:
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.

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

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]

On 9/29/2015 2:27 AM, John S wrote:

On 9/28/2015 2:20 PM, bitrex wrote:
On 9/28/2015 3:06 PM, bitrex wrote:
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.

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

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?

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.