Korg Synthe Bass SB100

[The Dude]

I've got a head scratcher. I've got a Korg Synthe Bass SB100 vintage analog synth on the bench that's driving me in circles. The schematic, while difficult to read and has split pages, is here:

https://manuals.fdiskc.com/tree/Korg...0Schematic.pdf

The unit has no output. Power supplies are all tested and correct. There are 3 parts of the thing that are drawn as blocks. They are sort of primitive IC's- a plastic encapsulated circuit board made of discreet components with no schematic for the blocks. I cracked open the one marked TS100080, which I believe is a VCA, because I have signal in at pin 3, but no output at pin 7. The signal at pin 3 is audio (can be seen on a scope and heard with a signal tracer). Of course the TS100080 is no longer available, or I might just replace it. I did check all of the components in the thing and could find no obvious problems. My question is this: Does anyone see an external connection/signal/voltage to the TS100080 that may cause it not to function, or do you think my problem is in the module itself, or am I looking in the wrong place all together? Pin 7 of the module is the output and there zero output on that pin.

[dmeek]

Is the TS100080 potted in epoxy? If not please post photos of both component and foil sides.

The TS201012 is a VCA Here is it's schematic keio-TS201012 VCA.pdf

[The Dude]

I have output on the TS201012, which feeds the TS100080 pin 3 (see schematic), so I'm relatively certain it is working. Where I loose signal is between the TS100080 input and output. The output of the TS100080 goes directly to the volume control and output jack, so according to the block diagram in the schematic, it should be the VCA.

Another odd thing: According to the schematic, the part should be TS100080. However in that location I have a TS200080. Possibly a revision? It looked original and to my knowledge the synth worked with it prior to failure. Do you have a schematic for the TS200080 or the TS100080? That would help immensely. I suppose it's possible that someone installed the wrong module, but it doesn't appear so. Module schematics would help figure that out.

I'm adding a pic. You'll see two "black boxes" and a satellite circuit board between them. The board between is the TS200080 (referred to in the schematic as TS100080) and used to be covered like the others. I broke the plastic off so that I could test individual components within and scope through the module, which is difficult without a schematic. I can't send pics of the solder side of the module at the moment because I soldered it back in for testing.

Also, in answer to your question, no- they are not potted in epoxy. They simply have a plastic "lid" glued over the circuit board. Relatively easy to remove. And, thanks for the help!

[dmeek]

The only other schematic I have is the TS200011 VCO I got them from http://www.colinfraser.com
If you can post a photo of the foil sides and a few close-ups of the component sides, I can draw the schematics for both. These would be fairly easy to do.