Well, I got the new SSM2120 chip today and was able to replace the old one without too much difficulty. The chip is actually just to the left of the one pointed to in the photo from SC, and was a little tricky because it is almost completely covered by a circuit board above it. Anyway, I put in the new chip, fired it up, and ... I still have the same problem: no sound at all from the unit with the compressor engaged.
On top of that, I've discovered that the wah does not seem to work, either. If I switch the wah in, no matter what I set it to, when I pick a note, all I get is a low buzzing noise. So, no compressor and no wah.
I'm not sure what to do with this. Part of me wants to make an issue of this with the eBay seller and try to return it for a refund. On the other hand, it sounds good, I most likely wouldn't use the wah feature anyway, and I can probably live without the compressor. But then if I ever sell it, I'll have to sell it for a lot less than I paid for it as I'd have to sell it as damaged goods to a degree. I'll have to think about this...