Sequential circuits samplers

So I just bought a P2002 from ebay, and unfortunately, it has some
issues. Voices 7 & 8 aren't working properly. That is, if I hit a key
8 times, on the 7th and 8th times, the sample doesn't play.

I've determined it isn't the CEM chips because I can program a high
resonance filter sweep and hear a swept sine wave on voices 7 & 8.

Does anyone know off-hand what the problem might be? If so, is it
something that I or a local synth-tech might be able to fix?

I'm hoping it some other kind of bum chip that's easily available from
Wine Country.

Also, does anyone have experience with the SONY MPF520-1 drive? I'm
getting the "Lh" error, and the Sony drive seems to be the most
readily available and relatively inexpensive.