Yamaha CP-30 muted notes and noise

I found this non-working Yamaha CP-30 at a recycle shop. Using my limited abilities, I was able to track the failure down to a transistor on the power board. I’ve replaced the transistor and the instrument works - sort of.

There are 6 keys near the bottom of the keyboard that play a muted sound, but only if you press the key hard. This is Piano II only. Piano I works perfectly over that key range. This synth has absolutely tons of redundancy so I’m guessing that 6 identical components failing is unlikely. The only thing that I can find that is common to all 6 keys is one side of the (I assume) divider ICs. It houses all the notes from that range (F# to B). This seems to be a common problem with this instrument so I hope it actually isn’t the IC and is more likely a capacitor or something common to these notes?

Speaking of capacitors, all of the 100uf 6.3v ones near the ICs are leaking. I assume they’re all dead. I replaced two (hoping to fix the dead notes) but nothing changed.

Also, this thing screams with noise. Everywhere I’ve read, people are saying that it’s normal for this instrument, but I highly doubt this much noise is normal. I think it’s more likely capacitors are dead everywhere and that is contributing to the noise. I’m reluctant to take the plunge to replace them all with tantalums or something more future proof until I can get all the keys working.

I was kind of hoping it would spring to life with that transistor fixed, but it more sort of limped into existence while wailing in white noise.