another BSAIBII problem

[Steben]

Voltage readings seem fine to me (trust me: they are fine), yet no sound at all.
If I let something hit the pcb (like my finger  ) and there is a fizz, all works fine: gain pot makes the sound go into distortion, volume pot works and the tone control makes "foozz" to "fizz". SO the only problem is there is no guitar signal. input is short circuit to guitar cord, so it must be a cap or so. The first parts to look at are C4, C9 and C12 I guess.