help needed with Crumar Multiman pitch adjustment control

[pierrer]

Hi,

I am experiencing trouble with the pitch adjustement pot on my Crumar Multiman string machine : when i first got it it used to allow me to tune the synth over several semitone; now it still changes the tuning but ever so little, well under a semitone. Any idea what's wrong?

Here is the schematic for those who want to have a look:

 

[PRR]

Could they draw that any more mixed-up? (I guess they could.)

Check/replace the pot, of course. It can be ohm-metered in-circuit.

Replace the 220pFd marked "10", in the wiper-path of the pot.

 

[pierrer]

i have replaced the pot, and C10 as well as all the other 220pF caps whilst I was at it. Problem persists.

I thought it could be something wrong with the chip, but I just looked up the datasheet (see below) and i don't think it's that anymore: it's simply a clock that comes on it's pin 2, and you speed/slow that clock slightly to fine tune the synth... so i'm assuming it's the slowing/speeding of the clock that is not done over the expected range.

So i'm thinking it could be the transistors maybe, what do you think? is there a way to test them without taking them off the board?


http://synthdiy.com/files/2001/mk50240.pdf