Shruthi 4PM - filter tuning issues

Hi, I’m new here.

I just bought a 2nd hand Shruthi 4PM - the previous owner was selling it off cheap because he said there were some calibration issues with the filter and it wasn’t quite working correctly…but it was so cheap I figured it’s going to be pretty awesome anyway (and yes, yes it is!).

Anyway, I’m not quite sure what’s going on with it or what to look for - it works fine otherwise, but the calibration/filter tuning is way off. When I do the self-oscillation test I can’t get it even close to playing the right notes. Feeding it two MIDI notes just a semitone apart (like C and C#), the actual sound is over an octave higher with the latter; if I play an octave like suggested, the higher note is several octaves higher in pitch (or just erratic whining when it goes high enough).

I’m fairly new to electronics, can solder with a shaky hand but would need some assistance locating the part(s) that can cause this kind of behaviour. Thanks.

Post a picture of the boards. It looks like it’s an assembly mistake rather than an incorrect calibration.

Hey, sorry for the delay. Here are the images…

Can anybody have a look at this? Bad internet connection here.

There is some slightly wonky soldering here and there(on the digital board, but that seems to work?), but nothing too bad… Could you post a backside picture of the filter board?
Edit : Also some quite…diverse resistors that were used, one of them looks like a 0.5W or 1W resistor…

i checked a lot of the (different) resistors used. I came across these ones in the picture. R29 and R31. They are supposed to be 1.0k … i don’t know what kind of color coding these ones use but i can’t make anything but 42 ohm or i read it in reverse?
But anyway they are in the resonance circuit so this could be something.

If you are handy with soldering you could solder them out and measure them.
You do know that the trimmer for setting the range takes 25 turns from one side to the other?

Thanks. It seems likely that those two resistors are indeed wrong (I think they’re 32 ohm - what looks like yellow in the photo is definitely orange in the real world), but the color bands are so close together that I wouldn’t be surprised that whoever built this made the same mistake!

And yeah, I know about the trimmer. It never comes even close to anything sensible, though.

I’ll try to replace those two and report back…