> I just purchased a damaged second hand a-136 Waveshaper. Looking
> at the PCB I think the module has had it's power conection hooked
> up the wrong way around at some point in it's life. The chip
> (75H21EK LM324n) that is hooked up to the amp knob via a yellow
> wire has a black burn mark under it and on the reverse side the
> solder is slightly blackened, as is the PCB.
>
> I guess the chip could be blown The rest of the module looks fine.
>
> How it sounds All of the knobs still have an effect although the
> module only seems to produce sound in the negative range and the
> ext.level CV inputs don't seem to do anything. It only cost £20
> and still produces some nasty sounds!
>
> Any help would be great :)

I'd recommend to replace the two quad operational amplifiers LM324. They are
low cost parts and should be available for much less than 1 US$.

Best wishes
Dieter Doepfer