Electronics 2000

Hi, I need some help please with a potentiometer.

The problem is: I am building a synthesisor from a kit (a clone Roland drum machine). One of the voices (bass drum) has a number of parameters e.g. level, distortion etc. which can be changed via potentiometers. One of the potentiometers does not work i.e. no effect on the sound. I have checked that the potentiometer is the correct value and have checked that it is working correctly (i.e. the resistance checks out when I 'turn it up and down'). FYI the rest of the bass drum seems to be working/sounding fine.

Can anyone tell me how to debug this problem, I don't really know how to approach this. I had another problem on another part of the synth where I followed the signal around the circuit with an oscilloscope until I found the fault. However, I am not really getting anywhere with this approach.

I am not very experienced with fault finding and any help/pointers would be fantastic!

Hello. This could be quite a simple problem - you say that you are building it from a kit, and that most of the drum synth and the potentiometer itself work. Try checking that all components are soldered neatly onto the board, and that there are no solder bridges between tracks. Check that all diodes, transistors, and electrolytic capacitors are inserted in the correct way (i.e. not reversed). Check that all ICs are inserted correctly. Check that you have the correct value components in the correct places (I remember once putting a 22k resistor where a 2.2k should have been, and it took me a long time to find my error). Check external wiring. Hope this helps.

Ok thanks, I was rather hoping there was a smarter way of checking. All the components appear to be the correct value and polarity. Any ideas?

On to the next stage. Have you got a circuit diagram? That will be the most useful thing. If so, concentrate on the area around the drum and the potentiometer, and see if you can track the signal through the circuit with the scope until the signal fails. If you can do this, the number of components that may be faulty around the failure point should be small! Look out for cracks in the PCB tracks, and if the circuit diagram shows voltages to be expected at different points, check these.

Well David you sound like you know what you are talking about welcome to the forum both of you... interesting project.
Diagrams and pics needed.

Tar&stuff.