help troubleshooting a centura

[davebolden44]

I put together a centura a few weeks ago, at first it worked fine. then it slowly started getting this cloudy background noise that sounds like a needle running on a record player. when I turned the gain knob it seemed to really have an impact on this noise. then the gain knob would work the first 3/4 of sweep then audio would cut to a wisper after that. it seems the center lug of the wiper on the gain knob is hooked up to the power supply and distributes voltage to the second half of the first ic and its surrounding circuit. at first I swapped the gain knob out to no avail. I have been tracing through with my scope and things get a little wiggly at the start of the second ic. I have little experience troubleshooting this kind of stuff and would appreciate some opinions. I dont think I burned anything up soldering I was quick and neat with that.

[Stevem]

It would be great if you could post a schematic, but in general many times some simple voltage checks will pin down a leaky / bad ic chip.
Finding some level of the D.C. Power supply voltage on a input or output pin of a chip would be one indication.
I never build anything that uses chips without using plug in sockets to save the board traces from distruction should I have a chip fail!

[davebolden44]

Thank you for the reply. I will mess with it when I get home from work and check the voltages. I have never messed with this kind of circuit before or used any ic's. Appreciate the advice. I will try and post a schematic also.

[M Fowler]

Here is the instructions complete with schematic.

I have a complete Centura plus 3 kits if you need some info from mine.

Centura-Instruction-010417-Doc.pdf

[davebolden44]

Awesome that helps a lot. I just built it from the klon schematic and pictures online. It worked flawlessly for a while and then just on and off it would be fine. Any tricks to pinpoint the component in question will be great. I will check voltages and check over my wiring again.

[davebolden44]

a simple voltage check is where I should have started, but I wanted some practice chasing signals with a scope. the second ic was where my scope started getting wonky and sure enough there is a negative voltage on pin 7 which is the output. I think it is pinpointed because all other voltages check out. 80 cent part from mouser. thanks again guys.

[martin manning]

I think you have it too. That pin should be at 4.5V.