Proton AP-1000 volume related issues

[MiauwMaster]

Hello everyone.

I have a very nice proton preamp but lately it has been showing a very annoying problem. Every now and then, out of nowhere, the volume opens up to a very, very high level and after a second or two it pops back to normal.

I've checked the volume pot (it is a alps 10kbx2) and it seems to be alright. tiny bit of noise on the bottom end when turning it but nothing weird so I suspect it's something else. Now I've repaired some amps, cd players and speakers but I'm not sure where to start here as this is the first preamp I'm trying my hands on.

Now, to my question: Is there anyone who has had a similar problem with a preamp (proton or not) and where should I start looking for issues?

Any help is greatly appreciated as my house is cut-off from my main audio set until this problem is fixed as I don't feel like blowing up my speakers or going deaf if my preamp decides it should open up completely at some point.

thanks in advance!

 

[ryuuoh]

That's a pretty complex preamp. I'd suspect the active amp, where the volume control is.

 

[MiauwMaster]

That's a pretty complex preamp. I'd suspect the active amp, where the volume control is.

Thanks! Luckily I have a service manual. I'll look into that section first.

 

[MiauwMaster]

Well that was easy. While checking components I found out it was actually a bad cable between the volume pcb and the main pcb. So after soldering a new cable in place everything is fine again.