Interesting Marantz 2238b Hum Issue

[waryan]

Hi folks. This is a good one. I’ve recapped the 2238b with all new electrolytics on the tone, phono, and amp/PS boards. On Aux I have a serious hum that rises with the volume. Now, the interesting part. If I am playing through Aux, I hear the hum. When I stop playing, 20-30 seconds later, the hum disappears. The moment I hit play on the source feeding Aux, the hum reappears. This is repeatable. This occurs in both channels and both A and B speaker sets.

I have to think that this is the Amp board acting up when it receives a signal / current. Once it dissipates, everything goes back to normal. Does that make sense? Anyone know of especially noisy or failure prone transistors in this unit? I appreciate any insight. Thank you.

 

[dimanag]

Did you try a diferent source and/or diferent interconect cable?

 

[waryan]

Did you try a diferent source and/or diferent interconect cable?

Yes, multiple sources and multiple interconnects and the issue persists. Thank you.

 

[omegaman1954]

check for a loose or bad ground

 

[El Rubio]

I agree with ground issue. A poltergeist dropped a needle nose plier into a receiver I was aligning once and one of the issues was a slight hum. I found a burned trace on the PCB. It was very thin and didn’t make a large burn mark. First order, if you haven’t done so already is to confirm cap polarity. I have seen boards marked incorrectly, and the occasional mistake on my part. Good luck with it.

 

[jhjove]

Was the hum present before your overhaul?
No, then I'd check your work on the e-cap R+R for correct polarity.