Marantz 4140 Bass thump issue

[nolannnniah]

So...I started cleaning the x2 & x4 selector pot in the back (S004), and the other pots & push button switches...cleaned up any extra cleaner and let it all dry out. Hooked it all back up, fired it up and waited...No issues...or so I thought. I started turning it up little by little. Then I heard a screeching sound-I killed power immediately-relay did not. I blew some air in around everything and waited a day...thought there might be some excess cleaner I missed. Next day I powered it all back up. Now I have a hum through all channels, even if I have volume down-hum does not get louder with volume getting turned up-just constant. Selection of input has no effect on the hum. As soon as speaker selection is pushed in, the hum is there. So it seems now I am worse off then when I started...I checked off sets on amps, main power board and checked to see if I could see if any connections were loose, cracked or "hanging" on. Nothing, all readings are good...Slightly frustrated and about to use it for a door stop...

 

[nolannnniah]

Hi all, question...Would a old/bad resistor feeding in to a transistor (on the power supply for the unit) cause a hum in the speakers? I got it back up and working again, but with the hum.
Thanks,
Nolan

 

[Doug G.]

Probably not. Hum is always due to 60 cycle (I assume you mean 60 cycle, or is it 120 hertz?) AC getting into the DC circuits which will be something in the filtering circuits like capacitors or diodes. There are other capacitors in the power supplies to filter voltage to the lower volatge circuits like the pre amp/tone controls too.

Doug