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Fender bassman 500 pot issues?HELP!!!!


highwayone
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Just bought a virtually new amp but the push/pull function on the tone controls seem to have an issue. When I pull the bass know out(which gives it a boost) the amp makes a loud buzzing sound and the volume of the instrument virtually disappears. If in then switch it off and back on it works fine again. Any ideas what the issue might be? The seller will take it back but I like it and git it for a very good price so want to keep it ideally. Thanks.

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Without finding a schematic for the amplifier, I will make an educated guess that the boost circuit is a simple capacitor / resistor combination that is engaged by pulling the potentiometer out. Some possible faults in no particular order:[list]
[*]defective potentiometer - it has a poor internal connection when pulled out
[*]defective solder joint on one of the potentiometer terminals
[*]defective solder joint on the capacitor and or resistor used in the 'bass boost' part of the circuit
[*]defective capacitor and or resistor in the 'bass boost' part of the circuit
[/list]
Re-reading your description I am tending towards the first fault in my list. It may only be contact oxidation and you might even get a fix by squirting some contact cleaner (e.g. Servisol) into the afflicted potentiometer.

Edited by 3below
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I tried to find the schamtic for this but its not on the Fender site. If you have it post a link.

If the buzz is a bit like when you have guitar lead not plugged in then my bet is that either the pot/switch is damaged internally, or the component that the pull knob bypasses/includes is damaged or has a bad joint. Try wiggling the knob side to side to see if it is the pot and give it a bit of a tap around the cabinet area to see if a bit of vibration triggers it. Control pots often get damaged by handling in and out of cars etc.

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