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08-27-2009, 10:34 AM
| #1 |
| Junior Member  Join Date: Sep 2007 Location: Australia
Posts: 2
| Fender FM 212r low level hum
With no inputs plugged in get a low level hum. Found if I plug a jack in either J1 or J2 hum disappears but get a bit of very low background noise normal to amplifier. On the schematic the switching on the Jacks goes to a Mute circuit. I have two units here and all voltages seem to be near identical but the second one behaves correctly. Even though power electrolytic caps check OK replaced them anyway. Can anyone explain the operation of the Mute circuitry so I might be able to troubleshoot further as it has me pulling my hair out. http://www.fender.com/support/amp_sc..._Schematic.pdf Thanks |
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08-27-2009, 04:10 PM
| #2 |
| Member Join Date: Apr 2009 Location: CT
Posts: 34
| FM 212R Hum
Unless there is a cold solder joint on the printed circuit board, you probably have a bad input jack. It should be making connections when there is no jack inserted to stop the noise. I would replace both of the jacks (J1 and J2) since you will have the amp apart. Steve |
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