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Old 25th April 2005, 07:05 PM   #1
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Location: scotland
Default noise after fixing guitar amp?

Hi,i bought a small Fender guitar amp at a car boot sale,i was told it was perfect,as new,got it home it was knackered basically.Looking into things further i noticed there was a 2 inch long crack in the circuit board!I have managed to bridge with solder all the parts that were interrupted by the break of the circuit board.When i was taking the circuit board out of its postion i tried to unscrew a hollow nut that was holding down the main earth to the inside of the amps chassis(o-ring connector at end of earth wire,nut tightened down on it)but when i tried to unscrew this nut it kept turning and wouldn't loosen,so i was left then with an insecure earth connection,i made this more permanent by soldering it in place.So both channels on the amp now work great but im now left with a constant electrical buzzing through the speaker?This has only been since i soldered this earth more securely?or with the handling of the circuit board could it cause this?Anyone any suggestions?thanks!
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Old 25th April 2005, 07:16 PM   #2
Netlist is offline Netlist  Belgium
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Since that earth connection was tightened to the chassis, you could measure with an ohm meter if you have about 0 ohm's between that wire and chassis.
Do you still have hum with all volume controls to 0 and/or inputs unplugged? If not, one of the wires or PCB traces you repaired could be faulty.

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Old 25th April 2005, 10:54 PM   #3
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Yes the noise is there all the time,with all volumes down.
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Old 26th April 2005, 05:18 AM   #4
Enzo is offline Enzo  United States
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WHAT Fender amp do you have? It will make it easier to get out the proper schematic. Make sure the filters are doing their job, one might have cracked its solder. MAke sure you did not alter the grounding arrangements when you repaired hte crack.

If the board was cracked in two so the parts were separate, just repair with jumpers, but if the crack goes from an edge out into the center somewhere and ends there, drill a smal hole at the end of the crack as a strain relief so the crack does not grow.

If you repaired all teh obvious broken traces, go back and look for traces that seemed intact but crossed thre crack. They may have tiny cracks acrosss them.
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Old 26th April 2005, 09:13 AM   #5
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Join Date: Apr 2005
Location: scotland
Hi,the amp is a Fender Frontman 15g,i have the schematic but i can't send you it,you probably have it anyway ;-) I just find it strange that this buzzing only started when i made the main earth wire(the one that comes from the main power plug at the rear where you plug in the power cable)more secure by soldering it to the plate it was originally just screwed down by a flaky,hollow,brass coloured nut.I don't know enough about what you mean by 'altering the ground arrangement' when i was bridging the traces that were split.I was as careful as i could be when soldering,solder seems to have gone where i wanted it,what about cleaning the circuit board?There are small traces of flux from the flux and solder i was using,would this flux paste that is left between say two solder points,would this cause the electricity to arc between two points?If you know what i mean.The way i checked the circuit board for splits in the traces was a i shone a strong torch from the rear of the board,then i could see splits easy.I've also taken care of the crack,it did start at the end of the board and worked its way across it,the crack ended in the middle of knowhere away from any traces so i just buried the solder bolt into the end of the crack for a second or two to seal it so to speak,thanks for your help so far!
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