Hello i have just got a peavey microbass and when i switch it on it hums very loud, iv taken it apart and one of the chips is dammaged it is slap bang in the middle of the board with 5 terminals going into it, and is screwed to what seems to be aluminium block, can i get a replacement chip??
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Most of the time amplifier hum is caused by the outlet that it's plugged into, maybe no ground or there's other appliances on the same circuit causing interference? And sometimes it's as simple as a little internal feedback, certain C notes on the Guitar cause distortion with tube amps, the best fix is a $100 power conditioner like made by Monster cables or others.... hope this helps?
Likelly the TDA7293 chip in the power amp has failed. It shorts to one power rail and drags the power down where it hums... this CAN damage the speaker if left on. Verify the problem and replace the chip. Slight chance there are bad electrolytic filter caps but those are easily spotted.
i) Disconnect one lead of loudspeaker & insert an open-ended guitar cable into headphone socket.
ii) Put a dc voltmeter across open end jack then turn Frontman ON for a few seconds.
iii) The reading should be about 0volts - if the voltage is high (27v), then it is likely that the PA chip TDA1514A has blown.
iv) If,however, the voltage is correct in iii) , then reconnect speaker & put guitar cable into the POWER AMP IN socket & connect other end to guitar...Turn on briefly, if there is still hum then fault is in the output stages & will require chassis removal to solve.
If you switch on the amplifier, do you hear nothing at all?
Or do you hear low level noise or hum out of the speaker? Don't know if you're technician.
If the tubes are glowing, you can measure the high voltage.
Check also fuse 3 and 4, thats the neg. voltage -27V and -14V.
You have a bad ground probably inside the amp , you need a on hands Tec for this one. I bet its not to serious , about $65.00, is it worth it to ya all tho I don't know your area , but its been my exp.this would be a fair price most any where. good luck DFD
There should be an 8 pin IC close to the input jack that will be marked 4558 or 4560. This is an Op-amp Ic that is the most likely cause of the problem. Replace that IC and report the results here.