On power up there is a loud humming even with volume at 0
I have a Yamaha G100-212Guitar Amplifier. It didnt work when I first got it. I replaced both of the power output transisters.Powered up and played the guitar for about 5 minutes. Then I turned it off and I turned it on again there is this loud humming noise.
I have the schematics. Any suggestions whats causing the noise?
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Why was it on for over a year :D
Has anyone replaced the fuse? In the service manual I found it has to be only 2 Amps!
Okay let's solve the problem. The power transformer was overloaded which caused the broken winding. It is still overloaded what can be heard by the hum sound.
First thought was to check main capacitors or better just replace them! If the hum gets louder, they might also become warm.
Check voltages after bridge rectifier and smoothing circuit. They should be +/-42 V (TP3, TP4) and +/- 16 V (TP5, TP6)
Let me know which of them is faulty
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.
Make sure you have a ground prong on your power cord. Most input jacks nowadays are closed circuit. They have a switch built in that won't allow any sound without the cord plugged in. You may have a damaged jack that will give you a loud hiss, a loud hum or crackling depending on what volume your controls are set at.
try placing your ear on the speakers, adjust the volume control up and down several times, you should hear a humming sound that goes up and down. if not problem with the stage before the amplifier, that is the sound processor. if you dont hear the hum. problem with the amplifier and speakers, including the sound ports or jack. dissassemble the unit. look for loose connections from speakers to amplifier.
the buzzing is indicative of an open ground connection, check the cord by substitution or with an ohm meter, if the cord is good look at the connections to the jack inside the amp ( im guessing you built the amp from a kit). Is this a solid state amplifier? Tube amps have lethal votages and should not be experimented on without knowledge of electronic safety. Also if there is more than one input to the amp try plugging the guitar into another one and see if its still the same.