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I have a PMH 660 mixer, the amp module is damage. I repair amplifier module, I change R1,R3,R7,R8,and T1,T2,T3,T4.I check voltage on output of channel A and B, it's ok, and I feed signal to mixer. now channel A is OK, but channel B is "bum" sound when I increase the volume to 80% ( channel B is ok when I put volume below 80%) and the protect circuit is operate, could anyone help me please!
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First, maybe this: Disconnect the wires from the power amp to the output jack board. I believe there are triacs on the output board for protection. If your amplifier circuit was burnt up before, one of those triacs could have been damaged. So by disconnecting those wires, you can then clip a speaker directly to those wires. If that allows it to work correctly, change the triac.
If you replaced R7, then R51, and R52 could have been damaged, so check them. And do the same for the pairs of resistors around the other 0E1 resistors you mentioned. And T6,7,8,9 could have been damaged.
D5,6,8,9 are 15v zener diodes. See if any of those were damaged, and the resistors around them. ALl those are involved in the gate drive and could be causing excess current through a MOSFET.Education is what you're left with after you have forgotten what you have learned. -
Thanks!Originally posted by Enzo View Post
I will test diode zener, I measured the voltage on IRF 640 about 4 V and IRF 9640 about 6V. I change output wire channel A for channel B, it's still there, I think the triacs ok, and I change R44, R52, R45, R55 before. And I change T6,T7,T8,T9 with new one. I will change one by one from channel A to channel B parts in the gate drive.Comment
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Also remember, if one channel is now working well, you can use it to compare meter readings with the bad channel.
When those MOSFETs burn up, it is important to look at everything around them. Think about where current had to flow when the MOSFET failed.Education is what you're left with after you have forgotten what you have learned.Comment
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