Behringer PMH660M Powered Mixer Fix - Blown Outputs Repaired - Warning: Hazardous voltages!!!
This PMH660M worked well except for the amplified outputs were dead. I found that Output B had shorted FETs. Removing them from the amp module brought Output A back to life. The overcurrent sense circuit on Channel B was causing both channels to mute since the current sense circuit for both channels are OR'd together, which in turn disables the FET drivers. It turns out that both current sense resistors on Channel B (one on each rail) were open. Replacing both the FETs and the 0.1 ohm current sense resistors on Channel B brought this unit back to life. In additon, some dirty switches needed some De-ox, but otherwise all is good. I found the schematics by Googling "PMH1000" (rev D) that contained the amp section that matched this unit. Also, when servicing this amp/power supply section, it's easiest to disconnect the two sides (Two AC wires. cable connector and ground lug) to better access the amp and give yourself more cable slack. It's easy and fast. I found this out the hard way.

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