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A friend asked me to look at his PMP 1280S. He was told no one would work on the Behriingers. He bought a new Yamaha but really liked this mixer. He had been given a set of speakers and apparently one of them was shorted and when he connected it, the output blew.
When I got into it, I found all of the output FETs were shorted and the 0.03 ohm sensing resistor was blown off the board. I got new parts and replaced them, but the channel still had -3.67Vdc on the output and the channel would not work. In the process of comparing the voltages between the working channel and non working channel, the probe slipped and took out one of the outputs on the good channel. I replaced it and the previously good side still didn't work correctly but only had about -1.04vdc on the output and would pass some signal.
I have a schematic and found that the drains of the three output, on both channels were not hooked together. On the previously good channel, the drain connection between T24 and T20 was missing (where the slip occured) so I connected it externally. It now amplifies, but I think there is some other small issue going on that I'm not going to worry about until I get the other channel working.
The original channel, with the blown sensing resistor was missing the drain connection from the L4 to T25, T22, and T23. I did connect it externally but the channel still has -3.67vdc on the speaker wires and the signal coming from the mixer does not appear on the gates of the mosFets. I'm sure the control circuit is shutting it down but I cannot find information about the 9001 controller and cannot seem to find the source of the imbalance causing the -3.67vdc on the output.
I did read a posting about the Behringer amp boards having a design flaw and wonder if the original failure caused more damage to an inner layer than just the drains opening.
Are replacement boards available, maybe a new power amplifier module I can retrofit into this mixer, or some other way to get this back up and running? Any help would be appreciated.
Current situation
Bad channel
T25 gate=-89.2, drain=-3.67, source=-89.2
T22 gate= 89.2, drain=-3.67, source= 89.3
"good" channel
T24 gate=-84.9, drain=-1.04, source=-89.3
T20 gate= 84.8, drain=-1.04, source= 89.2
When I got into it, I found all of the output FETs were shorted and the 0.03 ohm sensing resistor was blown off the board. I got new parts and replaced them, but the channel still had -3.67Vdc on the output and the channel would not work. In the process of comparing the voltages between the working channel and non working channel, the probe slipped and took out one of the outputs on the good channel. I replaced it and the previously good side still didn't work correctly but only had about -1.04vdc on the output and would pass some signal.
I have a schematic and found that the drains of the three output, on both channels were not hooked together. On the previously good channel, the drain connection between T24 and T20 was missing (where the slip occured) so I connected it externally. It now amplifies, but I think there is some other small issue going on that I'm not going to worry about until I get the other channel working.
The original channel, with the blown sensing resistor was missing the drain connection from the L4 to T25, T22, and T23. I did connect it externally but the channel still has -3.67vdc on the speaker wires and the signal coming from the mixer does not appear on the gates of the mosFets. I'm sure the control circuit is shutting it down but I cannot find information about the 9001 controller and cannot seem to find the source of the imbalance causing the -3.67vdc on the output.
I did read a posting about the Behringer amp boards having a design flaw and wonder if the original failure caused more damage to an inner layer than just the drains opening.
Are replacement boards available, maybe a new power amplifier module I can retrofit into this mixer, or some other way to get this back up and running? Any help would be appreciated.
Current situation
Bad channel
T25 gate=-89.2, drain=-3.67, source=-89.2
T22 gate= 89.2, drain=-3.67, source= 89.3
"good" channel
T24 gate=-84.9, drain=-1.04, source=-89.3
T20 gate= 84.8, drain=-1.04, source= 89.2
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