PL400 Backplane bring up problem

gtv2000

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#1
I'm doing the backplane on my PL400. I had previously done the control board and used the amp for a year or so with no issues. I converted the control board to full complementary. I'm at the stage where I have one row of transistors and installed the control board into the unit. All tests up to this point have been good. But after installing the board I am getting around 100mV on the right channel output, left channel is zero Volts. Power supply voltages look good.

If it makes any difference the dc protect board is installed and the outputs are connected to it, but no power is connected to the protect board.

Any suggestions on where to look? Thanks.
 
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gtv2000

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#2
When I first bring it up to voltage, the reading on right channel output is about 0.300 V, then it drops over about 30 second to 0.100 or so, then rises to 0.140 V and seems to stay there.
 

laatsch55

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#5
If it makes any difference the dc protect board is installed and the outputs are connected to it, but no power is connected to the protect board.


You mean the power to operate the DC protect board from the rectifier?
 

gtv2000

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#6
Well, fixing that shorting made the output voltage zero. But the bias voltage sits at 20 mV and doesn't seem to change with the pot. Both channels.
 

gtv2000

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#9
The output and ground for each channel was connected to the dc protect board, but not power. I just figured it was an easy way to position the wires, But it doesn't matter where I take the measurements now, off the test points on the control board or the backplane board the measurements are the same for bias. It's somewhere around 25 mV no matter where the pot is. It's like the transistor is not turning on at all.
 

gtv2000

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#10
I think I have the 2n5088s install into the wrong holes on the board. I didn't look at the photo closely and put them into the holes closest to the transistor.
 

laatsch55

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#11
That would do it..., while you have them unsoldered do a diode check on the junctions...
 

mlucitt

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#14
Pictures are a good way to help folks troubleshoot from the forum. Try to include high resolution photos next time so we can enlarge them. It gives us something to do...
 
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