Rockford Fosgate T30001bd

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Strange things....
i replaced U300 again as well as Q313 even though the transistor measured ok.
same thing, pin 5 of U300 has -5.30V.
without U300 in, i also removed R303 and D1 and there is no voltage on pin 5 (in the pcb pad of pin 5).
Now, with D1 soldered back to the circuit, i still have no voltage on pin 5 pad.
But as soon as i solder back R303, i get around -13V on the pad of pin5...
 
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Yes i do.
In the mean time, i did mount the output fets on to do some testing.
The amp idles fine, i do have a 105Khz square wave on pin 2 of both UC 3706 (although not perfectly clear), and no dc voltage on the output terminals.
There is no output, only a noise when i tested with a speaker. (it swings between 0.9 and 1.5VAC)
After testing the pre amp section, i found that most op amps had DC on their output pins.
I isolated them from the regulators and i only powered the pre amp with -/+12V from an external source.
It works fine, the pots are responding as well as the switches.
There is a nice clear 100Hz sine wave on pin 1 of U107, and of course no DC.

However, when i removed R300 to check whether pin 1 of U300 gets low, i noticed that C355 that i had replaced earlier, had swollen.
 
After replacing a leaky D37, i fed the amp at R300 removing C355. There is a loud mid to high frequency hum, but on the background i can hear the test signal (100Hz) getting louder as i increase the gain.

where should i check to eliminate this hum?

When i soldered back C355 and fed the amp from the RCAs, there was no 100Hz sound, only the same hum. This is not a problem, i can easilyreplace all 8 op amps.
 
nothing changes with a different source.
i replaced all 8 op amps in the preamp section but i still dont get any output, only the loud hum.
Here is what i get at U300

pin 1 1.6
pin 2 0.01
pin 3 0.06
pin 4 -8.88
pin 5 1.54
pin 6 1.54
pin 7 1.54
pin 8 6.00

if i lift R300 and i inject signal to one end, i do get some signal on the output, but the hum is still loud.
However i noticed that the output swings between -2V to 0VDC.
First pic is what the signal looks like at Pin7 of U301
and the second one at pin2 of U401 (it is actually before and after R309).
Exactly the same applies to pin 7 of U302 and pin 2 of U400.
 

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Did you ever find the break in the feedback circuit? Because you said you checked traces, BUT the BDOUT is tapped BEFORE 'L400' so if you hardwired the connection on THAT side of the choke and there is still a break in the choke that output will never couple with the other phase which has it's own respective ties to the feedback system.

Perry is right, you can't ignore that break. I would check L400 to make sure NONE of those wires are snapped near the PCB, i've seen that on a few of these. The breaks like to hide sometimes under the glue too.
 
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