I checked them all even the fronts and did not find any leaking. I applied power and none of the channels will bias and they are all staticy and distorted. I must have several bad smd components. I dont know where to begin. The voltage is back from gate to source. All this came after I tried hooking up speakers. So obviously I still have the same problem. No components seem to be smoking on the board now, maybe because they have failed.
I still dont have any DC on the bridging terminals on front or rear so thats a good thing I guess.
I still dont have any DC on the bridging terminals on front or rear so thats a good thing I guess.
Soon as I started driving a signal something popped in the amp. The LR+ bridging terminal now has -30.67 vdc on it. The drain for Q410 (IRF540) has -30.65 vdc and the drain for Q411 (IRF9540) has -30.65 vdc.
I see a clean signal both sides of C314, nice waveform and clipping at high volume.
C412 has a clean signal on one side just like C314 but its different on the other side. When I touch the scope probe to the other side of C412 the baseline drops 3 divisions and the waveform is funny looking. Its like double stacked over top of its self if you will. That side of C412 also has -15.02 vdc on it as well and it does not amplify like the other signals. It only goes 1 divisions before showing clip where the others go 3 to 4 divisions before showing clip.
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I replaced the A06 and A56 in that channel. Upon powering up the amp started drawing alot of current. I removed the output fets for that channel and the IRF540 was shorted. I replaced the IRF540 and repowered the amp leaving out Q411 which is the IRF9540. The amp powered up fine. I tested the solder pads of Q411 and I am only getting +14 vdc on the gate and +30 vdc on the source. Why am I only getting +14 vdc to the gate? All the other gates have +/- 30 vdc as they should. I think my problem is some how related to this
The gate voltage isn't going to be like the channels with all of the components in place. You've removed the outputs which opens the feedback loop.
As a side note, R452 should be getting extremely hot with 16v across it. If it's not so hot it's on the verge of desoldering itself, it's likely defective.
As a side note, R452 should be getting extremely hot with 16v across it. If it's not so hot it's on the verge of desoldering itself, it's likely defective.
The IRF540 is in place because I replaced it. The only thing not in place is the IRF9540. R452 does have 16v across it and it does get hot. I already replaced it once so I am sure it is fine.
On another note when I had the 540 out of circuit its gate pad still had -30 vdc like all the others.
On another note when I had the 540 out of circuit its gate pad still had -30 vdc like all the others.
16v is enough to burn it out again. If it stops getting hot and has 16v across it, it has opened or drifted in value.
The drive circuit is trying to compensate for any DC on the output terminal. Just a few millivolts is enough to cause the drive circuit to apply the maximum possible drive voltage to the outputs. If the slight DC was negative, it would have driven the top side FET on. There would not have been any reason to drive the negative side FET on so there was no drive voltage applied.
Does the amp draw excessive current or have DC on the bridging terminal for this channel if you reinstall everything and lift Q405 and Q406?
The drive circuit is trying to compensate for any DC on the output terminal. Just a few millivolts is enough to cause the drive circuit to apply the maximum possible drive voltage to the outputs. If the slight DC was negative, it would have driven the top side FET on. There would not have been any reason to drive the negative side FET on so there was no drive voltage applied.
Does the amp draw excessive current or have DC on the bridging terminal for this channel if you reinstall everything and lift Q405 and Q406?
The black probe on the emitter solder pads of Q405 and Q406 while they are out of the circuit?
With Q405 and Q406 out of the circuit and black probe on their emitters this is what I measure.
Black probe on emitter pad of Q405 red probe on base of MPSA06 -4.86 vdc
Black probe on emitter pad of Q406 red probe on base of MPSA56 +20.70 vdc
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