This amp is pulsing in the power supply.
The redlight comes on, but it pulses on my amp meter of my supply.
1 amp to 10 amp back down to 1 amp over and over.
A few of the rectifier legs were broken, I dont think they are defective but the legs are weak and I want to change them.
Could some bad drivers in the power supply cause this? Its like the amp is starting up over and over.
All the outputs were missing so I replaced them and they are in the right spots.
I replaced a copule of bulding caps in the feedback area.
I replaced a missing thermistor.
I replaced a missing resistor.
There was and MPSA56 in the power supply region with a broken leg and the other 2 were touching each other right next to the LM339.
Wondering if some of the other drivers could have been affected by that?
The redlight comes on, but it pulses on my amp meter of my supply.
1 amp to 10 amp back down to 1 amp over and over.
A few of the rectifier legs were broken, I dont think they are defective but the legs are weak and I want to change them.
Could some bad drivers in the power supply cause this? Its like the amp is starting up over and over.
All the outputs were missing so I replaced them and they are in the right spots.
I replaced a copule of bulding caps in the feedback area.
I replaced a missing thermistor.
I replaced a missing resistor.
There was and MPSA56 in the power supply region with a broken leg and the other 2 were touching each other right next to the LM339.
Wondering if some of the other drivers could have been affected by that?
Thats what It acts like is the bias is set to high. The pots are all the way down.
If I install the brown wire positive fuse the amp powers up fine no DC on brown wire.
If I install brown wire negative fuse I have rail on brown wire and pulsing.
If I leave positive brown wire fuse out and install brown wire negative fuse the amp powers fine with no pulsing but I have rail on brown wire.
I didnt find any solder bridges, the outputs are new. The source resistors are new.
Maybe a bad driver or bias transistor?
If I install the brown wire positive fuse the amp powers up fine no DC on brown wire.
If I install brown wire negative fuse I have rail on brown wire and pulsing.
If I leave positive brown wire fuse out and install brown wire negative fuse the amp powers fine with no pulsing but I have rail on brown wire.
I didnt find any solder bridges, the outputs are new. The source resistors are new.
Maybe a bad driver or bias transistor?
Replaced all the A06 and A56 in that channel.
Replaced the 2 outputs in that channel again.
Nothing checks open as far as testing on the board.
Same issue. This is just like the 2 800a2 I could never figure out. Same cinareo, same test to work, same everything.
If I leave the IRF9540 out of the circuit the amp powers up fine. For some reason it does not like that IRF9540 being in there, I just dont get it.
Replaced the 2 outputs in that channel again.
Nothing checks open as far as testing on the board.
Same issue. This is just like the 2 800a2 I could never figure out. Same cinareo, same test to work, same everything.
If I leave the IRF9540 out of the circuit the amp powers up fine. For some reason it does not like that IRF9540 being in there, I just dont get it.
Please read #15 first.
I believe the problem may be with the IRF540 section of that channel.
The gate and source pads for the 9540 with it removed or installed both have rail voltage and none on the drain.
The 540 pads with it removed or installed only have rail on the source pad and not the gate.
Wether I remove the 540 or the 9540 the channel only produces the upper half of the waveform.
I believe the problem may be with the IRF540 section of that channel.
The gate and source pads for the 9540 with it removed or installed both have rail voltage and none on the drain.
The 540 pads with it removed or installed only have rail on the source pad and not the gate.
Wether I remove the 540 or the 9540 the channel only produces the upper half of the waveform.
If it produces clean output up to clipping with a load and doesn't draw excessive current with the jumper in place, that would tend to indicate that ALL of the components in the channel were OK with the exception of the ones for the bias circuit. Carefully check all of the components in the red rectangle for the defective channel.
Attachments
Everything in the bias circuit was completely fine in and out of circuit. All tested within tolerance.
But..........after careful review of the board under magnification I found 2 things wrong.
R122 10k.......Someone had a 1k resistor in its place.
D102 1N5226B was leaky.
I replaced the 5226 with a 4728 same voltage just a 1/2 watt higher its the closest I had on hand. Do you think it will be a problem?
After replacing R122 with a new 10k resistor and D102 the amp powers up and is stable with no pulsing and produces clean audio into clipping.
But..........after careful review of the board under magnification I found 2 things wrong.
R122 10k.......Someone had a 1k resistor in its place.
D102 1N5226B was leaky.
I replaced the 5226 with a 4728 same voltage just a 1/2 watt higher its the closest I had on hand. Do you think it will be a problem?
After replacing R122 with a new 10k resistor and D102 the amp powers up and is stable with no pulsing and produces clean audio into clipping.
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