apmr-1504 audiopipe

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hi all
This amp is not powering up.PS FETs are not being turn on.
KA2535A pin 15 has pulsing .01 to .53v on it.All other pins is below .00v
pin 15 is connected to the emitter of MPSA 651.If i pull the emitter of this transistor from the board i get 11.71v on that leg. Any idea what to check?

1pulsing 5.04
2: 5.39
3: pulsing 11.62
4: .00
5: 4.41
6: pulsing 5.28
7: 12.36
8: 12.71


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The 12v has to be present but also has to have enough current capacity to maintain the 12v. If the voltage is dropping and nothing is getting hot, it's likely that the 12v source has too much resistance. You will have to find the component feeding the 12v to the 3525. When you find it, let us know what it is and we'll help you troubleshoot from there.
If the amplifier is constantly cycling all those lines, it's difficult to determine because the entire unit is trying to turn on, then turns off, turn on then turns off.. hard to see a solid flag in there so Judging by all the posts thus far, and going to the top of the food chain on protection, I'm going to take a blind stab at the PROT line flashing.

Amplifier tries to power up, problem down stream flagged, drags pin 3 down, shuts amp down. As soon as the amp is down, the prot line goes dead and 12v is allowed to flow again. This is where you're seeing your pulse effect and this can happen as rapidly as the parts will skew. You didn't say if you tried to power this up with the FETS in and JUST the rectifiers OUT. Did you do that? Please stop applying power to pin 15 as well, bypassing the protection chain can cause further damage wherever it is.

You MAY not see a power or prot LED without them in, I didn't look. But you can apply power and test voltages where you might expect them. if you get voltages, go back to pin 3 on the 393 and check it again. it should no longer be pulsing. The results would suggest an issue post rectifier flagging the PROT line. Good luck.
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If you can't find the problem, disable the protection circuit by soldering a bridge between pins 1 and 2 of the opto-coupler.

When you power it up, have a current limiter in line with the B+ line and have all transistors clamped tightly to the heatsink.

Does it pull excessive current?

Does it have excessive DC on any speaker output?
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.