Old Alpine 3525 does not start

Mjimenez

Member
2017-12-20 3:08 am
Hello friends, here again bothering you I find myself trying to repair this amplifier of the alpine brand and model 3525, the problem is that it turns on, but the pwm pulses for the PS transistors do not leave. I checking the upc494 and the protection pins, but I found the one of Dead time (pin 4) meets 4.9v ... Try to track where they came from but I got lost and I didn't know where they originated if someone knew about the diagram or will guide me for repair I would appreciate it greetings
 
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Mjimenez

Member
2017-12-20 3:08 am
here it is, and the upc1270h (Rh channel) that is inside the red circle gets quite hot, i take a read of all its pins and on pin 5 it reaches 12v and the channel LH ​​-4.7v the latter does not overheat
 

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Pin 5 is feedback so if anything in the feedback loop has failed or is out of the circuit, that pin could be well off of what the working channel reads.

Is that with the outputs out of the circuit?

The emitter resistors in these amps often develop bad connections.

There may not be a reliable source for these ICs, if one is defective.

If you cannot find a bad connection or component in that channel, swap the ICs to see if the problem follows the IC.
 

Mjimenez

Member
2017-12-20 3:08 am
I already changed them, and the heating persists and the 12v on pin 5, cold welds were checked and the transistors like PS and output are fine for now I will continue investigating where those 12v come from I am being guided by the schematic of the 3566 that you provide in the tutorial to see that I find greetings
 

Mjimenez

Member
2017-12-20 3:08 am
I have managed to lower that voltage and get the right channel to work but the left channel continues to heat up, a small welding pearl formed a bridge on the switches and came out of protection, now we just need to check the operation of the left side insert the ic to see if the first one was damaged
 

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