PPI 2150 died.. :(

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Followed the trace from the remote power on. Goes through a diode, then weaves it's way to VR1 (thermal protection?), then to a SIP resistor array that looks to be "pull up"?? Checked with the meter, and there are no breaks between the diode and resistor array. Not clear why this would have a pull up... which is where schematics would be handy! :)
 
Got new transistor only to find it was a solder short on the board.. <embarrassed>


When I apply power now, it is drawing current... I hear a buzz. But the LED does not come on. I only turn the Power Supply on for a few seconds (trying to avoid blowing anything else up), and I have limited the current to 5A.



Is 5A not enough to turn it on? I increased to 10A and the voltage across C35/C36 went from +/- 2.5V to 3V.. but still did not "turn on". Power Supply shows a draw of the full 10A.



Am I being too cautious powering it on? Or is something still broken?


Thanks again for all the advice/help.
 
If it is still pulling 10 amps I would continue your troubleshooting.

As a note, I use a 2A 12v laptop supply with a peddle and pulse the peddle to build rail voltage watching the scope closely. If there are any shorts anywhere in the amp it shuts down my supply. I can power up almost any amp with this method.
 
A 100w 2 ohm resistor (looks like the ones in the photo) on a full current power supply will give the most consistent results and won't shut down which allows low-voltage troubleshooting when an amp is struggling to power up. I have current limited supplies and after trying them over the resistor, I always went back to the resistor. The footswitch works well but I only use it in parallel with the remote switch on my power switching box.

What's getting hot (of the heatsink mounted components) when you try to power up the amp?
 

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Just tried it again, left it on for about 15 seconds.. Feels like Q55 is what is getting hot.

I think this is one of the parts I changed twice already.. It looks to be a different "batch" than the others. The (what I think is) the date code is different on that one.


For some reason, I can't seem to post a photo..
 
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You can remove this transistor for testing. Before you can return the amp to service, you have to change all 5 transistors in the bank with the odd FET. They have to be relatively closely matched. Having them all from the same production batch is close enough. The FETs in a single bank (two banks of 5 in this power supply) must match. The FETs from one bank don't have to match the other bank but you should not reuse FETs that were in the amp when any of the FETs fail.

What is the value of the gate resistors in your amp?

How are you using the term 'rails'? The term is generally used for the power supply voltages (rail voltage).
 
100 OHM resistors.. They were changed when the transistors were changed to Z44N.


Maybe I am using the wrong terms? This is part of the power supply, So one "bank" is for the + side, the other bank is for - side... correct? Either way, you answered my question- I only need to match the transistors in a single bank.


Anyway, would mismatched transistors cause the problem I am not seeing? I don't think it would.. Something else is causing the high current draw I think.
 
Mismatched transistors won't cause excessive current draw. What happens with mismatched transistors is precisely what you saw, one transistor working harder than others. The amp will be most reliable when all parallel parts are sharing the load equally.

The two banks of PS FETs work in a push-pull configuration. The output of the transformer swings positive and negative due to the drive of the PS FETs and that output is rectified into positive and negative rail voltage.

Are you 100% sure that the gate resistors are 100 ohms?

Have you measured the resistance across the terminals of the PS FETs to make sure that nothing was damaged when the odd FET failed.

Let it try to power up for a bit longer to see if anything else heats up.
 
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