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Old 20th May 2008, 11:42 PM   #11
The one and only
 
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Using a different NPN transistor will not be the problem. If you
inadvertently swapped the wrong pins on it, that could easily
be the problem.
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Old 20th May 2008, 11:49 PM   #12
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Location: Columbia, SC
Quote:
Originally posted by gionag


few seconds after turning on device, the toroid emits a noise like a "fuzz"... as you hear when you pass near an electrical forniture.


The hum from the transformer indicates a very heavy current draw.
You should use a Variac or, failing that, a light bulb in series with the circuit. Check for solder bridges on the circuit board. Don't assume that you've got the transistors installed properly--triple check. Check resistor values. For some reason, I keep seeing threads where people have mounted resistors that have the right significant digits, but are off by 10 or 100 or 1000...that kind of thing will bite you if you aren't careful.
In the final analysis, you're the one with the circuit in your hands. It's your eyes that see the board and parts. Patience and careful problem solving will fix this. Just sit and look at the board for a while.

Grey
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Old 20th May 2008, 11:54 PM   #13
The one and only
 
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Stare at the board....

Stare at the board....

You are getting sleepy....

Sleepy....

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Old 21st May 2008, 12:02 AM   #14
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I don't know about him, but it's working on me...

Grey
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Old 21st May 2008, 05:06 PM   #15
gionag is offline gionag  Italy
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Join Date: Jun 2007
i've checked each components and are ok (at least the 2ohm resistors that i've replaced with new ones).

I also used new 3 IRFP240 paand one new lu1014.

another thing that i noticed:

when i turn on the amp.. on the drain of Q4 i have 50volts after 2-3seconds, but on the drain of Q3 the voltages raise progressivly and i can't reach the 48volt because the 2.2ohm resistors smoke so early.

can help in troubleshooting ?

thanks
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