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Old 22nd September 2009, 08:27 PM   #11
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My Vgs is high then, surprising the fet has held up.

I sent you a pm.
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Old 22nd September 2009, 08:31 PM   #12
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The Vgs probably isn't high. When the gate is 10v above the rail, the source is at the rail so the Vgs is only 10v.


I sent the service manual.
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Old 22nd September 2009, 08:49 PM   #13
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Thanks, got it. This should help.
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Old 22nd September 2009, 10:06 PM   #14
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So I have what seems to be nice square wave osc. on the source of FET101 and the drain of FET191. Measure about 80Vpk-pk roughly 64Khz.

I get very little amplitude when running a 1Khz sine into the inputs. I can vary the amplitude without any change in the output. Should I be looking at the LM339?
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Old 22nd September 2009, 11:06 PM   #15
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Not much of the 1k sine wave is going to make it through the crossover. Go to a 60hz sine wave.
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Old 22nd September 2009, 11:57 PM   #16
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Default Good point on the 1KHz not making it through the cross over.

The guy that suggested a 1KHz test signal probably forgot this is a sub
amp!
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Old 23rd September 2009, 01:50 AM   #17
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That is funny, never even thought about it being a sub amp!
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Old 23rd September 2009, 12:48 PM   #18
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Thanks Perry for the help, the amp is functioning. I only have one set of output fets in place right now but that is enough to hear some sound from it.

Amazing what happens when the correct freq gets through!!

So to sum up the issue: Bought from ebay known bad, output caps burst, one fet shorted and the NE5532 that gets feedback or feeds signal to output was damaged. It also had a couple SM resistors burned in that circuit.

That is 3 amps repaired this week, 1 punch 60DSM, 1 Pioneer GM-X502, 1 MTX 421D.

Thanks,
Cory
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Old 27th September 2009, 07:57 PM   #19
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Dear Brandes.cm:

I suggest to you acquire the Perrys tutorial repair amp.

“The information provided in this tutorial will help you to avoid making the most common mistakes and will greatly increase your chances of success”

http://www.bcae1.com/repairtutorialcdinfo.htm
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