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Old 11th June 2011, 08:26 PM   #21
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Only half of those are the rail voltage. This amp uses all N-channel outputs so the positive rail is on the center leg of half of the outputs and the negative rail is on the third leg of the other half of the outputs. The output stage seems normal with only 8mv of offset.
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Old 11th June 2011, 08:44 PM   #22
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damn, just started popping fuses - 15, 20, 30 amp fuses. ????/
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Old 11th June 2011, 08:45 PM   #23
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Don't use anything larger than a 10 amp fuse when testing this amp.
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Old 11th June 2011, 08:49 PM   #24
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OK. BUt wouldn't a 10amp fuse blow if the others blew?
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Old 11th June 2011, 08:51 PM   #25
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No blown fuses until i started testing pins 8 & 12 of the LM339D chip. hmmmm???
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Old 11th June 2011, 08:51 PM   #26
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You need to find the fault, not use larger fuses. You likely have a shorted output transistor. After you find the fault and repair it, use a 10 amp fuse.

I'm assuming that you didn't turn the bias pots.
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Old 11th June 2011, 08:52 PM   #27
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The preamp module is the board behind the RCA jacks.
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Old 11th June 2011, 08:55 PM   #28
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nope. they've been the same as when I opened the amp. Each are at about 10 o"clock position clockwise.

On the amp, how do i test which one is bad with a MM?
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Old 11th June 2011, 08:57 PM   #29
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Read the basic amp repair page (link in sig file).
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Old 11th June 2011, 09:02 PM   #30
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Quote:
Originally Posted by Perry Babin View Post
The preamp module is the board behind the RCA jacks.
That preamp board has 2 chips LM833 with 8 pins. i measured both Pins 4 (-13.5V) Pins 8 (14.00V) on both chips before it starting blowing fuses. Darn! gotta find that bad output transistor.
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