Why is 40 volts DC comming out of my amps left channel? - diyAudio
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Old 13th March 2006, 07:51 PM   #1
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Default Why is 40 volts DC comming out of my amps left channel?

This problem started seeking a solution a week ago with the name of "testing FET transistors"

My hunch of a muffled buzzing and crackling sound comming from the left channel of my 88 princeton chorus turned from a blown transistor problem to wide spectrum of causes including dirty pot connections, leaky capacitors, fried resistors, and transformer problems. I have now found that 40-50 volts is being sent from the left output.

Are there any normal causes for this?
How can i fix them if so?
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Old 13th March 2006, 08:11 PM   #2
Netlist is offline Netlist  Belgium
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If the amp is so damaged as you describe, I'm not surprised it has that much DC on the output.
Start with finding a schematic if you don't have it, measure every semiconductor and resistor. Recap thoroughly. Try to decouple the output stage and use a variac.
Good luck. Can you share a picture?

/Hugo
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Old 14th March 2006, 01:40 AM   #3
anatech is offline anatech  Canada
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Hugo,
The transistor in question turned out to be an IC amp chip.

sound_prodigy,
If things were that easy we wouldn't need trained technicians and test equipment. Like a detective, you need to find out some facts and follow clues to the answer.

Get the schematic and make some measurements. I did link to the IC data sheet, so start by measuring all the voltages with respect to ground and posting.

-Chris
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Old 14th March 2006, 05:38 PM   #4
Netlist is offline Netlist  Belgium
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Well this thread should go to chip amps then?
I should have asked for a schematic.

/Hugo
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Old 14th March 2006, 05:44 PM   #5
anatech is offline anatech  Canada
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Hi Hugo,
I think we should have continued the same thread as before to provide continuity. Waiting input from sound_prodigy. I want to be certain it's the same amp.

-Chris
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