Why is 40 volts DC comming out of my amps left channel?

sound_prodigy · 13th March 2006, 07:51 PM

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?

Netlist · 13th March 2006, 08:11 PM

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

anatech · 14th March 2006, 01:40 AM

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

Netlist · 14th March 2006, 05:38 PM

Well this thread should go to chip amps then?
I should have asked for a schematic.

/Hugo

anatech · 14th March 2006, 05:44 PM

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

13th March 2006, 07:51 PM	#1
sound_prodigy diyAudio Member Join Date: Oct 2005	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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13th March 2006, 08:11 PM	#2
Netlist diyAudio Moderator Join Date: Jan 2003	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

14th March 2006, 01:40 AM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

14th March 2006, 05:38 PM	#4
Netlist diyAudio Moderator Join Date: Jan 2003	Well this thread should go to chip amps then? I should have asked for a schematic. /Hugo

14th March 2006, 05:44 PM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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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