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Sunn0))) Beta Lead Head---No Speaker Output
Any Sunn0))) gurus out there? I purchased this last week and I have no output from the power amp, preamp out works fine...I have mulled over this for hours and I cannot pin this down. I checked the test points from schematic and I am getting no voltage on the output coil,should be 60 volts. I tried tracing it back and kept running into bad connection after bad connection and a horrifying solder job by a previous "tech". The output transistors read fine, there were a few smaller transistors on the output board that had bad connections, i re-soldered those hoping that may give me some type of output but nothing. Being I am not that familiar with this amp I was hoping that someone out there could maybe shed some light on this.. There was a resistor that was between the monitor line in and the speaker output jack that was roasted, I can't even tell the value...but even without that resistor there i should be getting output.Any help would be great.Thanks.
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Last edited by wardevans; 09-28-2007, 08:01 AM. -
Start at the power supply. Is there the main powr present there? If not, you won't find it at the power transistors either.Education is what you're left with after you have forgotten what you have learned. -
Go to the link below and download the service manual pages.
http://sunn.ampage.org/site/svcmans/beta/
I think the resistor that burned out was the 10 ohm between chassis ground and the speaker ground.WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
REMEMBER: Everybody knows that smokin' ain't allowed in school !Comment
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You've checked the fuse and socket?
Is the power inlet connected to anything (all 3 wires)?
Does the power switch function (power cord unplugged, ohmmeter)?
Is wall voltage getting TO the PT? Is it the right wall voltage?
Fuses popping? What about with the PT secondary disconnected?
Do you get the 60V with the secondary disconnected (referenced to the CT, not to GND)?
Don't mean to condescend, but it's the 'obvious' that usually screws me up.
Hope this helps!Comment
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He has preamp out, so the mains circuitry must be working.Education is what you're left with after you have forgotten what you have learned.Comment
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All good now..
Swapped out the power board with one I found from another unit. The beta fired right up without hesitation.Thanks for all your help!Comment
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