[Amps] DEAD Alpha 91B

[Michael Tope]

Kimo Chun wrote:

>Mike,
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>Did you get your problem fixed? I am not a subscriber to the list but just happened across the thread...
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>Kimo KH7U
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>I am about to pull my Alpha 91B out of the operating desk to do a post 
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>mortem. The amp has AC power and the 4 fuses on the rear apron appear 
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>good (buzzed them out with my Fluke meter), but nothing happens when I 
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>push the on/off rocker switch (not even a single flash from any of the 
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>LEDs). Any idea where I should look first for a problem.
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>Thanks,
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>Mike W4EF........
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I am embarassed to admit, but I just got after it this evening, Kimo. 
I've had a bunch of other things going on, so I just kept putting it off 
- that is - until my backup amp died last night (looks like something 
arced over on the high voltage rectifier board). I figured that was the 
signal that I needed to start troubleshooting the primary amp :-) :-).  
The problem looks like a 1K ohm x 10 watt resistor R2 on the "MAINS 
BOARD" PCB. It reads on open circuit on my DVM. I think this would  be 
consistent with the observed symptoms. In the troubleshooting section of 
the manual under "91B will not turn on; nothing happens when ON switch 
is pushed", the manual says "Step-start resistor R6 or R7 open". I don't 
see an R7 on the mains board, but this may be a typo. With R2 open, I 
don't see how K1 could energize.

The front-panel rocker switch that some suggested might be the culprit 
checks out okay with the DVM.

73, Mike W4EF