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[Amps] Alpha 87A high(er) R-BIAS voltage / Fault 1

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Subject: [Amps] Alpha 87A high(er) R-BIAS voltage / Fault 1
From: "Carcia, Joe, NJ1Q" <>
Date: Fri, 17 Feb 2012 08:42:30 -0500
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Hi all,

My Alpha 87A was experiencing both a Soft/Hard Fault 1.

I replaced diodes D2/D8.  It worked all of two times before it faulted again.

I performed the troubleshooting procedures.  But, sometimes it works great; 
other times I get both a Soft/Hard Fault 1.

Now, regardless of whether or not D2 and D8 are installed, the R-BIAS voltage 
is between 917 to 929 volts keyed.  Specifically, 929 volts with D2/D8 removed; 
917 volts with them installed.  The t/s specs place the voltage at a maximum of 
850.  To me, 917-929v is a bit much.

There were a few instances when I checked out the HV board - removed caps for 
inspection - that the amp wouldn't key afterwards.  But, then it would.  All 
the connectors were properly seated.

So, it appears to be more of an intermittent problem than anything else.

I thought of replacing Q3 and Q4.  

Anyone else experience an intermittent like this?  My next thought is to 
unsolder each resistor and check them.  BTW, the amp has the mods (zener chain, 
spark gap, etc.)

I feel it's something relatively simple.  My thought is that it's a HV board 
problem and not so much with the diodes.  But, before I rip the whole thing 
apart, I felt I'd ask.    



Joe, NJ1Q

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