Still chasing SB-101 problems

[Mark Graalman WB8JKR]

  Randall there is no sense in messing with the neutralzation
without knowing that's actually you problem. With the rig in the
CW mode and the carrier level ALL the way down what does the
plate current meter say?

Mark  WB8JKR


On Thu, 27 Mar 2003 22:13:24 -0600 "Randall C. Iliff"
<riliff at COMMSPEED.NET> writes:
> Hello again...
>
> I had been chasing a problem with very low LSB/USB output and
> suspected the
> ALC circuit.  To date I have not found any obvious wiring or
> component
> issues.  After doing some resistance checks, I hooked power back up
> and this
> time heard arcing when MIC control was advanced but couldn't tell
> where
> (obviously I shut down immediately) and repeated visual inspections
> haven't
> turned up any clues.
>
> Since then I have the following symptoms:
>
> 1) Receive side seems to be working fine.
>
> 2) Power output in the TUNE mode looks normal on all bands.
>
> 3) Supply voltages check out almost perfectly
>
> 4) Voltage at the junction of R311 and R312 shows -50 instead of
> called for
> -70 (measured per manual on receive), but R311 and R312 values are
> in
> tolerance.
>
> 5) Voltage at the junction of R308 and R309 shows -77 instead of
> called for
> -50 (measured per manual on receive), but R308 and R309 values are
> likewise
> in tolerance.
>
> 6) PTT switch closure in LSB or USB pegs the plate current meter, no
> RF
> output indication.
>
> There must be some fairly obvious cause for this situation, but so
> far I
> haven't been able to decode all of the clues.  Any SB-101 wizards
> out there
> recognize these symptoms?
>
> (Sounds like a bias problem to me, but given that I'd rather not fry
> the
> finals or the PS, I'm hesitant to retry the LSB/USB power-on checks.
>  I've
> read through the alternate neutralization procedure, and was
> wondering if
> pulling the plate and screen voltage might allow me to do fault
> location
> with less equipment risk?)
>
> 73's
>
> Randy
>
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