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8508A (Vector Voltmeter) Problems using the internal calibration routine

Question asked by Uky on Sep 20, 2013
We have an HP 8508A Vector Voltmeter (The modern type with LED displays)
that experiences random phase jumps but only when one channel lags the other.
Shifting the channels makes the error go away.
 
Having performed the internal routines described in the manual section 5 (Adjustments)
I got stuck at "Search and Lock Assy Adjustments" . 5-10. page 5-12.
 
The "UNLOCK" LED never turns on and there is no other indication that I can
find trying to see wether the 1.62 MHz VCO locks. There is an indirect way
to remedy it, and that is to adjust A4R89 so that Error 405 never displays
during startup. I have tried to locate any useable testpoint to actually search
for this 1.62 MHz signal, but I have not been able to find any. The service manual
that came with the instrument has no schematics. There are no further information
to be found at any of the web sites that I have searched.
 
And what puzzles me is that all remaining test setups requires that test # 004
is selected. Hmmm...
 


Ulf Kylenfall  

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