I am repairing a HP8560E and until now have
been doing well.
The unit on delivery had the classic distorted
display and no apparent response to any input though it did
sweep it was very slow. 12 Alarms were reported.
Choose the "600 MHz Reference Oscillator
Unlocked" first and replacing failed 2N2222A regulator on the
100MHz oscillator which bought the display back and all the
alarms disappeared. Best 40c I've ever spent.
Was it completely fixed? No unfortunately not,
the input reads about 90dB low. Every thing else looks fine, the
resolution band width, span and frequency accuracy all look
good. Checked the attenuator and the filter and even went
straight into the RF port on the first low band mixer but still
90dB down.
I am at an impass now until I can borrow a
decent SA as I do not have anything to measure 3-6GHz.
I did the LO feed through test in the service
manual ie centre freq 0Hz, Span 1MHz, input attenuator 0dB and
it says the feed through should be between -6 and -30dBm. It
says if it is inside this range the RF path following the Low
band mixer is operating properly.
Mine is -26dBm, so in the range.
My question is does that test mean that the
the Yig, the LO distribution amp, the first mixer LO and IF
ports and all the following mixers are operating correctly
albeit not 90dB out? If so, the only thing I can think is a
faulty RF port on the mixer (sounds unlikely). Also, I suppose
if the LO drive was low, maybe 10 dB or so, there would still be
feed through but may be not enough level to bias the mixer to
mix.
Any though while I wait for a better spec an?
Dave
