[Premium-Rx] PLL trouble with WJ-8718 (MFP)

[Gene Anderson]

I'm looking for a bit of help troubleshooting this receiver.  It seems
to have a problem with the PLL for the first local oscillator.  When I
enter a frequency it has to slowly make it's way up or down to the
desired frequency.  I can watch the frequency make it's way up or down
on the signal monitor.  It's as if I were turning the tuning knob
manually.  Also, I notice a certain "glitch" that occurs each time I
cross a 10 kHz threshold in the tuning when I tune manually.  I'm
wondering if the problem is more likely in the PLL circuit (phase
detector, charge pump, lead-lag filter) or in the VCO itself.

Another oddity is that I used to have a different problem.  Before this
tuning issue occurred, I would occasionally get a loud raspy buzz that
was visible also as spikes on the signal monitor.  I could get the sound
to go away by turning the receiver off and then on again, but it would
often come back.  Now that problem is completely gone (without any
intervention by me) and this new problem has taken it's place, as if
they are mutually exclusive.  Not sure if that could provide any further
clues.

I would appreciate any suggestions by the experts out there.  I do have
a background in electronics and repair, though I have been away from
that for a number of years.  My time at Westinghouse probably ended not
long after this receiver was made.  I'm without test equipment beyond a
digital multimeter and an oscilloscope I can occasionally borrow on
weekends. 

Thank you in advance for your attention to this message.  Happy New Year
to all.


Sincerely yours,

Gene Anderson
sidhu at ms12.hinet.net
Taitung, Taiwan