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Hi Nico there are many ways of producing an
external mod source. We all get used to having a standard piece of HP gear for
the job. .......but for instance a comms rx with a xtal calibrator will produce
a tone on the speaker terminals which can be fed to the ext mod socket on the
8640. Ok the impedances may not be optimum, but it is enough to determine if the
int mod source has failed or whether the modulation stages are to blame.
?
Having said that my experience is that a fault like
this (fail after storage) is usually?a psu fault probablt an electrolytic
(or maybe a tant) failing. It may be worth investing in a cheap mechanical time
switch and running the gear up for a couple of hours every day even if not in
use. Smoke detector advisable
?
:-))
?
Alan
G3NYK
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----- Original Message -----
Sent: Tuesday, October 17, 2017 12:23
PM
Subject: [hp_agilent_equipment] HP 8640B
troubleshooting, no AM modulation
Needed my HP 8640B for troubleshooting some radio equipment after 2
years of not using it. Ended up with troubleshooting the?HP 8640B first.
The RF output is not being modulated in
AM (don't know about FM) from the internal source. I have no audio source to
test the external AM modulation input but likely that will not work
either..?
Checked the signal AM output socket and
that is fine on 400 and 1000Hz and the level can be adjusted as expected. The
meter gives normal readings as well .
The RF output has a very faint 1000 Hz
modulation of perhaps a few % dept with the level all the way up and on 400 Hz
no modulation at all . The RF settings and output? are fine.
Any ideas where to look?
Thanks, Nico
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