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HP 8640B troubleshooting, no AM modulation

[email protected] #86275 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 ?
Alan Melia All Messages By This Member #86282 ? 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 ? toggle quoted message Show quoted text ----- Original Message ----- From: nico@... [hp_agilent_equipment] To: hp_agilent_equipment@... 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 ?
Dave Wise All Messages By This Member #86283 开云体育 If you can control the output level with the Vernier knob, that eliminates many suspects, because it uses the same control paths as modulation. ? Dave Wise ? toggle quoted message Show quoted text From: hp_agilent_equipment@... [mailto:hp_agilent_equipment@...] Sent: Tuesday, October 17, 2017 4:24 AM To: hp_agilent_equipment@... 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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