[Test-Equipment] Blank Spots In HP8640B Tuning??

[Hsu, Aaron (NBC Universal)]

You might have the common problem with the 8640b range switch contacts - they become loose.  

EB5AGV has a good write-up on how he repaired his two 8640b's.  Links are here:

  http://www.jvgavila.com/wb1.htm
  http://www.jvgavila.com/hp8640b.htm

And, for completeness, homepage here:

  http://www.jvgavila.com/


Now that I think about it, I should take apart my 8640b and check the switches...


73 & GL,

  - Aaron Hsu, NN6O (ex-KD6DAE)
    {nn6o}@arrl.net
    {aaron.hsu}@nbcuni.com
    No-QRO Int'l #1,000,006
    . -..- - .-. .-   ".... . .- ...- -.--"

 

-----Original Message-----
From: test-equipment-bounces at mailman.qth.net [mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Steve Harrison
Sent: Tuesday, November 28, 2006 9:59 PM
To: test-equipment at mailman.qth.net
Subject: [Test-Equipment] Blank Spots In HP8640B Tuning??

Just dragged out my old 8640B which has been stored for around 7 years.
After some clean-up, it's working as well as I rember except there are two blank spots in the tuning range as if the tunable oscillator stops oscillating. Output drops to zero. It runs at the lower end of the range then quits about 30% the way up, starts up again maybe at 35% through maybe 40% then quits again all the way up to the highest end of the range. The multipliers or dividers (I forget which these things have) are working fine. It locks up nicely although just as I rember from years ago, there's a small amount of cyclic FM modulation, sounds like maybe 50 to 100 Hz and I believe it's synchronized with the display counter's updating. Not too concerned about that right now, but the blank spots happen to cover the HF ham bands  8-((((((((((((((((((((

What to look for?? I no longer have a manual and haven't been able to download the one on Bama.

The fan was also not running but I finally got it going after dripping a cupla drops of Liquid Wrench's Super-Lubricant into the front and rear bearing locations. Will have to keep an eye on it, though, in case it quits again. Anyone know whether the fan driver circuit will survive if I simply unplug the fan and install a small muffin fan on the outside?? The alternative is to find another fan from a junked unit......  Looks like it's a four-phase thingy made by Siemens.

Thanks,
Steve K0XP