[Test-Equipment] HP 8640B Counter Not Working Properly

[Barry]

Hi Darrell,

Yes, still working on the 8640.  Just started the process of tracing out where/why the counter isn't working when I discovered the ratchet "gear" (in the cam filter housing) is broken and working on repairing that.  Hopefully, once I get that fixed, I won't run into any unobtanium but don't know yet.  I'm encouraged in that most functions on the counter work so if I can get it actually counting, then everything else should be working.

I'd be interesting in anything I can get my hands on.  I have soft copies of the manual but if you have an actual manual, that would be nice.

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "Darrell W4CX" <w4cx at bellsouth.net>
> To: "Discussion of Electronic Test Equipment" <test-equipment at mailman.qth.net>
> Sent: Sunday, March 1, 2015 6:09:07 PM
> Subject: Re: [Test-Equipment] HP 8640B Counter Not Working Properly
> 
> Hi Barry...are you still working on your 8640?  I had one for several years
> and had two problems with the counter, although I never had a symptom of all
> zeros.  Usually there was a decade off, or other weirdness.  I had to find
> some unobtanium 74xx ICs to get it fixed.
> 
> I do have some material (manuals, etc).  Would you like to have them?
> 
> 73, Darrell W4CX
> 
> (HP 1974-2007)
> 
> -----Original Message-----
> From: Test-Equipment [mailto:test-equipment-bounces at mailman.qth.net] On
> Behalf Of Barry
> Sent: Monday, February 09, 2015 12:47 PM
> To: Test Equipment
> Subject: [Test-Equipment] HP 8640B Counter Not Working Properly
> 
> The counter on my generator shows all zeros (both in INTernal mode and
> EXTernal mode when connected via the front panel BNC jack).  I fed the
> external time-base (rear BNC jack) to a counter and verified 5Mhz is present
> there.
> 
> My first step will be to verify that a signal is indeed making it to the
> counter board.  If that is present (and I assume it probably is), then I'll
> have to investigate the counter board(s).
> 
> Is it a valid method to trace out the signal path with a scope?  In other
> words, I think I should be able to verify there are ECL-level and/or
> TTL-level signals along the path and at least be able to see if there's a
> point where the signal stops.  At that point, then I would start looking for
> bad components, etc.
> 
> Is that a viable approach?  I assume that tracing this out with a scope
> probe won't give me false readings due to loading, etc.  Is that correct?
> 
> Thanks,
> Barry - N4BUQ
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