On 12/16/2011 5:57 PM, Charles P. Steinmetz wrote:
Larry wrote:
However, while counting the 10 MHz from my HP Z3801A and displaying
0.01 Hz resolution on my 1992, I can rap very smartly indeed with my
knuckles on the outside of the counter case (anywhere) and not change
the displayed count. Further, my counter seem insensitive to
orientation or motion. Of course, I can see only to 0.01 Hz
resolution at 10 MHz.
That has been my experience, as well, with all of the 1992s I've seen,
even using the 10-second gate. I think Chuck must have one with a bad
oscillator.
Ed wrote:
2. Even a completely warmed-up 04E oscillator drifts after the unit
is turned on from standby mode.
Mine do not drift very much when turned "on" from "standby" -- you
have to be in the 10-second gate mode to see it, and even then it is
only a count or two (1 or 2 mHz). The random variation seems to be 1
count or less -- mine often display only 2 or 3 different counts for
months at a time. (Unfortunately, not "000.000000 e3" and "000.000001
e3", because of the lack of a smooth fine adjustment on the oscillator
-- the closest I can usually get when I adjust them is "000.000045 e3"
or so.) The two I own were selected as the best of a lot of 12, but
none of the others was much worse.
My 04E must be less stable than yours. I was monitoring a fully
warmed-up Efratom FRK rubidium and saw a drift of ~ 0.04 Hz (i.e. 40
counts) over two hours after I turned on my 1992 from standby. Are
more than one type of oscillator used for option 04E? Mine is a model 9462.
3. My 1992 doesn't perform properly when the power glitches. Even
on a UPS, the transfer time is long enough that the 1992 resets. The
linear power supply appears to be working correctly and the
capacitors are good, but it just doesn't have enough headroom to
handle the transfer.
All the ones I've played with do this, too. The answer is an "on
line" or "double conversion" UPS. Like ebay item # 190565787556 (no
connection to seller, but I have purchased from him in the past with
good results. Note that he will ship without the old batteries, which
saves significantly on shipping -- you'd want to start with fresh
batteries in any case, which are readily available). With this kind
of UPS, no problem with the 1992s or any other equipment (including
the old Dell that monitors the Thunderbolts and Symmetricom
disciplined oscillators, which always crashed with the slightest power
disturbance). Double conversion UPS's also condition and regulate the
output voltage.
Yes, I'm familiar with the on-line style of UPS. Unfortunately, they're
much more expensive than the regular type. The auction you mentioned
isn't really an option for me. I'm in Canada and the seller has
specified the most ridiculous of UPS's many ridiculous shipping
methods. My shipping costs are shown as $413. Even taking out the
batteries won't reduce that to a reasonable level. Not mentioned is the
UPS brokerage charges and taxes which would add about $50 - $75 above that.
I wondered what the long-term effect would be of changing the line
input setting on the 1992 from the 115V to the 100V position. It would
give better headroom at the expense of more heat. I'd also have to
check for transformer saturation. Another possibility would be to
replace the 04E with any old 10 MHz oscillator and use an external
standard. This would reduce the load on the +5V by a few hundred
milliamps and might make the difference.
4. I have one unit with bad switches and one with good ones. The
body on the good switches is white, the bad ones are black. I don't
know if this is the same on all units or not. You can see the body
if you pull a keycap off. No disassembly required.
IME, white switches are substantially more common -- perhaps 4:1 or
5:1 compared to black switches. I have seen bad switches in units
with both black and white switch bodies with about equal probability,
so I don't think body color is a reliable guide to which are likely to
fail. (I have repaired around 25 1992s, and replaced the guts in over
200 switches. It is the recurve "rubber" spring/washer that fails, by
cracking.) The one thing I have observed is that if one switch fails
in a counter, many more will, too. I have long wondered if it may be
a difference in soldering or board-cleaning at the time of manufacture
that determines which units are problematic and which are not.
Thanks for that info. A sample of only two (one good and one bad)
doesn't give much confidence. How did you replace the switch guts?
Where did you get the parts? I looked at mine and had some success
installing a tiny spring to restore the switch's operation. You lose
the tactile feedback, but at least the switch works. I didn't pursue it
because the other unit is okay (so far!).
I hadn't thought about cleaning causing the switch failure. I just
assumed it was old age with different brands or lots of switches being
made with different recipes for the rubber and therefore different
lifetimes.
Ed
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