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.
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.
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.
Best regards, Charles _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
