Hi Just as a guess, it would be rare for a “heated wire” type of thing to have much over a 10:1 ratio between hot and cold. Most have ratios that are less. (think of a light bulb …) If you suspect the ionizer, I’d suggest working out just what it’s resistance is. If it’s down below 0.1 ohms (and your 1V / 1A guess is correct) then it is shorted. Is it worth trying something crazy to unshift it? Who knows …..
Bob > On Nov 1, 2018, at 3:56 PM, Dirk Niggemann <dirk.niggem...@gmail.com> wrote: > > Hi, > > I acquired a PRS-50 Caesium beam frequency standard in more-or-less working > order back in 2011. The manufacture date was February 2001, so the tube was > probably exhausted by this stage, but it did still achieve lock so may have > been in storage for some time rather than run for the whole of its 10-year > lifespan. > > I recovered it from storage a year or so ago to test and it worked, > initially. The power supply was noisy, and the system wouldn't achieve lock > on power-up from cold. > > I suspect that that it may have been retired from service originally for > an intermittent PSU failure as it would not find lock on every power up, > rather than an exhausted or failed tube. > > Since then the power supply in the 4201A module failed completely. All the > electrolytics in the SMPSU leaked. > > I have managed to restore the PSU to the point that the PRS-50 boots and > tries to find a lock, but fails after about 15 minutes with error F3 > (ioniser voltage out of spec) > > When watching in monitor3, I can see the both the OCXO and the Caesium oven > power and heat up, and i have voltages in spec on all rails, except that > the ioniser voltage remains below 0.1V. > > I also see almost no ion pump current. which is consistent with the ioniser > remaining off. > > I haven't managed to retrieve the tube constants, but i assume the ioniser > wants about 1V at 1A like most other Caesium beam tubes. > > I believe i have also identified the ioniser supply leads from the tube and > these meter out at very low resistance (< 1 ohm), possibly too low (though > how a hot-wire ioniser should fail short escapes me). > > Does anybody know how the 4201A module generates the ioniser voltage? It's > likely to be similar to the FTS4065C in that respect. When is the ioniser > meant to turn on in the power-up cycle? > > I suspect i'm missing the ioniser supply rail. There's at least 24 > unlabelled connections between the SMPSU board and the junction board which > connects both the LV lines for the Cs tube, the main processor board and > the SMPSU. I have no idea which particular connection this could be. > > I don't believe Datum/Symmetricom/Microsemi ever published schematics for > this Caesium module so I'm a little at a loss where to go next with > troubleshooting. > > I'd like to at least eliminate a failed tube as far as possible, since i > really don't see myself acquiring a replacement tube at list price. > > Unfortunately i don't have any test equipment that will work at the > microwave frequencies needed to do a direct test of the tube. > > Suggestions? Has anybody ever tried a repair like this before? I'm tempted > to feed an external supply to the ioniser to see what happens, or at least > disconnect the ioniser leads to see if it fails with an ioniser overvoltage > instead. > > Regards, > > Dirk M0KRD > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.