[time-nuts] Re: Efratom FRK with "inoperative lamp"

[Matthias Welwarsky]

A couple of things to check:

The FRK has a separate power supply pin for the heating elements. Be sure to 
connect it.

If the lamp still doesn't light up, check the temperature of the lamp housing. 
I'm afraid this won't be easy without disassembling the unit.

If the temperatures are correct, see if the exciter oscillator is working.

The lamp itself is unlikely to fail unless it's physically cracked.

Good luck.


On Dienstag, 1. Februar 2022 10:17:59 CET Julien Goodwin wrote:
> I picked up an Efratom FRT a while ago, and it finally arrived the other
> day, sadly it doesn't lock.
> 
> The oscillator inside is an older Efratom FRK, and it's also clear
> someone had been inside already, although it does appear to be complete.
> 
> The FRK manual does include a key description I wish I'd noticed a few
> days ago before full disassembly:
> 
> "Terminal pin 7 provides an indication of proper operation of the
> rubidium lamp. For nominal operation the signal is 6 to 12V. An
> inoperative lamp is indicated by an signal of approximately 3V. The
> internal resistance of this circuit is approximately 6K."
> 
> ... indeed I'm seeing 3v on that pin.
> 
> Based on the circuit this appears to simply be the output of the first
> stage op-amp from the photo-cell, so is this effectively an indication
> that the (electrical part of the) lamp is dead? Certainly it wasn't
> anywhere near the temperature it should have been when I removed the
> bulb after running for over an hour.
> 
> Just for completeness, the unit does draw up to ~0.8A when started up
> cold with 24V, dropping down to about ~0.5A after a while. The sealed
> sub-section of board A4 seems be where all the heat is, and I'm assuming
> that's an ovenised part of the crystal oscillator.
> 
> I also popped the rubidium bulb out and confirmed there's no obvious
> issues there.
> 
> I do have another FRK here, but as it's an FRK-LN, and it's also my
> working house standard I'm somewhat loath to open it up lest I end up
> with two dead units and zero working.
> 
> Any suggestions?
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