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

[paul swed]

Julien
Sorry to here.
Yes that 3V reading is telling you there is most likely no light.
The rb requires 2 things to effectively work to illuminate the photocell.
Lamp ignition and the correct lamp temp.
On less expensive units its possible to see if the lamp is lit as the
assembly pulls out and the rf assembly is still attached. Do not know if
you can do that on the FRK.
I would see if the lamp ignites and they do run hot.
Good luck.
Paul
WB8TSL

On Tue, Feb 1, 2022 at 5:25 AM Julien Goodwin <time-nuts at studio442.com.au>
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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