[time-nuts] Schematic / advice on repair of Datum PRS-50 cesium - ionizer issue?

[Warren Kumari]

Hi there all,

I have 2 Datum PRS-50 "Cesium Beam Primary Reference Source" units.
One of them works perfectly (although, annoyingly the system time/date
cannot be sent to anything later than 2017 because of firmware version :-))

The other, well, not so much - I'd like to get both units working, and then
sell them -- I've also got an FTS 4060, and my wife keep reminding me that
I really don't need 3 cesium devices :-)

The units are managed through TL1 (which I always find unfriendly), but
dumping the alarms gives:
DATUM 08-12-15 14:21:49 M 1 COMPLD "*C,21,08,18,00,00";

This decodes to:
21 - ionizer supply error (>+-0.16 V of memorized nominal value)
08 - oscillator control voltage (>90% <95%)
18 - primary loop gain near limit (1 or 128)


Dumping the variables (RTRV-VARS) gives:
DATUM 08-12-15 14:22:37
M  1 COMPLD
"2,R+Z,11,21,01,08,18,00,+000,+000000,+25.83,01.0,-510,-0011,-068,-0025,-4780,0081,-0039,0131,+0332,5.00,-0006,-4123,+5.08,+24.2,+14.9,-15.1,c,05.2,14.6,0.49,18.6,08.3,002,+279";

Most of these values look within their expected ranges, other than the 5th
to last one (0.49) which is "ionizer supply - voltage (V) across the
ionizer filament", which  should be more like 1.6V, and the 2nd to last
(002) which is "IP HV supply - current (μA) being supplied by the ion pump
high voltage supply (+3500 V)" which the example shows as 025.

I've measured the voltage going to the HV supply, and it aligns with the
numbers the system is reporting (8.4V (3rd to last variable) and 25.7V
(11th variable (+25.83)). I'm not comfortable measuring the output of the
HV supply, but I'm guessing the current it is reporting (002 uA) is not
unreasonable if the ionizer filament isn't getting sufficient voltage.

Is this a known issue? This unit sat (unpowered) in storage for a while,
but I would expect the the voltage over the ionizer filament to be "normal"
if it lost vacuum (unless it completely lost it, and the filament oxidized
and burnt off?!). I've had it sitting and powered for a while and there is
no change on any of the values.

Does anyone have a schematic for the PRS-10, or the Datum 5045A package it
uses? I'd like the try measure the resistance of the ionizer filament /
measure the voltage myself and possibly trace the power section for this...


W

-- 
I don't think the execution is relevant when it was obviously a bad idea in
the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair of
pants.
   ---maf