HP 5071A Cesium Beam Error - Need Info & Schematics

Started by Hawaii596, 11-04-2016 -- 10:19:40

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Hawaii596

11-04-2016 -- 10:19:40
Our HP 5071A Cesium Beam has the following error:

"CBT Oven Supply Regulation Failure" and the green CONTINUOUS OPERATION light is extinguished.  Trying to determine if this a repairable issue (as opposed to needing a new Cesium Beam Tube).

Is this maybe a power supply voltage out of spec?  Or is it the start of a bad Cesium Beam Tube?

And, does anyone have schematics for the 5071A?  I think it is now owned by Micro-Semi (?).  This is an important house standard.  I am sincerely hoping it is not a bad tube.  Or at least perhaps something where we can get the tube repaired, or hopefully repair something else in the unit - anything but a new Cesium Beam Tube.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

briansalomon

#1
11-07-2016 -- 12:19:56
I do not have the service manual for the 5071A. My service manual for the 5061A does show the module Cesium Oven Controller Assembly A11 circuits "provide power to the Cesium tube as required. In addition they supply power to the hot wire Ionizer, mass spectrometer (in-beam tube), 16 Volts and 300 Volts to operational amplifier A9, minus 10 volts to AC amplifier assembly A7 and voltage for the front panel Circuit Check meter indication when set to CS Oven".

Sounds repairable if you can find the schematics.
Bring technical excellence with you when you walk in the door every day.

Hawaii596

#2
11-07-2016 -- 12:33:27
I think so.  Just now talking with the tech working on it. The 5071A appears to be quite a bit different inside compared to the 5061B or C (we have one each of those two as well - with possibly depleted tubes).  I tried running a mainentance procedure to bring one of them back on line, but to no avail.  5071A has been working well, though. One encouragnig possibility is that its output frequency appears to be correct and stable (we have an engineer who is developing GPS timing hardware (not in cal lab) who said that.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

briansalomon

#3
11-07-2016 -- 12:57:04
I just spoke Corby Dawson, with the guy we have used for years for tube replacement and he says he's never seen any schematics for the 5071A.

He's no longer in business and may be a source for spare parts. He's looking to see what spares he has for that model.
Bring technical excellence with you when you walk in the door every day.

Hawaii596

#4
11-07-2016 -- 13:25:12
I will remember that.  The tech working on it has a bunch of other things going on. But if we get to a point of needing to replace a board, I will try to remember, and bring it up here.  If it is a simple thing like a capacitor, etc., we will probably buy off the shelf items as needed.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

Hawaii596

#5
11-07-2016 -- 14:32:35
Tech is working on the 5071A and doing the paint by number troubleshooting to begin with.  One of the first fails is the resistance of the thermistor that is inside the CBT (Cesium Beam Tube).  They expect 200 to 250 kOhms.  He got 6.35 kOhms. Troubling.  The instructions said to check readings, then replace the CBT.  Not what I want to hear.  So, he is looking into if this may possibly be locally repairable.  alternatively, looking into if anyone can do CBT repairs and repair the bad thermistor. Still doing the troubleshooting. More later.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

Calwiz

#6
11-15-2016 -- 07:37:53
We decided that the resistance specification was misleading and the 6.5 ohms is reasonable. Additional trouble shooting points to the A7 board (simulating 20 degrees Celsius with a 10K ohm resistor on the A2's extender board fails).  Oh well .
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