Products > Test Equipment

Effratom rubidium strange issue

<< < (2/2)

gossamer:
I was looking at that paper and did some measurements. All seemed ok. Was still locking but freq would drift a bit. Then I disassembled the whole thing and measured those resistors on the lamp board. They were ok.
While whole thing was in bits I said I will turn it on and poke around with oscilloscope, but then the rubidium locked and it was spot on stable. So I assembled the whole thing again and turned it on and it was drifting again. With several screws out of assembly it is locking fine, but as soon as I put everything together its out. Obviously some trace or solder joint is causing the issue. No clue how will I find the cause  :-//
I suppose extra screws in this case might not be that bad ? :)

thinkfat:
I found that spurs from the exciter oscillator can have a quite serious impact on the stability. Try tuning it slightly, see if the problem goes away. Spurs should be visible on the servo test point if you have a scope connected set to slow sweep and untriggered roll.

capt bullshot:
The symptoms look quite similar to mine.
Check the 60MHz level at this end of the coax cable, and the 125Hz output of the servo loop while e.g. fastening the screws / warming up the unit.
If this drifts while handling / warming up, test some small 2pF ... 20pF capacitors near the output transformer. If it is the same as with mine, placing a capacitor here should increase the RF level and the 125Hz signal and keep the unit stable when assembled and warmed up.

edpalmer42:
Check to see if someone mixed up the long and short mounting screws.  Maybe a long screw is shorting something out when you screw it down.  I don't know if there are long and short screws, but Murphy just loves to use tricks like that to drive you crazy!

JoeyDeng:
I meet the same issue with my Efratom FRS. However, the problem wasn't actually caused by the uninstalled capacitor. I spent day and night trying to figure out what was happening with my clock. I attempted to add a capacitor to C30, but it would still lose lock when the frequency generator board warmed up. So, I think a capacitor on the board may be aging. I tried measuring all the capacitors on the board with an LCR meter, but the problem is still not resolved :-//
I lifted the frequency generator board away from the oven to maintain the lock. I'm using a heat source (a wooden stick heated with a 100°C hot air gun) to touch the components on the board. I found that the lock is lost immediately only when I touch Q5. I then thought maybe the Q5 NPN RF transistor is aging. After tearing it down and measuring it, I found that the Rds of Q5 is almost shorted to GND :-DD
I currently don't have the components for replacement, but I will provide updates once they arrive. :popcorn: ;D

Navigation

[0] Message Index

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod