[time-nuts] Racal Dana 9457 Rubidium with intermittent lock

[Mark Hughes]

Hi

 Â I have just started refurbishing an old 9475

It did not work at all to start.

 Â  I have replaced all the 10 uF 35V caps in the Efratom FRK unit (one 
was dead short) and now it  powers up, achieves lock in about 7 min and 
works fine for about 1/2 hour.

Then the lock light starts to flicker, within an hour it is more off 
than on.

 Â When it is on, the lock seems genuine, I see the 10 MHz jump ( I have 
it on a scope  with the other timebase from a GPSDO at 10 MHz) and it is 
stable WRT that.   When showing unlocked, the 9475 10MHz off freq by 
about 0.05 Hz

 Â Has anyone seen this behaviour before? I cant see any more 
electrolytics / tants to change in the FRK .  This sort of behaviour is 
typical  of failing electrolytics.

The actual 9475Â  is good, it works with a different Efratom module with 
all voltages nominal and stable.

The boards in the Efratom FRK don't quite match up with the schematic I 
have downloaded,  it's similar but not identical.

 Â Thanks in advance

Mark GM4ISM