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

[wkb at xs4all.nl]

Hi Mark,

 

Have you checked if the xtal heater is working correctly / stable and is not dropping out? If the Xtal oven temperature goes haywire the frequency of the oscillator goes off far enough that Rb lock fails.

Which is no surprise of course.

 

Today I managed to fix my FRK-L (EUR 15 hamfest grab) which had no less than 3 problems:

1 - the current limiting transistor of the xtal heater was a dead short resulting in a cold oven. Easy find.

2 - the carbon-composite feedback resistor R7 had drifted from 2 Mohm to 3.6 Mohm

 

Once 1 &2 were fixed I found myself with an oven temperature going past +100 Celsius (au!). There is no thermal fuse (not good).

Failure 3 proved to be  opamp U1. Once replaced, the oven temp became stable at 76 Celsius, this temperature is handwritten on the oven assy.

 

I now have stable Rb lock.

 

Hth, Wilko

 



-----Original Message-----
From: paul swed via time-nuts <time-nuts at lists.febo.com> 
Sent: 12 October, 2023 14:42
To: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
Cc: Mark Hughes <gm4ism at yahoo.co.uk>; paul swed <paulswedb at gmail.com>
Subject: [time-nuts] Re: Racal Dana 9457 Rubidium with intermittent lock

 

I looked up that reference online and there is a blog on eevblog about it.

There is a front panel meter. Since the unit locks for a bit what is the meter showing?

On efc, slowly drifting up or down.

Lamp voltage gives good hint to the lamp output. Is it stable or maybe slowly dropping off.

Also the lamp could be dropping out and coming back on. They do that near the EOL.

Best of luck. Looks like a nice unit.

Paul

WB8TSL

 

On Thu, Oct 12, 2023 at 1:34 AM Mark Hughes via time-nuts <  <mailto:time-nuts at lists.febo.com> time-nuts at lists.febo.com> wrote:

 

> Hi

> 

>   I have just started refurbishing an old 9475

> 

> It did not work at all to start.

> 

>    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.

> 

>   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

> 

>   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 9475  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.

> 

>   Thanks in advance

> 

> Mark GM4ISM

> _______________________________________________

> time-nuts mailing list --  <mailto:time-nuts at lists.febo.com> time-nuts at lists.febo.com To unsubscribe send 

> an email to  <mailto:time-nuts-leave at lists.febo.com> time-nuts-leave at lists.febo.com

_______________________________________________

time-nuts mailing list --  <mailto:time-nuts at lists.febo.com> time-nuts at lists.febo.com To unsubscribe send an email to  <mailto:time-nuts-leave at lists.febo.com> time-nuts-leave at lists.febo.com

-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 19415 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20231012/6106bc59/attachment.png>