[time-nuts] Re: Efratom M-100 102 not locking

[Magnus Danielson]

Hi,

This is the expected behaviour when the physical package does not 
function, but that can be broken into several different things:

1) The Rb lamp oscillator is not running (fix oscillator, have a 
transistor to replace on one of my 5065As)

2) The Rb lamp darkened (rejuvinating can help)

3) Any of the heating circuits not functioning (probably fairly simple 
problem like opamp or transistor)

4) The RF generation does not work (typically synthesis from 5 MHz to 60 
or 90 MHz and the 5.315... MHz part and those two feed into the SRD with 
some bias voltage)

5) The C-field is lost (rather than just wrong)

6) The detector amp does not function (happend to me with a 5065 having 
no -12 V)

A good start diagnosis is to measure first the lamp voltage, which is 
the detector detecting light at all. If you have that you got a lit RF 
lamp and you got functional detector. With that 1, 2 and 6 is of the 
hook for some time.

The 3, 4 and 5 blocks the synchronous detection, which is the ability to 
detect anything. 5 is bad, but not as critical as 3 and 4.

You can usually sense if the RF lamp oscillator is running, and it is 
fairly easy to detect of the detector does not work. A few check on the 
RF synthesis can reduce likelihood of that being gone.

Hopefully this provide some debugging ideas for you to apply. Please 
keep us updated.

If someone has a schematic or manual, drop the link.

Cheers,
Magnus

On 2025-11-28 02:23, Peter Gottlieb via time-nuts wrote:
> The frequency wanders up and down around the correct 10 MHz but never locks.
>
> The next step seems to pull the tube and let it heat up and see if the Rb changes.
>
> Peter
>
>> On Nov 27, 2025, at 5:10 PM, Wilko Bulte via time-nuts <time-nuts at lists.febo.com> wrote:
>>
>> hello Peter,
>>
>> Obviously it "all depends" on the actual failure.
>>
>> But I did succesfully repair an Efratom FRK-L Rb unit that failed to lock. In my case the temperature of the crystal oven was far too high which in turn made the XO frequency go way out which made it impossible to get an atomic lock. Turned out the oven control opamp along with its drifted feedback resistor caused it. So, cheap fix in the end.
>>
>> I would suggest to measure the frequency it produces first, to get an idea if it is close enough for a Rb lock to be feasible.
>>
>> Wilko
>>
>>> On 27 Nov 2025, at 21:13, Peter Gottlieb via time-nuts <time-nuts at lists.febo.com> wrote:
>>>
>>> I have this Rb oscillator which has output but won't lock.
>>>
>>> Are these repairable?  Worth the effort?  Date code is from 1989 so it may have a lot of hours on it.
>>>
>>> Peter
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