[time-nuts] Re: Faulty HP 10544B

[David G. McGaw]

It does sound like the oven on the 10544 has failed.  There is a lot of 
info on the unit at http://leapsecond.com/museum/10544/.

Also, if you choose not to or cannot repair it, any commonly available 
version 10811 oscillator is plug-and-play (only the 10811B is not).  It 
will replace a 10544 with no re-wiring.

David N1HAC

On 3/26/23 6:56 PM, Denis Dowling via time-nuts wrote:
> Hi All,
>
> This is my first time on the list so apologies if I am going over an 
> old topic.
>
> I am repairing a HP 8662A Synthesised Signal Generator that I 
> purchased from a government auction. The unit was purchased without 
> any information about its working state and I have fixing various 
> issues with it. Firstly there was a digital logic problem with the 
> keyboard card that was causing the generator to periodically lock up. 
> When this was fixed the unit came to life but the output signal level 
> was down 5dB and this was traced to a bad step attenuator. I attempted 
> a fix but ended up needing to replace this to get the output steps 
> correct.
>
> I have now turned my attention to calibrating the reference timebase 
> and unfortunately this seems to be well out of spec.
>
> The timebase is a HP 10544B 10MHz OCXO. The 10MHz output of the 
> oscillator seems to be ~40Hz low. I have attempted to adjust the unit 
> via the multi-turn capacitor adjustment but this seems to be at the 
> end stop and the frequency is still low. So my questions are:
>
> 1) I assume this module is faulty as it is so far out of spec? The 
> signal generator has been powered off for multiple months but even 
> after having the unit powered on for 6 hours the frequency has not 
> changed significantly.
>
> 2) How repairable are these modules? I ended up blowing $200 on the 
> replacement step attenuator so will need to save up for any new parts. 
> I can always use an external 10MHz reference but it is always nice to 
> have equipment complete.
>
> 3) From searching the list it seems that the oven could be what is 
> faulty. Would a cold over account for this much error? If so I will 
> pull the module and check this.
>
> 4) Finally is the OCXO just worn out and has aged beyond the point it 
> can be adjusted back into spec?
>
>
> Regards,
>
> Denis
>
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