[time-nuts] Re: Faulty HP 10544B

[Bruce Griffiths]

Measuring the voltage at the oven monitor pin may be useful in checking if the oven heater voltage is as expected.

Bruce
> On 29/03/2023 01:41 NZDT Bob Camp via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>  
> Hi
> 
> There’s a range of things that *could* be wrong. Some of them 
> are repairable. 
> 
> If you spend some “quality time” shopping, a replacement can be
> had for < $50 delivered. 
> 
> Bob
> 
> > On Mar 26, 2023, at 6:56 PM, Denis Dowling via time-nuts <time-nuts at lists.febo.com> 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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