[time-nuts] Re: Faulty HP 10544B

[Bruce Griffiths]

N.B. there's at least one error in the circuit schematic for the 10544 at leapsecond.com.
The oven monitor series resistor should be connected to the driven end of the heater winding not to the oven supply via the thermal fuse.

The corrected oven monitor connection is then consistent with the datasheet and the 10544 I used in the early 70's which was easily repaired after its RF output was inadvertently shorted.

Bruce

> On 28/03/2023 14:54 NZDT David G. McGaw via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>  
> 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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