[time-nuts] Re: Faulty HP 10811D

[Adrian Godwin]

I had a 10811 that didn't warm up. I'd never taken one apart before but,
although a bunch of parts had failed, they were all common (if ancient)
op-amps and the like. I didn't have much trouble fixing it once I'd got
started. I'd encourage you to go ahead.

On Tue, Mar 28, 2023 at 7:28 AM Askild via time-nuts <
time-nuts at lists.febo.com> wrote:

> Hi Dennis,
>
> The HP 10811 are serviceable. Just download the service manual and study
> it.
> I would expect the oven to be faulty with this much error.
> Most likely the thermal fuse has gone open circuit.
> The fuse can go open circuit without there actually being any fault with
> the oven, but there might also be a fault in the oven circuit.
> The fuse is on the first PCB you get to after opening up the 10811. All
> described in the manual.
> If its the thermal fuse, replace with correct thermal fuse. When replacing
> make sure to not over heat it while soldering.
> You can of course bridge the fuse with a wire for testing, but then you
> need to monitor it closely, to be sure it does not over heat.
>
> I was lucky to find a HP 8663A in a electronic recycling bin. It was
> missing PCB's in the PSU and the 10811 was totally burnt to a crisp.
> Guess the fuse had been bridged. So I needed to get a replacement off ebay.
>
> Regards,
> Askild
>
>
>
> On Tue, Mar 28, 2023 at 7:49 AM 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 10811D 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 24 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?I have confirmed
> > that the edge connector is supplying 25V on the over supply connections
> > but I don't think the module is warming up.
> >
> > 4) Is it possible  the OCXO has just worn out and has aged beyond the
> > point it can be adjusted back into spec?
> >
> >
> > Regards,
> > Denis
> >
> >
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