[time-nuts] Re: Faulty HP 10811D

[Askild]

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
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com