[time-nuts] Re: Turning off display on HP 58503 A or B

[ghf at hoffmann-hochfrequenz.de]

Am 2022-06-02 19:55, schrieb K5jv via time-nuts:

> On a different subject:Â  A couple of month back I got some strong
> criticism about suggesting that the oven in the Z3801A was a potential
> source of problems.   I just got another Z3801A in for repair.  Same
> symptoms as before;Â  appears to turn on normally but after a while
> goes into holdover and stay there,  same LH flat lines.  Once again
> the problem turned out to be the oven.  It was unusually hot to the
> touch.  Changing the oven solved the problem.  Now my question.  I
> have never opened one of these oven, so have no real idea exactly what
> is inside.  I would  suspect that one of  the oven's thermostats is
> stuck in the "on" position.  Since it is a "double oven",  there could
> be two thermostats?   If these are mechanical contacts, as one might
> expect fro the 1995 era, can they be cleaned or replaced?   Comments
1965 ???
> from anyone who has actually seen inside one of these ovens would be
> appreciated.

I had a Morion MV-89A that stopped oscillating when the tune voltage
was > 0.8V. I opened it and recovered the SC 5 MHz crystal. It had
parameters that could be expected from such a crystal, quite good.
The xtal parameters were not too different between room temperature
and 85°C, stability obviously excluded. It is possible to do most
development work for a new oscillator without burning one's fingers
too often.

There is one thermistor in the inner oven; in the outer oven
there is probably sth. else, but nothing mechanical.

<   
https://www.flickr.com/photos/137684711@N07/49585174873/in/album-72157662535945536/ 
    >

and from there to the right.