[time-nuts] HP 103a oven --- opening one up

Randy Leifer redrabbitlosangeles at yahoo.com
Tue Sep 1 00:39:03 UTC 2009

I opened it up, part way. 
I thought I'd post some pics before I dug any further into this sealed oven.
You can see the variable cap (it's casing), but I don't want to "dig" in the wrong place...I fear I may
hit the small circuit, heater resistors, or worse, the crystal.
Please advise.



From: Randy Leifer <redrabbitlosangeles at yahoo.com>
To: time-nuts at febo.com
Sent: Saturday, August 22, 2009 7:24:00 PM
Subject: HP 103a oven --- opening one up

I have an old HP 103AR Crystal Oscillator.
The oven was not warming up.
I replaced 2 tantalum caps, and now it heats/warms up.
The externally geared "fine tune" mechanism works as well, but....
...the "coarse adjust" does not work at all.
The freq is not far off, but is too far for the "fine adjustment" alone.

I believe the "coarse adjust" is a variable cap, inside the oven assembly. 
It is my understanding that this internal var. cap may have a fiber shaft, and it might have busted.
I removed the oven unit (103a-69a), and it's faceplate screws....
....and ,as expected, I am now looking at a sealed tight can, with poured-in-place foam.

I have the means to re-pour/re-seal this if I need to (I work in a mold-making shop).

Any suggestions and/or tips on how to make the coarse adjust work ?
Does it sound like a broken cap shaft ?

(yes, I realize there is a trick to adjusting this cap....push in, until it locks/mates with the shaft, then adjust...but that has no adjustment effect on my unit.)



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