[Test-Equipment] Looking for HP quartz oscillator schematic

Sun, 01 Jun 2003 00:21:50 -0400

Carl -

Typically, although not always, there is a thermal fuse in those that once
opened stay opened due to their unique construction. All of my problems with
those oscillators has always been the fuse. That is not to say there are no
other possibilities, HI. They are typically plugged into two small brass
sockets mounted on the PCB. They are slightly larger than a 1/2 watt
resistor and have a metallic cylinder for the case. If the unit has been
left on continuously for years, which they often are, it is no surprise that
the components would appear "baked". Maybe there was a reason for the fuse
to open, like the temperature servo controller quit working and it got too
hot. But, typically, they just open from continuous use. The fuse itself is
composed of two spring loaded contacts that will separate if something did
not force them to stay connected. At manufacture, they are forced to close
and then the cylinder is filled with wax which when it cools keeps the
contacts together. Different mix of waxes are used to open them at different
temperatures. Over the years the wax eventually softens allowing the fuse to
open even if nothing is wrong. See if you can find this device and check it
with an ohm meter. If open, just replace with a piece of bus wire and then
see if the oven starts and also behaves, regulates the temperature. Often
that was my final fix when I did not have other fuses handy. Just left the
bus wire in there and no problems. You may want to monitor the temperature
with a thermocouple if you do get it working to make sure it stabilizes.
Good luck. 73 - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-901-9193

----- Original Message ----- 
From: "Carl Walker" <[email protected]>
To: <[email protected]>
Sent: Saturday, May 31, 2003 5:09 PM
Subject: [Test-Equipment] Looking for HP quartz oscillator schematic

> Greetings, all. I'm looking for schematics or component information on an
HP
> 00195-6013 crystal oscillator. This is one of the dark blue rectangular
units
> that HP used as the reference in many of the early cesium standards, and
> possibly in the 105 series of quartz standards. The unit I have is dated
> 5477, and is Series 1144A.
>
> The one I've got has no oven at present; the "meter" output causes the
oven
> monitor meter to pin at all times, and the oscillator is about 70 Hz high
in
> frequency, and does not change given time to warm up. I pulled the end cap
> off the unit to reveal the PCB - and the 1/2 watt resistor near the 2N1701
> and 2N3053 has definitely seen better days; at some point, all the smoke
has
> escaped from this device. There's also what appears to be a molded choke
to
> the left of the power transistors - at the center and opposite edge of the
> board - that has also run a wee-bit too warm. I can't identify the
intended
> value of either of these components.
>
> If someone has data on this unit, or has one that's out in the open where
the
> end cap can be removed without too much trouble, I'd be much obliged if
you
> could pass along what the values of these devices are supposed to be. If
> you've got a schematic, that would be great - and would probably help in
> bringing this unit back to life (but if worse comes to worse, I can always
> take it apart a little further and trace the circuit out, provided I can
find
> the original values for the smoky components). If a photo of the board
would
> help in pinpointing the components in question, I can take one and send it
> along.
>
> Thanks again,
>
> -Carl, WA1RAJ
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