[time-nuts] HP 5370B - result
namichie at gmail.com
Wed Sep 15 12:32:17 UTC 2010
The catch with the thermal fuse in an un-plated socket is that as it
ages the socket oxidises and
the heater current generates enough ohmic heating through a high
to heat the fuse through its leads. This opens the fuse the next time
the oven is heated from cold.
I just repaired a 10811 today with the same problem.
Does anyone know the rated temperature for the fuse to drop out?
cheers, Neville Michie
On 15/09/2010, at 8:40 PM, Charles P. Steinmetz wrote:
> After cooling and restarting the 5370B and observing its behavior,
> we judged that it was more likely it had an unheated 10811 than an
> oscillator of lower stability, so we popped the lid (the
> possibility that it didn't have a 10811/10544 was the reason for
> leaving it intact so it could be returned). Sure enough, we found
> a cold 10811 and an open thermal fuse. After replacing the thermal
> fuse with a jumper, all appears normal. (As others have noted, it
> appears to me that if the heater control failed the crystal and
> heater would suffer major trauma before the thermal fuse opened, so
> we deemed it superfluous.)
> Thank you all for your comments and suggestions!
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