[time-nuts] Questions about HP 5370B
Rex
rexa at sonic.net
Tue Sep 14 19:54:53 UTC 2010
On 9/14/2010 8:28 AM, Dan Rae wrote:
>
> I hate to disagree with John who knows a heck of lot more than I ever
> will, but in this case it will protect the oven from cooking up if the
> control circuit fails with the heater full on, which can happen.
>
> I did have a 5370B with a 10811 that had a bad thermistor in it as
> well as an open fuse. I'd guess that's why -hp- fitted it.
>
> But yes, the thermal fuses can and do fail open for no good reason,
> and it sounds like this has happened here, but I would not recommend
> shorting it out permanently.
>
> Dan
>
>
On the fuse subject, here is a post from Rick Karlquist early this year.
Rick was an HP engineer who was part of the 10811 team.
> -----Original Message-----
> From: Rick Karlquist [mailto:rich... at karlquist.com]
> Sent: Friday, January 15, 2010 8:48 PM
> To:thol... at woh.rr.com <mailto:thol... at woh.rr.com>; Discussion of precise time and frequency
> measurement
> Subject: Re: [time-nuts] HP10811 losing EFC
>
> The fuse in an interesting topic. It is a thermal fuse, not an electrical
> one. It deals with oven failure. It does not prevent the oven from
> failing, but rather limits the amount of damage and smoke if the
> oven runs away. The main purpose is to limit toxic outgassing,
> rather than to protect the oscillator, although it may
> accidentally do that. I have never heard of a case
> of an oven running away, although it is theoretically possible,
> for example, if the thermistor is open or disconnected.
> (I have never heard of a thermistor failing either for that matter.)
> The fuse cannot be soldered in for the obvious reason that it
> cannot tolerate solder temperatures. It is instead inserted into
> a non gold plated socket. In 99+% of "fuse failures", the fuse
> has not blown (as can be confirmed with an ohmmeter) but instead
> is not making contact. You might see if your fuse is still good.
> In any event, I recommend bypassing the fuse with a jumper and
> not worrying about it. There is far more chance of the fuse
> "failing" than the oven running away.
>
> Rick Karlquist N6RK
More information about the time-nuts
mailing list