[time-nuts] Questions about HP 5370B

[Bob Camp]

Hi

A little guess work:

Over a 10 year period something like one in 1,000 to 1 in 10,000 10811's fail. Of those, less than 1 in 1,000 are controller run away. Of the controller run away's 1 in 10 might be stopped by the thermal fuse. That puts you at a 1 in 1,000,000 to 1 in 10,000,000 chance of the fuse doing you any good. The 10811 sells for $125 any day of the week on the e place. 

If you are paying more than a tenth of a cent for the thermal fuse, it's wasted money.

I doubt any of my ratios are on the low side....

Bob



On Sep 14, 2010, at 7:15 PM, "J. L. Trantham, M. D." <jltran at att.net> wrote:

> There is a good trouble-shooting tree in the 10811 manual that addresses
> these issues.
> 
> I had a 10811 where the oven would not come on.  I found the thermal fuse
> open and even ordered the replacement part from HP.  It was only a couple
> bucks IIRC.  I also found some close ones for only a few pennies.
> 
> Once replaced, I went through the trouble-shooting tree only to discover all
> things working correctly.  It has done fine since with no further fuse
> failures.
> 
> Joe
> 
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Dan Rae
> Sent: Tuesday, September 14, 2010 10:28 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Questions about HP 5370B
> 
>  On 9/14/2010 1:23 AM, John Miles wrote:
>> 
>>> As Bruce suggests, you'll want to peek inside to see that you
>>> really do have
>>> a 10811 oscillator. If so, then it sounds like the thermal fuse
>>> (F1, inside
>>> the 10811) might be open.
>> Just short it out, or if you like, put in an NTE part with a similar temp
>> rating.  It serves little or no useful purpose.
>> 
>> -- john, KE5FX
>> 
>> 
>> 
> 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
> 
> 
> 
> 
> 
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