[time-nuts] HP10811 losing EFC

[Pete Rawson]

Rick,

I'm pretty sure there was a 10811A Service Note issued on the fuse  
problem.
IIRC, the early production units used a relatively low temp fuse,  
which proved
painful & was replaced by a higher temp version(maybe twice). I had  
one of
those early units & it failed 2x before I gave up & canned it.

Pete Rawson

On Jan 15, 2010, at 6:47 PM, Rick Karlquist wrote:
>
> 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
>
>
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