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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