[Elecraft] Dead K3

[Mike Morrow]

> I was able to do some diagnostic work to determine that D35 is shorted. How
> this could happen is a complete mystery?  I've never had anything plugged
> into J11 (the 12V accessory out jack), so don't quite understand this.

That is odd.  About the only thing one would expect to cause that is an
external power source of reverse polarity connected to J11...but then one
would expect F2 to blow before D35 was destroyed.  Strange, especially when
nothing at all has been connected to J11.

But, how are you sure, short of disconnecting one end of D35 and measuring
resistance forward and reverse, that it *is* D35?  Shorts anywhere downstream
of D34 would show identical results.  C272 could be shorted...a trace in
the path could be shorted...C220 or J11 could be shorted (but then F2 should
blow).

> The trace from the end of D34 to RF choke RFC48 is a little over-heated but
> still usable (well, I never had plans to use external power for anything so
> it won't be a problem).  I'll discuss this with tech support in the AM and
> this may be as easy as lifting D35 and it's good to go.  Maybe...

Were it mine, there's no doubt what I'd do immediately...cut one lead of D35
and verify that the short is cleared on both sides of D34.  If no fault is
detected, apply DC power and see if the radio will power up properly.  That
would show no damage has been caused to Q2.

If there is still a ground fault shown, I'd cut D34 to isolate all of the path
to J11.  It could be that D35 isn't the problem after all.

In any event, the solution should be trivial and quick since you don't need
to supply anything from J11.  Worst case, cut D34 (not D35) to isolate all
possible faults and troubleshoot the short, some time later.

Mike / KK5F