[Elecraft] K-2 is toasted (I think)

[Ron D'Eau Claire]

I suspect out resident repair guru, Don, W3FPR, is off enjoying turkey or
sleeping off the effects of enjoying turkey. I'm sure he'll turn up soon. 

In the meantime, let me say that smoke can make things easier. Was the unit
open? Any idea at all what part of the radio it came from? Do a very careful
visual search for a blackened part that let out the smoke! 

A magnifier is good for that. See if you can't find the part that went
black. If not, check the trace side of the board(s) carefully for
discoloration anywhere. Traces make great fuses, unfortunately, but,
fortunately, they are usually easy to repair if that happens to you. Rub the
fleshy part of a fingertip over the traces and see if anything flakes off,
indicating a trace that burned and debonded. 

If you can find where the smoke came from, you now know what part of the
circuit has a problem and can start looking for the short itself. 

Check to see what the resistance is between the +12 V connector and ground
with the power switch on. 

The K2 has a self-resetting fuse that should have opened if the current draw
was really excessive. That usually avoids damaging traces unless the short
was before the fuse, but the fuse is right near the power connector. 

If everything looks okay, you can try the resistance checks on page 21 of
your manual to see if you can identify a short. Smoke means that *something*
is damaged and that something may have acted as a fuse to remove the short.
If so, you can then plug in power again and resume the voltage checks in
your manual looking for where voltage are missing to find the problem
circuit. 

Since I brought it up, I've done a lot of service work and here's how I
approach smoked traces. Remove the damaged area so there isn't any loose
conductor flapping around. Use a sharp hobby knife to cut off anything that
still isn't bonded. If it's a small section, you can usually replace it with
a length of solid wire. Use a small diameter. It doesn't need to be anywhere
as wide as the original trace. After all, the trace is very thin; that's
what limits its current-carrying ability. Carefully scrape and tin the trace
on either side of the break, then solder the solid wire across the break. If
the trace bends, bend the wire to stay along the original path and away from
other traces. That's not only to avoid shorts. Traces are sometimes
positioned where they are to avoid coupling to other circuits. 

If you find several inches of a trace damaged, you can replace it with a
length of insulated wire to avoid the possibility of a short, especially if
the burned trace goes around corners, etc. For most work involving low
voltages (< 100 vdc) I strip a bit of wire out of some telephone cable.
Telephone "station wire" will provide solid conductors in your choice of
four colors while the normal handset wire will provide nice, flexible
stranded wires in four colors. 

I know, a repaired trace is the LAST thing you want in your new rig, but
it's far better than NO rig. 

Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Rick
Sent: Thursday, November 23, 2006 2:12 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] K-2 is toasted (I think)


I don't know if I've posted to the right place, but here goes.  Just
finished building my K-2 and when doing the first xmitter alignment I could
only get about 100 milliwatts out.  I checked everything and changed out a
torid which helped alittle to about 200 mw.  Than smoke (from where I don't
know) and no power out.  Also receive volume is low and the s-meter doesn't
seem to work.  With so much wrong where do I start??  Help!  

 

Thank You,

 

Rick, W7AV

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