Stan,
It is getting late on Friday, and I would bet that Elecraft is flooded
with calls. Perhaps I can help.
Was that measurement on the "PA transistor" in the KPA100 or the base K2
(collector of Q7 or Q8)?
Regardless of the answer to that, physically remove the KPA100 and power
the base K2 from the 2.1mm coaxial jack - connect a dummy load to the
ANT jack on the lower rear panel.
Does the base K2 have power output? My guess is that it does not. With
Q7 and/or Q8 shorted, you will get the same shutdown situation.
If so, order the K2PAKIT from Elecraft and replace Q11 and Q13 first,
then with Q7 and Q8 removed, do a TUNE and check the voltage on the
solder pads for the base of Q7 and Q8 - if it is 0.60 to 0.64 volts, all
is well, proceed to install Q7 and Q8. Then again test the base K2 for
proper power output and power control.
Once the base K2 is working, then remove the shield from the KPA100 and
examine it for anything that might look burned, especially the 1k
resistor across RFC3. Check diodes D16 and D17 with your DMM. Also
check diodes D11, D12, D13 and D14 with your DMM. Replace as
necessary. If your KPA100 is not up to date (blue toroids at RFC1 and
L16) this is a good time to update it with KPA100UPKT. If your shield
is not up to date - clips to the K2 side panels, narrow notch at the
SO-239 jack location and solder lugs to connect the outside of the
shield to the SO-239 (and the speaker magnet shield), now is a good time
to do the updated shield as well.
The reason for all those checks is that what normally happens is a
static surge coming in on the antenna feedline will damage D16 and/or
D17 in the KPA100 wattmeter. Once that happens, there will be a loss of
power control, and the power output will always be at max power (which
may be in excess of 180 watts). In time, if that condition is not
noticed and corrected, the PA transistors have been putting out "their
all" trying to provide drive, and will fail. base K2 Q11 and Q13 are
often damaged as a secondary failure.
The other possible failure scenario is that something in the KPA100 T/R
switch failed and caused the other failures. If you have the updated
KPA100, that is a rare occurrence, but if your KPA100 is back-level, it
can happen without warning, particularly while tuning with the KAT100 on
40 meters - a parasitic can develop that can cause damage to the KPA100
T/R switch.
So now you have the full story, and you should be able to determine
which components may have failed.
73,
Don W3FPR
On 8/9/2013 5:42 PM, Stan AE7UT wrote:
I have a K2/100 with a KAT100 that was running into a ZS6BKW.
On 15 meters it was showing "High Current" occasionally. The rig
was turned on one morning and just immediately shut down with a
small amount of smoke coming from the rear of the rig. Now the
rig will turnon, lights up and "Elecraft" show up and then it immediately
shuts down.
I opened the rig and could not see any apparent damage. One of the PAs
has a "short" to ground of about 6 ohms. I'm guessing that PA is dead.
I could be way off on that.
I called Elecraft - left a message - but have not heard back from them.
Any help would be much appreciated.
73
Stan AE7UT
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