K2 Problems

[Brent Sutphin WB4X]

I ordered a half dozen of the 1N5711 diodes  and finals for the K2 today.  I
also ordered several of the 2n7000 transistors. I felt like there was some
confusion last night after my original post with the nature of my problem.
After reading my post today it was easy to understand the confusion.

When I turned it on, it came on for a few seconds then a high
current warning and then off.

I meant to say, I turned it on, it came on for a few seconds before a high
current warning and then the radio powered down. If I turn the power off via
the front panel power switch and back on it does the same thing again.  The
K2 finals quickly get very hot as if they are drawing full current, all this
in the RX mode not transmitting . I didn't attempt to transmit.

Hope this helps,
Brent  WB4X

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[Don Wilhelm-4]

Brent,

With that clarification, yes, I can say that the PA transistors in the
base K2 need to be changed.  If you ordered the PA transistors from
other than Elecraft, I suggest that you do not use those transistors -  
Order the K2PAKIT from Elecraft and you will receive a matched pair of
PA transistors plus 2 2N2222A transistors to replace those at Q11 and
Q13.  Do replace the Q11 and Q13 transistors because they often fail
either as the cause of the PA failure (the bias goes high) or they are
damaged as a secondary effect from excessive voltage on the PA
transistor bases.

What is happening is that the current draw is exceeding 5 amps and the
resettable fuse trips turning power off (that is a good thing).

If you have the KPA100, do check D16 and D17 to see if they are
damaged.  If they do not function properly, the K2 will go to maximum
power and that places stress on the base K2 PA transistors. If you do
not have the KPA100, but have either the KAT2 or KAT100, they also have
wattmeter diodes that can be damaged by static.

I would suggest that you install a resistor across all of your feedlines
to discharge static charges that can occur from nearby lightning, wind,
rain or snow.  The common advice is to disconnect the antennas when not
in use, but plugging in PL-259s are especially bad because the center
conductor makes contact before the shell, and if there is a static
charge on the feedline, there is no chance to bleed it off before it
zaps those diodes.  The protection must be in the feedline rather than
in the K2.  I use an antenna switch in the shack and switch the
transmitters to dummy loads when not in use - my resistors are mounted
inside the antenna switch, so I do not have to physically disconnect the
antennas, just turn the switch.

A resistor of 5k to 100k will be effective.

73,
Don W3FPR

On 8/24/2012 4:10 PM, Brent Sutphin wrote:

> I ordered a half dozen of the 1N5711 diodes  and finals for the K2 today.  I
> also ordered several of the 2n7000 transistors. I felt like there was some
> confusion last night after my original post with the nature of my problem.
> After reading my post today it was easy to understand the confusion.
>
> When I turned it on, it came on for a few seconds then a high
> current warning and then off.
>
> I meant to say, I turned it on, it came on for a few seconds before a high
> current warning and then the radio powered down. If I turn the power off via
> the front panel power switch and back on it does the same thing again.  The
> K2 finals quickly get very hot as if they are drawing full current, all this
> in the RX mode not transmitting . I didn't attempt to transmit.
>

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