[Elecraft] Ailing K2

[Don Wilhelm]

Tommy,

You are going to need a K2PAKIT from Elecraft.  That kit includes a 
matched set of PA transistors (replace both) as well as replacements for 
Q11 and Q13 (also replace both).  After you install Q11 and Q13, but 
before you install Q7 and Q8, check the voltage on the base solder pads 
for Q7 and Q8 during a TUNE - it should be no higher than 0.64 volts and 
no lower than 0.61 volts.  If it is not in range, find the cause and fix 
that first so you do not zap the new PA transistors.

In addition to the PA transistors, check diodes D16 and D17 in the 
KPA100 wattmeter and also diodes D1 and D2 in the KAT100 wattmeter and 
replace them if there is any question about their health.  You might 
want to order 4 1N5711 diodes (Elecraft PN E560004) and arbitrarily 
replace them.

What normally happens with a static surge on the antennas is that the 
wattmeter diodes fail, and that causes the K2 to not sense the power 
output - the MCU in the base K2, thinking there is no power output, 
cranks up the drive to maximum possible, and that stresses the PA in the 
base K2.

Good prevention is to add a DC path across all your feedlines (a high 
value resistor - 5k to 50k will do or a 100 uHy choke of sufficient 
current capacity) to bleed off static charge and arrange any antenna 
switch to connect your K2 to a dummy load when not in use.  You can get 
static buildup on an antenna with no DC path across the feedline without 
lightning - wind, rain, or snow can also cause a significant static 
charge to build on the antenna.

73,
Don W3FPR


On 4/17/2013 8:58 PM, Tommy Mitchell wrote:
> I sent this to Elecraft support, but I thought I'd post it here too to see
> if the collective wisdom of the group might have anything to add.
>
> Tonight during dinner I noticed my K2/100 (w/ KAT100) was showing no noise
> on the S Meter.  I unplugged the headphones and could hear no signals at
> all, as if the antenna was disconnected.  If I tried to tune, the ATU would
> light up (sometimes) and it would run a tuning cycle, but I don't know if
> it was finding a match. No noise at all on the bands.
>
> I started taking the panels off and the next disconcerting bit was when
> bits of plastic started falling out.  Q11 and Q8 are both split in half
> with most of the body of Q11 loose in the chassis and the base side of Q8
> split from the collector & emitter.
>
> I had left my radio on this afternoon while I was a few doors up the hill
> working and we had a short thunderstorm.  There were no close strikes (very
> little lightning at all) but yeah, I should have disconnected things but
> didn't realize I had left it in that state.  A visual inspection doesn't
> show anything else obviously wrong aside from some slight scorch mark where
> Q11 went boom.  No traces look blown and there are no signs that any of the
> caps or resistors in that area are damaged.
>
> Aside from Q11 & Q8, are there other likely candidates for replacement or
> places to check?  The ATU & PA100 pass a visual inspection.  The storm is a
> pretty strong correlation, but are there any other likely scenarios that
> could cause this failure?
>
>