[Elecraft] K2 after kat2 install Q7 & 8 check

[Don Wilhelm]

Russ,

At first glance it would appear that you have shorted PA transistors (at 
least one of them)

To address the problem, the first thing is to order the K2PAKIT from 
Elecraft.  It contains matched PA transistors, new PA transistor 
mounting hardware if you have the older white standoffs, replacements 
for Q11 and Q13 if needed, and a 1/2 watt resistor for replacement of 
R50 if your K2 has the older 1/4 watt resistor - there are new thermal 
pads for the PA transistors in the kit.

I strongly recommend that you proceed as follows:
1) Remove the heatsink - to keep from losing the PA mounting hardware, 
stick a 3/4 inch square of electrical tape over the screwheads - it can 
stick to the board and sides of T4.
2) Remove Q7 and Q8.  If you do not have good desoldering tools, cut the 
leads near the body of the transistors and remove the leads one at a 
time.  Clean up with solder wick and if solder remains in the holes, 
heat the solder pads and push it out with a wooden toothpick.
3) With A7 and Q8 removed, do a TUNE while measuring the voltage at the 
Q7 or Q8 base solder pads.  The voltage should be between 0.60 and 0.64 
volts.  If it is not, replace Q11 and Q13.
4) Once you have established that the base voltage for Q7 and Q8 is in 
the correct range, then you are good to install Q7 and Q8.  Use the new 
thermal pads and re-install the heatsink.
Before powering on, check the resistance from the Q7 or Q8 collector to 
ground.  It will climb as your DMM charges the electrolytic capacitors. 
If you see 1500 ohms or more, you should be 'good to go'.

If you still see zero ohms, then remove the heatsink again and check the 
thermal pads.  The heatsink could have some chards of metal on it, so 
hit it with some sandpaper.  Look for pieces of metal embedded in the 
thermal pad material.

You would be wise not to use the internal toothed lockwashers when 
reassembling because they can cause metal chips to be released.  You can 
use split #4 lockwashers instead, but be certain to tighten them securely.

73,
Don W3FPR