[Elecraft] K2 - KPA100 down again

[Don Wilhelm]

Bill,

Remove the shield and give it a good visual inspection first - look for 
any evidence of overheated components.
Then check the diodes in the T/R switch - preferably with a diode test 
function of a DMM, but the ohmmeter will work too - check both the 
forward and reverse connections.
Check the 2 small diodes in the wattmeter section (T4 area) while you 
have the DMM set to measure diodes.

If you find something awry in the above tests, fix it, but if those 
tests/checks reveal nothing, proceed as follows:
If you are not driving a dummy load already, directly connect one to the 
KPA100 and try a quick test.  If you can get power on without blowing a 
fuse, then set the K2 in CW TEST mode and check the PA bias voltage - 
you should have 0.6 volts on the base of the PA transistors.
I it is still drawing a great amount of current, temporarily lift one 
end of Z1.  That will take the 12 volts off the PA transistors and allow 
you to see if something other than the PA transistors is causing the 
problem.

Tell us what you find and we can go from there.

73,
Don W3FPR

nz0t wrote:
> After performing flawlessly for over a year my KPA100 has died for the second
> time in about 3 months.  I was finishing a nice 20 minute QSO on 10M CW last
> week when the rig's lights flickered and the power supply shut down.  Now
> the power cord fuses blow and there appears to be a short when the power
> supply is turned on - even with the rig off.  The K2 itself is fine and
> works great QRP but I need help with what direction to take with diagnosing
> the KPA100 trouble.
> May be the KPA100 is upset that my K3 will be here in a couple of months and
> it and the K2 will no longer be center stage in the shack?
>
> Any and all help greatly appreciated!
>
> Bill NZ0T
>