[Elecraft] K2 - KPA100 down again

[nz0t]

Thanks Don,
I checked the diodes and D12 and D14 in the switching circuit tested bad
along with D10 in the 12V line.  However when I took them out they all
tested OK.  I replaced them with new and now D12 and D14 tst OK in circuit
but D10 still shows bad but is OK once taken out of circuit.  Needless to
say the problem still exists.

Don Wilhelm wrote:
> 
> 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
>>   
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