[Elecraft] K2 PA

[Don Wilhelm]

Aaron,

Did you replace the PA transistor thermal pads?  And if so, did you 
smooth out and metal projections on the heat sink before installing the 
heatsink?  Those are necessary steps to prevent a short from the PA 
transistor tabs (also the collector) to the heatsink.

You must always do a resistance check from the Q7 and/or Q8 collector 
leads to ground after installing the heatsink.  If that check shows you 
a zero or very low resistance, then you need to investigate the cause - 
usually metal embedded in the thermal pads, or jagged edges on the 
heatsink where the heatsink contacts the thermal pads.

73,
Don W3FPR

On 4/28/2020 4:22 PM, Aaron K5ATG wrote:
> I just replaced the PA's on my K2. I replaced Q7, Q8, Q11, Q13 with parts
> from the Elecraft PA Replacement Kit.  I have done this in the past with no
> problems. Power is supplied from a switching power supply that supplies
> power to a power distribution box that has a fuse for each output. This
> distribution box supplies power to a small 2 meter 70cm mobile/base radio
> and a LED light strip. This setup has been working with no trouble for a
> while. Now as soon as I plug in the power cord to the K2 all of the power
> coming from the distribution box shuts off. I used the same power cord on
> two other radios and it worked just fine. So the problem lies in the K2.
> While working on the K2 I messed with replacing only the parts mentioned
> above. I went over the PA's with a magnifying glass looking for solder
> bridges and other faults and could not find any. This problem did not exist
> before I changed the PA's. I would appreciate any ideas as to what may be
> the problem.
> Aaron K5ATG
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