[Elecraft] K2 Q7 and Q8 Short to Ground

[Mark Yergin]

Don - The PA’s have never seen any power nor have I tried to transmit yet.
In the morning I’m going to take all the panels and boards off the RF board
and see if I still pass all the resistance checks.  I don’t understand how
I can pass the resistance check and then see this behavior when the boards
and panels are installed.

Mark W8EWH

On Sat, Jan 4, 2020 at 10:28 PM Don Wilhelm <donwilh at embarqmail.com> wrote:

> Mark,
>
> The most usual cause of a Q7/Q8 short to ground is that the thermal
> insulators are not installed properly.
> However, your statement that you see the same with the heatsink off
> indicates that the Q7 or Q8 transistors have been damaged by a collector
> to emitter short.  If the K2 was subjected to a transmit without the
> heatsink installed, that could be reason for the demise of Q7/Q8
> transistors.
>
> Make certain that the PA mounting hardware is installed correctly,
> especially the shoulder washers.
>
> 73,
> Don W3FPR
>
> On 1/4/2020 9:11 PM, Mark Yergin wrote:
> > I'm in the final stages of my K2 build, but having a problem with Q7 and
> Q8
> > shorting to ground.  When I did my Resistance Checks on pg 74, I had
> 3.66K
> > ohms to ground at the Q7 collector.  So that was fine.  But when I put
> all
> > the boards and panels on, then attached Q7 and Q8 to the heat sink, I see
> > about 135 ohms between the Q7 and Q8 collectors and ground.  I assume
> > that's unacceptable.  I see the same with the heat sink off.
> Suggestions?
>