[Elecraft] K2: K2 #6996 is dead - please help!

[Don Wilhelm]

  John,

I suspect you created a base to emitter short on Q7 - it only takes a 
millisecond or so for the transistor to be destroyed.
You can remove T3 which takes the +12 volts off the Q7/Q8 transistors 
and see if everything else is normal (of course, there will be no RF 
output).

If removing T3 fixes most everything, order the K2PAKIT from Elecraft.

73,
Don W3FPR

On 10/24/2010 9:08 AM, zendoc at netspace.net.au wrote:
> Hi All,
>
> K2 #6998 has had a short life.  Working  perfectly with KSB2/KDSP2/KNB2 all
> installed until tonight.
>
> I decided to tweak one of the BFO settings, connected the frequency counter to
> the control board and was about to connect it to the BFO test point on the RF
> board, when I dropped the tip into the vicinity of Q6/Q7 - can't say exactly
> where it landed, but I heard a click and the K2 went dead.  I waited a few
> minutes and powered up again, thinking the resetting fuse might have tripped.
> Now the K2 starts, the Elecraft initialisation appears, the frequency readout
> appears, and by this time (3 seconds or so) the self-resetting fuse gets hot and
> the K2 shuts down.
>
> I guess I have a short.  No visible evidence of where - I took the K2 apart to look.
>
> Resistance tests on the front board and control boards are all OK.
>
> Resistance tests on the RF board are no longer normal:
>
> Q7 base resistance to ground = 538ohm (ref 2.5 - 3.0kohm)
> Q7 collector  resistance to ground = 400ohm ( ref>  500ohm)
>
>
> Other measurements:
>
> Q6 base resistance to ground = 119 ohm,  collector 475 ohm,  emitter short to ground
>
> Q8 base resistance to ground = 538ohm,  collector 473 ohm,  emitter short to ground.
>
> I'd be grateful for any advice how to proceed from here.
>
>
> This is in the category of bad things to happen!  And the KPA100 is nearly
> finished :(
>
> Thanks and 73,
>
> John
> VK7JB
>
>
>
>
>
>
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