K2: K2 #6996 is dead - please help!

[VK7JB]

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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[Don Wilhelm-4]

  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, [hidden email] 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
>
>
>
>
>
>
> ------------------------------------------------------------
> This email was sent from Netspace Webmail: http://www.netspace.net.au
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
>

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[Alan Davenport]

You may have blown the PA transistors. I had the EXACT same thing happen to me
(Dropped test lead) and that is what happened. Try removing T3. This will remove
power to the PA transistors and then try powering up. If you are lucky it should
power up fine. The PA transistors were $15 USD from Elecraft.

Good luck.

73 de Al, W2GZN




________________________________
From: "[hidden email]" <[hidden email]>
To: Elecraft Group <[hidden email]>
Sent: Sun, October 24, 2010 9:08:24 AM
Subject: [Elecraft] K2: K2 #6996 is dead - please help!

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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