Q7 Collector Short to Ground

[Steven Pituch]

Hi All,
I just finished all the mods to bring K2 #402 to the current standard.
I keep getting a collector short to ground when starting to tighten the
bolt going through the heat sink of Q7. Q8 is fine.  I have taken the
case off several times and inspected all the components.

Is there a trick to this, or do I need to order a new hardware set?

The plastic standoffs look a bit like truncated cones and the black
shoulder washers don't have much of a shoulder anymore. It has worked
for six years, but it might be time to replace the stuff.  I was hoping
to get it on the air today, but........

Regards,
Steve, W2MY
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[Don Wilhelm-3]

Steve,

Something is amiss with your measurement (or the K2 wiring, components,
etc.) if you show a collector to ground short on Q7 but not Q8.  Both T3 and
T4 provide a DC path from one collector to the other, so they should both
show the same resistance to ground.

Secondly, yes it is probably time to replace the mounting hardware - the
newer spacers are more stable, but for right now, you may want to
concentrate just on the thermal pads - they should be free of any tiny metal
chips that tend to break free when the screws and nuts are loosened
(assuming you used the internal toothed lockwashers) - I recommend using
only the split lockwashers on the output transistor mounting hardware and
the two adjacent screws that thread into the 2-D connector.

73,
Don W3FPR

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]]On Behalf Of Steven Pituch
> Sent: Saturday, June 04, 2005 3:55 PM
> To: Elecraft List
> Subject: [Elecraft] Q7 Collector Short to Ground
>
>
> Hi All,
> I just finished all the mods to bring K2 #402 to the current standard.
> I keep getting a collector short to ground when starting to tighten the
> bolt going through the heat sink of Q7. Q8 is fine.  I have taken the
> case off several times and inspected all the components.
>
> Is there a trick to this, or do I need to order a new hardware set?
>
> The plastic standoffs look a bit like truncated cones and the black
> shoulder washers don't have much of a shoulder anymore. It has worked
> for six years, but it might be time to replace the stuff.  I was hoping
> to get it on the air today, but........
>
> Regards,
> Steve, W2MY
> _______________________________________________
> Elecraft mailing list
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> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft
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[Steven Pituch]

W3FPR - Don Wilhelm wrote:
> Steve,
>
> Something is amiss with your measurement (or the K2 wiring, components,
> etc.) if you show a collector to ground short on Q7 but not Q8.  Both T3 and
> T4 provide a DC path from one collector to the other, so they should both
> show the same resistance to ground.

Yes Don, that is correct.  What I was doing was looking at the ohm-
meter as I was tightening each one of the screws.  As soon as the Q7
showed the short I would back off on the screw a turn.  That's why Q8
still looked good.  I can tighen down the screw for Q8 with no problem.

Regards,
Steve
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