K2 Q7 Collector To GND Resistance Reading

[g.c.hart]

In running the final Resistance Checks on p. 71 of the K2 manual, I only get 1.7 ohms at the Q7 collector. The manual says I should get >500 ohms. When I study the schematic, I can't see where the >500 ohms is supposed to come from since Q3 is connected across Q7 and Q8 collectors and the 12V line.

Please help. Thanks.

Gary
N0AGH
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Masleid, Michael A.-2]

Hi Gary,

Yes, you are also looking at the 12 volt line.

Only 1.7 ohms is too low.  Look at your meter.  Is the "positive" lead
at Q7 - if not you could be "turning on" D12 on the 12 volt feed.  That's
a reverse polarity protection diode.  Also, the resistance readings don't
come out right if your ohm-meter puts out too much voltage.  The meter
should not make enough voltage to "turn on" semiconductor junctions.

If you really only have 1.7 ohms on the 12 volt line something is likely
to smoke.

>In running the final Resistance Checks on p. 71 of the K2 manual, I only
>get 1.7 ohms at the Q7 collector. The manual says I should get >500 ohms.

GL de AB9GV
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Don Wilhelm-3]

Gary,

You have a short (or at least a very low resistance) to ground somewhere in
the PA collector circuit or on the +12 volt line.

The easiest first step in isolating it is to remove the heat sink.  The tabs
on the PA transistors are connected to the collector, and the thermal pads
are supposed to act as an insulator as well as a heat transfer medium.  It
is quite possible that a bit of metal is lodged in the thermal pads, and the
best way to check that is to remove the heat sink (rear panel).

If the short remains after removing the heat sink, look very carefully at
the soldering in the PA area - it only takes a sliver of solder splash to
create a short.

73,
Don W3FPR

----- Original Message -----

> In running the final Resistance Checks on p. 71 of the K2 manual, I only
> get 1.7 ohms at the Q7 collector. The manual says I should get >500 ohms.
> When I study the schematic, I can't see where the >500 ohms is supposed to
> come from since Q3 is connected across Q7 and Q8 collectors and the 12V
> line.
>
>


_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com