K2 trouble on the tracks

[richard gilley-2]

My K2 was operating fine, has the SSB module the latest addition, and  
The KTA100 addition.  Has been working fine for a week since the SSB  
addition. Was on 80 meters tuning up on low power, 3 watts, and the  
lights went out.
Removed the KTA100 and SSB board on QRP with power to min, press  
start: lights for 2 to 3 sec and quits.

Where is the best place to start?

Appreciate your help.
Best regards
Dick AD1G
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[Ron D'Eau Claire]

I'm sure our resident expert Don Wilhelm, will reply as soon as he sees the
message, but in the meantime check the resettable fuse (F1 I believe). From
what I've seen here some have failed. It sounds like your may be triggering
at a very low current level now, only allowing the brief periods of
operation before it opens, then it resets as it should after you switch off.

It's pretty easy to check with a DMM. When it opens the 12V should disappear
from one end!

Ron AC7AC



-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of richard gilley
Sent: Thursday, November 05, 2009 4:30 PM
To: [hidden email]
Subject: [Elecraft] K2 trouble on the tracks

My K2 was operating fine, has the SSB module the latest addition, and  
The KTA100 addition.  Has been working fine for a week since the SSB  
addition. Was on 80 meters tuning up on low power, 3 watts, and the  
lights went out.
Removed the KTA100 and SSB board on QRP with power to min, press  
start: lights for 2 to 3 sec and quits.

Where is the best place to start?

Appreciate your help.
Best regards
Dick AD1G
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[Don Wilhelm-4]

Dick,

That behavior is typical when the K2 is drawing too much current.  The
resettable fuse (F1) on the RF board (right edge) trips.  Please confirm
this by making the voltage measurement Ron suggested - if there is
voltage on one leg of the fuse, but not the other, that is confirmation
that the fuse is tripping.

IF the fuse is tripping, and IF you have a method of measuring the
actual current draw externally, check to see if the current draw is
coming close to 5 amps (the point where the resettable fuse trips).  If
indeed the current is high, the fuse is OK and you need to look for the
cause of the high current draw.

The normal cause of extremely high current draw is shorted PA transistors.
If you have good de-soldering equipment, you can remove those
transistors to check the current with them not installed.
BUT if you think you will have trouble removing the transistors intact,
then remove T3 (the bifilar wound toroid near the PA transistors).  
Removing that toroid will disconnect the 12 volts from the PA collectors
and allow you to check the remainder of the K2.  If you remove the
transistors or remove T3, you can safely operate the K2 without the heat
sink (do not try that with 12 volts on the PA transistors or they will
be damaged quickly).

73,
Don W3FPR

richard gilley wrote:

> My K2 was operating fine, has the SSB module the latest addition, and  
> The KTA100 addition.  Has been working fine for a week since the SSB  
> addition. Was on 80 meters tuning up on low power, 3 watts, and the  
> lights went out.
> Removed the KTA100 and SSB board on QRP with power to min, press  
> start: lights for 2 to 3 sec and quits.
>
> Where is the best place to start?
>
> Appreciate your help.
> Best regards
> Dick AD1G
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
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