K2 - starts in transmit mode

[James C. Hall, MD-2]

Hello:

 

I hadn't started up my K2/100 in awhile and I wanted to give it some
exercise today. When I hit the power button, I was surprised to see it in
transmit mode with a hum/tone coming from the speaker. I immediately shut it
down, disconnected everything and hooked up a battery and a dummy load and
set the power to minimum. Pushing the power button revealed the same
symptoms - increasing the power showed the LED power meter increasing in
power until it got close to 100 watts and then showed Hi Cur. I powered down
and then shut it off.

 

I don't know what to try next, that is before attempting to do a MCU reset.
Any ideas would be appreciated.

 

73, Jamie

WB4YDL

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[Don Wilhelm-4]

  Jamie,

There are several possible causes, so the first thing you should do is
remove the KPA100 completely from the base K2.  That will get the output
power down to something more reasonable and allow you to do the
measurements that will eventually lead to tracking down the source.
After removing the KPA100, power the K2 from the coaxial power jack on
the rear panel and connect a good dummy load to the ANT jack.  Be
prepared to make some voltage measurements - your DMM black lead on a
grounding point.  Locate the anodes of D6 and D7 about halfway back and
an inch from the left side panel - power the K2 on and quickly turn the
power knob to between 3 and 5 watts (if you can).

Measure the DC voltage at the anode of both D6 and D7.  If both are
between 7 and 8 volts, turn off the K2 as soon as possible - it has both
transmit and receive turned on at the same time, and that can overheat
components - the rest of the measurements must be done in short spurts
to avoid damage.
Let us know if this condition exists and we will give you more
measurement points on the Control Board.

If D6 anode is at a low voltage but D7 has 7 to 8 volts, the K2 is
definitely in transmit and of course, the cause must be discovered.  
Measure Control Board U6 pins 29 and 30.  With nothing plugged into the
key jack and nothing plugged into the mic jack, these points should be
near 5 volts.  If one or both are near zero volts, you have an
electrical condition grounding one or both of those lines.  Power off
and let us know, the next steps are resistance measurements on the
/DOT-PTT line and the /DASH line.

73,
Don W3FPR

On 7/15/2011 5:59 PM, James C. Hall, MD wrote:

> Hello:
>
>
>
> I hadn't started up my K2/100 in awhile and I wanted to give it some
> exercise today. When I hit the power button, I was surprised to see it in
> transmit mode with a hum/tone coming from the speaker. I immediately shut it
> down, disconnected everything and hooked up a battery and a dummy load and
> set the power to minimum. Pushing the power button revealed the same
> symptoms - increasing the power showed the LED power meter increasing in
> power until it got close to 100 watts and then showed Hi Cur. I powered down
> and then shut it off.
>
>
>
> I don't know what to try next, that is before attempting to do a MCU reset.
> Any ideas would be appreciated.
>
>
>
> 73, Jamie
>
> WB4YDL
>

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Elecraft mailing list
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Help: http://mailman.qth.net/mmfaq.htm
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Please help support this email list: http://www.qsl.net/donate.html