[Elecraft] [K2] KPA100 Temp Cal: Room temp or radio temp?

Sun Mar 27 18:27:38 EDT 2016

Mike,

First, the menu CAL TPA parameter will indicate the temperature of the 
heatsink if all is working normally.  That is why you let the heatsink 
cool to ambient temperature before setting CAL TPA.  If you have a 
temperature probe that can measure the heatsink temperature at the PA 
transistor mounting point, you don't have to let it cool to ambient, 
just set it to the actual heatsink temperature - but most hams do not 
have accurate temperature measurement equipment, so cooling to ambient 
is the normal procedure.
Set CAL TPA first before proceeding with anything else.

Did you purchase this KPA100 as a new kit or did you purchase it used?
It may have a fault or a badly soldered connection that changes when the 
temperature rises - but I suspect you may have a power control problem.

Make a check on the power output - connect it to an external wattmeter 
and a dummy load.
Set the power level for 50 watts and do a TUNE - the power on your 
wattmeter and the K2 display should indicate about 20 watts.
If you see 20 watts on both the K2 display and the external wattmeter, 
then proceed and do a TUNE/DISPLAY - in other words, depress both the 
TUNE and DISPLAY buttons together.  You should see about 50 watts 
indicated on both the external wattmeter and the K2 display.

If either or both those tests fail, I suspect you will see a low power 
indicated on the K2 display while seeing a high power (120 watts or 
greater) on the external wattmeter.
What that means is you have no power control and the KPA100 is going to 
its fully capable output at all times.
The cause of that behavior is damaged diodes in the KPA100 wattmeter - 
diodes D16 and D17 located on the board close to the SO-239 jack.

In other words, if your KPA100 is going to full power output all the 
time, it will heat rapidly and give you a PA HOT message.  More common 
is a HiCURR message, but if you have the CAL CUR set above 3.50 amps, 
you may not get that warning.

If the power control is working normally, then you should look into the 
PA Bias and the temperature sensing transistor Q3 or its input to the 
Firmware IC U1.

Yes, it is OK to turn power off or even to pull the power plug, that in 
itself will not cause a problem with the K2 - the K3 and KX3 are 
different in that respect, and they should be powered off normally.

73,
Don W3FPR

On 3/27/2016 5:24 PM, mjpilgrim wrote:
> I have a related question: I purchased my K2/100 only a month ago, second
> hand, SN 5818.  I've experienced "PA HOT" shut down on several occasions
> when running 100Watts out, and less frequently but it has happened when at
> 50Watts.  I've witnessed the discussion of setting Cal tPa to ambient temp.
> C, and with my indoor/outdoor digital weather monitor on my operating desk,
> I see 81 F as a normal workstation temp, which converts to 26.95 C......
> that is the figure I enter into the Cal tPa setting.  I can then operate CW
> for a few minutes, noticing that the fan does turn on.  Unfortunately, since
> I do not continually keep my eyes on the digital display as I continue my CW
> qso, I have been frequently surprised to note that I have experienced a Pa
> Hot failure and my output has shut down (although the side tone monitor
> continues to yield my keyed side tone).
>
> I have now noticed that when that failure occurs, I can power down the K2
> and immediately power it pack on, and I then can continue operating with
> full output power.  This almost appears as if the Pa Hot error is a false
> indication, and even though it initially shuts down my output power, it
> seems strange that it resets to normal ops when power is cycled off and on
> again.  I have failed to notice if the fan comes on upon the power off/on
> recycle..... I'm thinking it is not on at that time.  I'll try to be more
> observant on future failures but in the meantime I wanted to mention this
> failure in case I am overlooking something or maybe doing something to
> create harm by powering off and on the K2.
>
> PS.  While attempting to change the failing conditions, I have increased the
> Cal tPa temp up to as high as 33C, and I believe that is where it was set
> with my most recent failure.
>
> Any ideas out there?  Thanks.
> Mike, K5MP
>
>
>
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