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K2/100 KPA100: Cannot Adjust tPA, Stuck at 0C

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Ian Greenshields

K2/100 KPA100: Cannot Adjust tPA, Stuck at 0C

After repeating the power calibration on my K2 KPA100 due to low
output power, I found the CAL tPA function had reset to 0C and can no
longer be adjusted.

Having pressed EDIT from the CAL tPA display, the display shows tPA
0C, but turning the VFO knob has no effect on the display, it remains
resolutely at 0C.

Scanning the archives dug up a couple of similar issues, but no
solution. Has anyone seen this? Is the there a fix? Is my brain
disconnected & I'm doing something stupid (most likely scenario, I'll
admit)?

I'm now concerned that having fixed the output power, the fan won't
switch on when it's needed.

Any help appreciated.

73 Ian G4FSU
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Don Wilhelm-4

Re: K2/100 KPA100: Cannot Adjust tPA, Stuck at 0C

Ian,

Put the K2 into CW test mode (in CW, press and hold the MODE button),
set the power level to something above 11 watts - press TUNE and measure
the voltage at KPA100 U1 pin 5. The voltage will normally be close to
0.6 volts.

If the above measurement is correct and you still cannot adjust CAL TPA,
then I suggest that you replace the KPA100 MCU.

OTOH, If the measured voltage is substantially different than 0.6 volts,
check the KPA100 bias as instructed in the manual - if that is found to
be grossly incorrect, check R5, R6 and Q3 (refer to the schematic) to be
certain these components are receiving the proper voltages during
transmit (use CW TEST mode).

73,
Don W3FPR

Ian Greenshields wrote:

> After repeating the power calibration on my K2 KPA100 due to low
> output power, I found the CAL tPA function had reset to 0C and can no
> longer be adjusted.
>
> Having pressed EDIT from the CAL tPA display, the display shows tPA
> 0C, but turning the VFO knob has no effect on the display, it remains
> resolutely at 0C.
>
> Scanning the archives dug up a couple of similar issues, but no
> solution. Has anyone seen this? Is the there a fix? Is my brain
> disconnected & I'm doing something stupid (most likely scenario, I'll
> admit)?
>
> I'm now concerned that having fixed the output power, the fan won't
> switch on when it's needed.
>
>

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Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
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Elecraft web page: http://www.elecraft.com

Ian Greenshields

Re: K2/100 KPA100: Cannot Adjust tPA, Stuck at 0C

Hi Don, all,

Thanks for the help & suggestions. Pin 5 of U1 is 0.6v but CAL tPA cannot be
adjusted. Looks like the MCU on the KPA100 is faulty. I've ordered a new
one.

73 Ian G4FSU

On 10/04/2008, Don Wilhelm <[hidden email]> wrote:

> Ian,
>
> Put the K2 into CW test mode (in CW, press and hold the MODE button), set the power level to something above 11 watts - press TUNE and measure the voltage at KPA100 U1 pin 5. The voltage will normally be close to 0.6 volts.
>
> If the above measurement is correct and you still cannot adjust CAL TPA, then I suggest that you replace the KPA100 MCU.
>
> OTOH, If the measured voltage is substantially different than 0.6 volts, check the KPA100 bias as instructed in the manual - if that is found to be grossly incorrect, check R5, R6 and Q3 (refer to the schematic) to be certain these components are receiving the proper voltages during transmit (use CW TEST mode).
>
> 73,
> Don W3FPR
>
>
> Ian Greenshields wrote:
>
> > After repeating the power calibration on my K2 KPA100 due to low
> > output power, I found the CAL tPA function had reset to 0C and can no
> > longer be adjusted.
> >
> > Having pressed EDIT from the CAL tPA display, the display shows tPA
> > 0C, but turning the VFO knob has no effect on the display, it remains
> > resolutely at 0C.
> >
> > Scanning the archives dug up a couple of similar issues, but no
> > solution. Has anyone seen this? Is the there a fix? Is my brain
> > disconnected & I'm doing something stupid (most likely scenario, I'll
> > admit)?
> >
> > I'm now concerned that having fixed the output power, the fan won't
> > switch on when it's needed.
> >
> >
> >
>