K2 resets in operation or TUNE selection - continuing problem

[wa4ywm]

This is an issue I have been dealing with for some time now and the
troubleshooting process has been complex so I will try to be specific about
my questions. Bear with me as I summarize the issue.

My K2/KPA100 performs a complete power reset when TUNE has been activated
for about 10 seconds. It indicates Hi Cur at that point. The radio has to be
on for approximately 2 hours before it exhibits this behavior.

This problem originally occurred in 2015. Don Wilhelm helped me troubleshoot
it and I thought a solution had been found. The problem showed up again in
2018 and Don worked with me extensively to attempt to resolve it to no
avail. Don finally threw in the towel on email troubleshooting and suggested
I try replacing components in suspect circuits which I have done.

Note that I have probably put in 100+ hours on this effort.

We narrowed the problem down to something in the SWR Bridge or the LPF since
it appears that the K2 is calling for more power than it can deliver
increasing the current until it resets.

With that very brief summary in place I will now ask some specific questions
which I hope will be picked up on by someone at Elecraft.

NOTE: DURING ALL THE TESTING THE KPA100 IS CONNECTED BUT WITH POWER SUPPLIED
THROUGH THE BASE K2 CONNECTOR.

I have measured the increase in current in TUNE when the Hi Cur event has
occurred. I broke the 12V supply circuit to the base K2 PA and associated
components to measure the current. During normal TUNE the current is 660mA.
During the Hi Cur event the current is 1.9A - an increase of 1.2A. The
current shown on the K2 display is 4A total.

1. What is the actual reset mechanism? I thought the re-settable fuse would
not trip until 5A was drawn. If it is re-setting, why at 4A?

2. Why is there a 10 sec delay from initiation of TUNE until the K2 resets?

3. Is there some other mechanism for reset (in the firmware?) in the K2?

4. I have replaced every active component in the SWR Bridge including twice
replacing the D16 & D17 diodes. I have removed and examined T4. What other
components should I look at replacing? This is assuming, of course, that the
problem is in the Bridge.

5. Is there something else that needs to be examined? Although I can't
imagine what hasn't been examined during the troubleshooting by Don and
myself.

6. A basic question - why is there a 2 hour period of power on before TUNE
causes a reset? Believe me I have examined this one over and over. I don't
expect an answer - just wanted to throw it out there.

NOTE: I HAVE PERFORMED ALL UPGRADES DURING THIS ENTIRE PROCESS INCLUDING THE
BASE PA UPGRADE.

NOTE: IF ANYONE WANTS TO TAKE THE TIME TO READ IT, I HAVE COMPILED AND
EDITED ALL OF OUR EMAILS INTO A MORE READABLE DOCUMENT.

I REFUSE TO LET THIS THING BEAT ME! THERE HAS TO BE A SOLUTION TO THIS!

Thanks for reading.

73,
Jim WA4YWM



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[Don Wilhelm]

Jim,

Troubleshooting steps to take - in order:
Powering only the base K2, connect a wattmeter and dummy load to the
KPA100 SO-239 jack.
Set the K2 power at 5 watts and do a TUNE.  What is the actual power
output?  If it is more than 12 watts, then the KPA100 wattmeter is at fault.
If the actual power is near 5 watts, then the KPA100 wattmeter is OK.

If the KPA100 wattmeter is performing OK, then:
Remove the KPA100 completely including all cables and test only the base
K2.  Connect the wattmeter and dummy load to the base K2 BNC antenna jack.

Do a TUNE and measure the voltage on the base of Q7 and Q8.  It should
be in the range of 0.60 to 0.64 volts.

Tap DISPLAY to show the voltage and current and do a solid keydown in CW
mode.  What is the current draw, and what is the actual power shown on
the external wattmeter?  Did the voltage shown on the K2 drop
significantly?  If the voltage is low, the K2 must draw more current to
develop power.  The voltage should not drop significantly and should be
above 12.7 volts with a power supply voltage of 13.8 or more.  If the
voltage drops significantly, check the power cord and its connections -
they should all be tight.

Turn the power up to 10 watts and keydown.  What is the current shown in
the K2 display?  If it is greater than 3 amps, check the number of turns
on the winding of T4 connected to the 3 and 4 leads.  There should be 3
turns.

Do those checks and let us know what happens.

73,
Don W3FPR



On 3/18/2019 10:06 PM, wa4ywm wrote:

> This is an issue I have been dealing with for some time now and the
> troubleshooting process has been complex so I will try to be specific about
> my questions. Bear with me as I summarize the issue.
>
> My K2/KPA100 performs a complete power reset when TUNE has been activated
> for about 10 seconds. It indicates Hi Cur at that point. The radio has to be
> on for approximately 2 hours before it exhibits this behavior.
>
> This problem originally occurred in 2015. Don Wilhelm helped me troubleshoot
> it and I thought a solution had been found. The problem showed up again in
> 2018 and Don worked with me extensively to attempt to resolve it to no
> avail. Don finally threw in the towel on email troubleshooting and suggested
> I try replacing components in suspect circuits which I have done.
>
> Note that I have probably put in 100+ hours on this effort.
>
> We narrowed the problem down to something in the SWR Bridge or the LPF since
> it appears that the K2 is calling for more power than it can deliver
> increasing the current until it resets.
>

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Please help support this email list: http://www.qsl.net/donate.html