[Elecraft] K2 resets in operation or TUNE selection - continuing problem

[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.
>