[Elecraft] K3 Power Amp Shut Down Problem

[Don Nelson]

Don Wilhelm wrote:
> David and all,
>
> There already is a message for HI REFL which appears in the VFO B area 
> when the SWR exceeds 2.0.
> It is transient and could possibly be overlooked.  If a log of errors 
> could be made available, that might be helpful when troubleshooting.
>
> 73,
> Don W3FPR
>
> David Cutter wrote:
>   
>> That would be of great benefit if you had an intermittent fault, such as a 
>> fault in the antenna, particularly in a contest.  Antenna faults are 
>> probably the most common and an ERR message for high SWR sounds like a 
>> really good idea.
>>
>> David
>> G3UNA
>>   
>>
>>     
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>   

Don,

Interesting that you have a message reporting high SWR. I have never 
seen it and I have had MANY chances to see if it indeed does get 
displayed when a high SWR causes the power amp to be shut down.

Let's suppose for a moment that the mechanism that would display it did 
not get executed. What other mechanism in the firmware would shut down 
the power amp when I had the suspect cable connected and when the 
suspect cable is replaced with a presumed better cable, I have no power 
amp shut down? Am I to believe that there may be another problem? Any 
suggestions?

Don, N0YE



Here is a copy of my original post:

Hi all,

My K3 appears to be working just fine once the power amp shut down problem
was fixed. For months after I had assembled the K3, I would occasionally to
frequently experience power amp shut down failures. The power amp shut down
failures would occur while transmitting. The power amp shut down would occur
sometime after I had been transmitting for a while and sometimes when I has
been transmitting only for a very short time. This problem appeared to occur
mostly on the 10m band.

The problem appears to have been an intermittent BNC connector on the coax
cable that I was using. This cable worked fine on other radios but not the
K3. When I changed the cable to the K3, the power amp shut down problem went
away. I have been trouble free for about 6 weeks now.

Lessons learned: (a) use good cables with good connectors, (b) be aware that
the K3 has hair trigger protection logic that shuts down the PA, (c.) the K3
needs to have messages displayed on the front panel when it decides to shut
down the power amp giving a cause for that action, (d) the K3 documentation
needs to enumerate the actions the firmware may take to change the state of
the radio, in particular when the PA power is shut down.

Had I been able to read about the protection logic built into the firmware
to protect the power amplifier, I would have saved months of frustration
trying to figure out what was going on. It would be greatly appreciated by
me and surely many others if the user manual would discuss the protection
logic in the firmware and where and when power down actions will be taken.

Had the firmware reported protective action taken to shut down the power
amp, this too would have hastened my taking corrective action. It would be
so easy for the firmware to display, say on the VFOB display, that high SWR
caused the power amp to be shut down.

Don Nelson, N0YE