[Elecraft] K3s/KPA500 communication issue?

[Alan - G4GNX]

Mike, I'm not sure if this is relevant or not but I also have a tale of 
woe, similar to yours.

My main antenna is also an OSCFD and not really cut for 80 metres, so 
the SWR is always a bit higher than I prefer, possibly approaching 2:1.

My setup is a K3S + P3, KPA500 and KAT500.

A couple nights ago I was attempting to call a special event station in 
a pileup on 80 metres and decided to turn the KPA500 on. I was only 
running with around 11W from the K3S, giving me about 200W output from 
the KPA500.
After 'shouting' a couple of times, the SWR was just below 2:1 but the 
KPA500 didn't like it and suddenly faulted. When I tried to TX barefoot 
from the K3S, there was no output - nothing showing on the K3S display. 
I checked the power setting and it was 100W. I had previously power 
cycled the KPA500 and it was in Standby. The only way I could get the 
K3S to TX was to power cycle it, then all was back to normal.

I ran the KPA500 in Operate again for a few moments to check that it was 
OK and all seemed normal, but I didn't pursue it on 80m because I didn't 
want to push my luck. :-)

A couple days later on a regular 40 metre net, I ran the KPA500 again 
for over an hour (on SSB) and have had no issues.

I've not checked the manuals as to whether the original action is a 
safety feature or a bug.

73,

Alan. G4GNX


------ Original Message ------
From: "Mike Dodd" <mike at mdodd.com>
To: elecraft at mailman.qth.net
Sent: 14/11/2020 01:59:57
Subject: [Elecraft] K3s/KPA500 communication issue?

>Occasionally it seems my K3s doesn't know the STBY/OPER state of my KPA500. I also have a KAT500 for my Carolina Windom.
>
>Here's the first scenario: K3 in CW mode. I put the KPA in STBY and hit TUNE on the KAT and on the K3. When the tune is complete, I send one dash and note the 100W LED on the KPA. So far, so good.
>
>Next I put the KPA in OPER mode. The K3 power level is already set to about 10W, sufficient for about 250W on the KPA. Now I send a dash.
>
>Occasionally the KPA power indicator shoots up to 700W, and the KPA faults. When I clear the fault, the KPA is in STBY, and if I send a dash, I see the 100W LED come on. if I then put the KPA in OPER and send a dash, USUALLY I get the expected 250W output, but occasionally it shoots up to 700W and faults again.
>
>Now for the second scenario. With the KPA in OPER and outputting 250W, I switch it to STBY, then send a dash. I expect to see the 100W LED, but it does not light. If I look at the K3 RF bar graph, it shows 10W, not 100W. If I slightly turn the K3 PWR knob, it shows about 10W, not 100W.
>
>Until recently, the K3 ALWAYS switched back to my normal setting of 100W when the KPA is in STBY. The fact that it occasionally remains at 10W seems to indicate that it doesn't know the KPA is in STBY.
>
>Furthermore, the first scenario, where the KPA output shoots to 700W and it faults, seems to indicate that the K3 is sending it 100 watts -- another indication that the K3 doesn't know the KPA is in OPER, and thus doesn't reduce its output power to 10W.
>
>Is there any way to diagnose this problem, and more importantly, to fix it?
>
>Thanks for any and all guidance.
>
>-- 73, Mike N4CF
>Louisa County, VA USA
>Elecraft K3s / P3 / KPA500 / KAT500
>Carolina Windom up 45'
>http://n4cf.mdodd.com
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