[K3] KPA500 glitch - firmware bug?

[Carl W Clawson]

The other morning I powered up the station to have a listen but left the
KPA500 off. The rear panel power switch was left on and I had powered the
amp off the night before by the front panel switch.

There was no signal getting from the antenna to the K3, evidenced by absence
of band noise on 160 m. I turned on the amp with the front panel switch and
then it connected the antenna. (Why did I turn the amp on, you ask? I was
going to poke a band button and try a different antenna.) Somehow the KPA500
had "powered down" with its T/R switch in the wrong state. I put "powered
down" in quotes because it's a software state, not an actual physical
disconnection of power.

I suspect that if I'd powered down at the rear panel, I would have had an
antenna. But I'll never know unless it happens again.

73, Carl WS7L
K3 #486 S/W V4.48
KPA500 #750 S/W V1.11

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[ke9uw]

I think the bypass is a real relay, are u thinking that the power to the relay was somehow on? I wonder if it's more likely that the relay contact was not quite conducting for receive. And turning on the amp cycled the relay wiping the contact.

Sent from my iPhone

On Apr 6, 2012, at 8:14 PM, "Carl Clawson" <[hidden email]> wrote:

> The other morning I powered up the station to have a listen but left the
> KPA500 off. The rear panel power switch was left on and I had powered the
> amp off the night before by the front panel switch.
>
> There was no signal getting from the antenna to the K3, evidenced by absence
> of band noise on 160 m. I turned on the amp with the front panel switch and
> then it connected the antenna. (Why did I turn the amp on, you ask? I was
> going to poke a band button and try a different antenna.) Somehow the KPA500
> had "powered down" with its T/R switch in the wrong state. I put "powered
> down" in quotes because it's a software state, not an actual physical
> disconnection of power.
>
> I suspect that if I'd powered down at the rear panel, I would have had an
> antenna. But I'll never know unless it happens again.
>
> 73, Carl WS7L
> K3 #486 S/W V4.48
> KPA500 #750 S/W V1.11
>
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> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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[Jack Brindle]

This is not quite true. Indeed, when powered off from the front panel, most of the amplifier has its power removed, and things are placed into a powered-down state. The micro controller on the front panel board remains powered so that it can accept power-on commands, but pretty much everything else is shut down.

It sounds like the bypass relay either was not contacting on the receive side properly or the antenna was somehow otherwise disconnected from the amplifier receive path to the K3. Are you sure the K3 was set for the antenna port the amplifier was connected to? When the KPA powers up, it sends a "KPA powered on" message to the K3 which can cause the K3 to make changes. Perhaps this is what caused the antenna to be connected?

More details, please…

Jack Brindle, W6FB


On Apr 6, 2012, at 6:14 PM, Carl Clawson wrote:

> The other morning I powered up the station to have a listen but left the
> KPA500 off. The rear panel power switch was left on and I had powered the
> amp off the night before by the front panel switch.
>
> There was no signal getting from the antenna to the K3, evidenced by absence
> of band noise on 160 m. I turned on the amp with the front panel switch and
> then it connected the antenna. (Why did I turn the amp on, you ask? I was
> going to poke a band button and try a different antenna.) Somehow the KPA500
> had "powered down" with its T/R switch in the wrong state. I put "powered
> down" in quotes because it's a software state, not an actual physical
> disconnection of power.
>
> I suspect that if I'd powered down at the rear panel, I would have had an
> antenna. But I'll never know unless it happens again.
>
> 73, Carl WS7L
> K3 #486 S/W V4.48
> KPA500 #750 S/W V1.11
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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[Carl W Clawson]

I had not intentionally been using other antenna ports on the K3. When I
shut the system off the night before, I had been receiving on the transmit
antenna just fine. It's possible that I inadvertently hit some button on the
K3, but whatever state I got into, it got fixed when I turned on the amp. It
surprised me ... I was expecting to be chasing down an antenna switch
problem or bad feedline.

I have an accessory DC supply that powers up and down with the same power
strip that runs the K3's DC supply. I turn that strip off after shutting off
the K3 by its front panel. One item powered by the accessory supply is a
remote antenna switch that grounds all the feedlines when it gets powered
off. But it's not interfaced to any band outputs or anything, just a rotary
switch on the desk that I didn't touch. That switch feeds 12 VDC directly to
relays in the switch box. No logic or other sensitive electronics is in that
circuit. The selected antenna is always connected as soon as the K3 gets
powered up. The KPA500 is not on a power strip. It's always plugged into a
live 240 VAC outlet.

That pretty well describes my antenna selection.

-- Carl

> It sounds like the bypass relay either was not contacting on
> the receive side properly or the antenna was somehow
> otherwise disconnected from the amplifier receive path to the
> K3. Are you sure the K3 was set for the antenna port the
> amplifier was connected to? When the KPA powers up, it sends
> a "KPA powered on" message to the K3 which can cause the K3
> to make changes. Perhaps this is what caused the antenna to
> be connected?
>
> More details, please.
>
> Jack Brindle, W6FB

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