I don't understand why the antenna being connected provided a path to
ground for the supply.
If that really is the case, there would seem to be a fault with your
power supply. The secondary (low voltage) side of a PSU should never be
connected to ground. Both poles should always 'float'.
I'd be very surprised if Elecraft had connected the negative supply to
chassis ground inside the KX3 either.
73,
Alan. G4GNX
------ Original Message ------
From: "Ian Liston-Smith" <ian...@hotmail.co.uk>
To: "elecraft@mailman.qth.net" <elecraft@mailman.qth.net>; "Mike Morrow"
<k...@arrl.net>
Sent: 05/09/2020 18:20:44
Subject: Re: [Elecraft] New KX3 reverse voltage smoke
In my haste to disconnect everything I didn't notice that the antenna was
connected, and thus the chassis had a good earth. On close inspection there is
a tiny burnt patch around the power supply plug and presumably that's what
created the smoke. So I guess the reverse current went through the plug
mountings on the board to earth and the reverse diode did its job.
There doesn't seem to be any serious damage to the board at the solder point to
the plug, just a black spot that joint took the full force of the shorted
current! I gently reheated that spot. Just hope there's not any overheated
damage to any internal tracks.
Anyway, seems no obvious harm was done. This KX3 still received and transmits.
I have now replaced most of the original lead with a proper, clearly coloured
red/black lead.
73,
Ian, G4JQT
________________________________
From: elecraft-boun...@mailman.qth.net <elecraft-boun...@mailman.qth.net> on behalf
of Mike Morrow <k...@earthlink.net>
Sent: 05 September 2020 16:26
To: elecraft@mailman.qth.net <elecraft@mailman.qth.net>
Subject: Re: [Elecraft] New KX3 reverse voltage smoke
The failure reported by G4JQT and the response of KC1DNY do not reflect what should happen when
reverse polarity DC is applied to the KX3 or any other Elecraft rig. All have that series blocking
diode (D6/CMS04 in KX3) that should prevent any significant reverse current flow and certainly
should have prevented "smoke" and "melted wire" from developing. If indeed
that is an accurate report, then an explanation from Elecraft should have been requested.
Something else aside from reverse polarity DC is being hidden in the picture
being presented so far.
Mike / KK5F
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