[Elecraft] New KX3 reverse voltage smoke

[Alan - G4GNX]

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.ls at hotmail.co.uk>
To: "elecraft at mailman.qth.net" <elecraft at mailman.qth.net>; "Mike Morrow" 
<kk5f at 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-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> on behalf of Mike Morrow <kk5f at earthlink.net>
>Sent: 05 September 2020 16:26
>To: elecraft at mailman.qth.net <elecraft at 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
>