[Elecraft] New KX3 reverse voltage smoke

[Ian Liston-Smith]

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

-----Original Message-----
>From: David Haines <dhaines at bates.edu>
>Sent: Sep 5, 2020 9:17 AM
>
>Don't feel bad Ian.  I reversed the polarity from the power supply, too.
>   After the smoke cleared and the smell went away, I called Elecraft
>and after a few questions, service said send in my KX3. They called in a
>couple days to thank me for sending the melted wire, but why did I send
>the KX3, which was fine?   They apologized, checked out the KX3,  and
>gave me a free replacement wire.  Great company!
>
>david,  KC1DNY
>
>On 9/5/2020 10:06 AM, Ian Liston-Smith wrote:
>> Well I did it. Inadvertently got the +ve and -ve reversed. Loud buzz from PSU and smoke from KX3.
>>
>> Surely D6 in the volts input should just stop everything from working if the polarity is reversed? So I don't understand what has happened.
>>
>> I didn't actually switch it on so hopefully it isn't terminal and just enquires a new diode. If it is terminal, I'm really surprised it hasn't any protection.
>>
>> Ian, G4JQT
>> ______________________________________________________________
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