[Elecraft] K3: reverse 12 volt supply

[roger wood]

A quick note to close off this string:

(It did diverge from the topic a bit, but now I know why black was cold in
the UK but hot in the US!)

Thanks for all the responses and good advice.  Much appreciated. I can see
there's pros and cons to the various suggestions.

I opened the box this weekend and found only two visible effects:

1) There is a slight discoloration of one portion of the traces that carry
the current to the 100W PA interface.  This is on the main RF board.

2) The encapsulation of the 5 milliohm current sense resistor on KPIO3 PA
interface had shattered. It must have had ~100 Amps through it!  Amazingly
it survived as a resistor, though it's dropped to 4.3 milliohms now.  So
that wouldn't have stopped the PA working or explain the over-current
warning. The sense amplifier itself is surface mount so that's beyond my
skill level.

There is no visible damage on the power amp card itself, I tried to check
some of the diodes and inductors etc. in situ, - but nothing obvious.  I
can't find up-to-date schematics for the KPA3A, which makes it difficult to
debug further.  Based on the older KPA3 schematics, I assume there's a
reverse shunt diode somewhere on the board. I see the circuit breaker &
diode are positioned after the current sense circuit rather than before,
which seems odd.

Anyhow, at this point I'm giving up.  I'll contact Elecraft and see if
they're willing to look at it. Hopefully it won't cost an arm and a leg.
I'm certainly very chastened by the experience.  It won't happen again!

Thanks again for the comments and advice.

73
Roger
KK6RW/G3WEW



On Wed, Sep 16, 2015 at 2:10 PM, Mel Farrer via Elecraft <
elecraft at mailman.qth.net> wrote:

> Here is where I got my color coded heavy wire.  Marine Wire | Marine
> Electrical | West Marine
>
> |   |
> |   |   |   |   |   |
> | Marine Wire | Marine Electrical | West MarineEmail Us Shipping
> Information International Shopping Returns & Exchanges Customer Service
> Call (800) 262-8464Monday-Friday, 8am - 9pm ETSat, 9am - 6pm ET; Sun,
> Closed  |
> |  |
> | View on www.westmarine.com | Preview by Yahoo |
> |  |
> |   |
>
>
>
> I am sure other marine supply houses do also.
> Mel, K6KBE
>
>       From: Bob McGraw - K4TAX <rmcgraw at blomand.net>
>  To: elecraft at mailman.qth.net
>  Sent: Wednesday, September 16, 2015 1:49 PM
>  Subject: Re: [Elecraft] K3: reverse 12 volt supply
>
> I checked the rolls of wire at the shop.  I find I have two different
> ones:
>
> Belden # 8720 -
> 14 AWG stranded (19x27) TC conductors, polyethylene insulation, twisted
> pair, overall Beldfoil® shield (100% coverage), 16 AWG stranded TC drain
> wire, PVC jacket.
>
> Belden # 8718 -
> 12 AWG stranded (19x25) TC conductors, polyethylene insulation, twisted
> pair, overall Beldfoil® shield (100% coverage), 14 AWG stranded TC drain
> wire, PVC jacket.
>
> 73
> Bob, K4TAX
> K3S s/n 10,163
>
>
> On 9/16/2015 11:20 AM, Richard Fjeld wrote:
> >
> > Thanks for all the replies with sources to find stranded, paired
> > wire.  I saved them all.
> > My sources suddenly quit. I feared the wire mfg's may have gone
> > off-shore, and I might have to use pastel colors (tic).
> >
> > And finally, FWIW, it seems someone is using my callsign.  If you
> > Google it, you will see scores of pictures being posted to it on
> > social media sites.  I have had QSL cards in error also.
> > It not me, folks.
> >
> > Trashed, or not, I hope to celebrate 40 years with this call next
> > year.  I received the ARRL WAS Bi-Centennial certificate in '76
> > shortly before receiving this call in the mail.
> >
> > Thanks for the bandwidth and 73,
> >
> > Dick, n0ce
> >
> > __
> >
>
>
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