[Elecraft] K3 power switching.

[Fred Townsend]

Alan the power circuit on the K3 is very robust and is protected from over voltage. There is a 15 volt zener that should trip a self resetting 6A fuse. It may be that zener over heated and shorted but even so there should not be smoke.

I agree your psu should be set so it can not exceed 14.8 volts.

73
Fred, AE6QL

-----Original Message-----
>From: G4GNX <G4GNX at theatreorgans.co.uk>
>Sent: May 11, 2015 3:36 AM
>To: Elecraft Reflector <elecraft at mailman.qth.net>
>Subject: Re: [Elecraft] K3 power switching.
>
>I'm going to bring this up at the next discussion evening. We should be able 
>to disable the voltage control pot, or replace it with a fixed resistor.
>
>The guy in question is actually very knowledgeable, so it's just bad luck 
>this time. Even if we'd 'fixed' the PSU, it may have developed the fault 
>anyway.
>
>73,
>
>Alan. G4GNX
>
>-----Original Message----- 
>From: Robert Wood
>Sent: Sunday, May 10, 2015 9:22 PM
>To: 'G4GNX'
>Subject: RE: [Elecraft] K3 power switching.
>
>after the fact this is clear but we don't allow variable voltage power
>supplies at club
>too many fumble fingers with membership over 100 and no telling who shows up
>at Field Day!!
>
>73 W5AJ
>
>
>-----Original Message-----
>From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of G4GNX
>Sent: Sunday, May 10, 2015 1:43 PM
>To: Elecraft Reflector
>Subject: [Elecraft] K3 power switching.
>
>Following a mishap with a PSU, our local club's K3 is in need of repair and
>I don't want anything similar to happen to mine.
>
>The PSU is a linear device with a voltage control potentiometer and a meter.
>The operator had an issue with the PSU which was showing an output of 15
>volts; the K3 was connected and working. He switched off the PSU to
>'exercise' the potentiometer and unfortunately turned it back on with the K3
>still connected and switched on. The reading was still 15 volts, so he
>touched the potentiometer again and the K3 started to emit smoke and died.
>At this time, we're assuming that the PSU grossly over-volted.
>
>My question: is the power switch on the K3 mechanical? If it is, then my
>fears will not be realized because I ALWAYS turn on my PSU AND check the
>output voltage on its meter before turning on the K3.
>
>It will be interesting to find out what died in the K3. I hope it's not too
>expensive.
>
>73,
>
>Alan. G4GNX
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