Ouch - An Update

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Ouch - An Update

Michael Lewis-3
So brought the K3 in to work this morning to our lab area where we have
static benches, blowers, wrist straps etc. and opened it up. Sure enough,
the T4 transformer was pretty crispy looking. My boss who is also an avid
ham (dream job setup :) ) then sprang into action. He removed the
transformer, counted the turns, removed the old wire, found some new magnet
wire of the proper gauge, rewound the toroid, and replaced both it and the
straight through portion (which had gotten pretty hot from the proximity to
the core.) Prior to stripping the burned turns off of T4 we looked at it
under a microscope and saw that the windings had burned open in one place,
effectively acting as a fuse of sorts. There didn't seem tpo be any other
parts, connectors, or board traces that looked to have been stressed. I
brought the radio home and hooked it up to a dummy load and a reasonably
accurate external wattmeter. It seems to be fine, both on receive and
transmit.

 

I was hoping there was a built in SWR bridge cal procedure, but I didn't see
anything like that in the manual. The SWR values reported though seem to
match the LP-100A I am using externally pretty closely. I did try to follow
the Wattmeter calibration and ran into some confusion on the procedure as
written in the manual. I think I was able to puzzle it all out except for
one item - how do you change the config menu item from CONFIG:WTMR LP to
CONFIG:WTMR HP? It doesn't seem to change just by having the tune power
changed to 50 watts, so I am at a loss on how to change it.

 

So perhaps my K3 is now alright again, although I would appreciate any other
comments on other things to check or calibrate. And thanks to all on the
list who helped me out. After this the next project is to fuse the DC supply
cables to my DC blocks with some rationally small value of fast blow fuse :)

 

de Mike/KE0MF

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Re: Ouch - An Update

Tony Estep
On Mon, Jun 30, 2014 at 9:40 PM, Mike Lewis <[hidden email]> wrote:

> ....My boss... then sprang into action. He removed the
> transformer, counted the turns, removed the old wire, found some new
> magnet wire.....
>
======
Mike, you have the right job, or at least the right boss!

Tony KT0NY
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Re: Ouch - An Update

vk2rq
In reply to this post by Michael Lewis-3
I'd suggest to replace the toroid core, as the high temperatures to which it was subjected may have altered the characteristics of the material.

73,
Matt VK2RQ

> On 1 Jul 2014, at 12:40 pm, "Mike Lewis" <[hidden email]> wrote:
>
> So brought the K3 in to work this morning to our lab area where we have
> static benches, blowers, wrist straps etc. and opened it up. Sure enough,
> the T4 transformer was pretty crispy looking. My boss who is also an avid
> ham (dream job setup :) ) then sprang into action. He removed the
> transformer, counted the turns, removed the old wire, found some new magnet
> wire of the proper gauge, rewound the toroid, and replaced both it and the
> straight through portion (which had gotten pretty hot from the proximity to
> the core.) Prior to stripping the burned turns off of T4 we looked at it
> under a microscope and saw that the windings had burned open in one place,
> effectively acting as a fuse of sorts. There didn't seem tpo be any other
> parts, connectors, or board traces that looked to have been stressed. I
> brought the radio home and hooked it up to a dummy load and a reasonably
> accurate external wattmeter. It seems to be fine, both on receive and
> transmit.
>
>
>
> I was hoping there was a built in SWR bridge cal procedure, but I didn't see
> anything like that in the manual. The SWR values reported though seem to
> match the LP-100A I am using externally pretty closely. I did try to follow
> the Wattmeter calibration and ran into some confusion on the procedure as
> written in the manual. I think I was able to puzzle it all out except for
> one item - how do you change the config menu item from CONFIG:WTMR LP to
> CONFIG:WTMR HP? It doesn't seem to change just by having the tune power
> changed to 50 watts, so I am at a loss on how to change it.
>
>
>
> So perhaps my K3 is now alright again, although I would appreciate any other
> comments on other things to check or calibrate. And thanks to all on the
> list who helped me out. After this the next project is to fuse the DC supply
> cables to my DC blocks with some rationally small value of fast blow fuse :)
>
>
>
> de Mike/KE0MF
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
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Re: Ouch - An Update

Jim Brown-10
On 6/30/2014 7:56 PM, Matt VK2RQ wrote:
> I'd suggest to replace the toroid core, as the high temperatures to which it was subjected may have altered the characteristics of the material.

Ferrite materials have to get pretty hot for that to happen. My guess is
that the thermal mass might be large enough that the wire fried before
that point. It might be worth asking Elecraft, but I'd take the approach
that if it ain't broke, don't fix it. :)

73, Jim K9YC


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Re: Ouch - An Update

Robert Friess
Congrats Mike,

Bob, N6CM


On Mon, Jun 30, 2014 at 8:55 PM, Jim Brown <[hidden email]>
wrote:

> On 6/30/2014 7:56 PM, Matt VK2RQ wrote:
>
>> I'd suggest to replace the toroid core, as the high temperatures to which
>> it was subjected may have altered the characteristics of the material.
>>
>
> Ferrite materials have to get pretty hot for that to happen. My guess is
> that the thermal mass might be large enough that the wire fried before that
> point. It might be worth asking Elecraft, but I'd take the approach that if
> it ain't broke, don't fix it. :)
>
> 73, Jim K9YC
>
>
>
> ______________________________________________________________
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> Please help support this email list: http://www.qsl.net/donate.html
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>
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Re: Ouch - An Update

mcduffie
In reply to this post by Michael Lewis-3
On Mon, 30 Jun 2014 20:40:45 -0600, Mike Lewis wrote:

> He removed the
> transformer, counted the turns, removed the old wire, found some new magnet
> wire of the proper gauge, rewound the toroid, and replaced both it and the
> straight through portion (which had gotten pretty hot from the proximity to
> the core.)

From experience, I can tell you that it is likely that the toroid was ruined by
the heat.  Once you heat it, the value changes, permanently, even if you replace
the wire.  I cooked a few in antenna tuners back in the 80s, before I learned
the cause.

I'd recommend you order a replacement (probably not expensive) and replace it at
your earliest convenience.  Also check with Elecraft about what other parts you
should check.  Be sure to tell them what happened, so they can accurately
estimate what issues you could have caused.

Gary - AG0N
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