Field repair of blown K3 front end?

[w8fn]

Due to an unlucky combination of station configuration and a bad TX gain
calibration in my K3s (since corrected) I've managed to burn out
something in the front end chain in my second station K3. I've verified
the problem is in the signal path between the ATU inputs and the input
to the main receiver. The Sub receiver is working correctly when
connected via the AUX RF input connector, but dead in normal split mode.
I've had a look at the schematic and can see a couple of probable points
of failure.

But... I wonder if anyone else has encountered the problem and done a
successful field repair. I'd have no particular trouble replacing one or
two parts on the main board, but without a board layout it would take a
fair amount of effort to find the suspect parts. I'm also not interested
in completely dismantling the radio if that's what it would take to
effect the repair.

Has anyone else found and fixed such a problem? I'd be very interested
in hearing your experience.

73...
Randy, W8FN
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[Don Wilhelm-4]

Randy,

I suggest you contact K3support - they can likely give you a small
number of probable failure points.  That will allow you to choose field
repair or send it to Watsonville.

73,
Don W3FPR

On 3/12/2016 10:36 AM, Randy Farmer wrote:
> Due to an unlucky combination of station configuration and a bad TX
> gain calibration in my K3s (since corrected) I've managed to burn out
> something in the front end chain in my second station K3. I've
> verified the problem is in the signal path between the ATU inputs and
> the input to the main receiver. The Sub receiver is working correctly
> when connected via the AUX RF input connector, but dead in normal
> split mode. I've had a look at the schematic and can see a couple of
> probable points of failure.

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[Joe Subich, W4TV-4]

Randy,

Is the main RX dead all the time (when using only Main RX - Sub RX
off)?

Two quick things to check ...

1) if the Main RX is dead all the time and you have KXV3/A/B boards
    in each rig, swap them.  If the problem moves with the KXV3, the
    problem is most likely D5.

2) If the Main RX works if the Sub RX is off and you have KRX3 in
    in each rig, swap the SUB IN boards.  This eliminates an issue
    with T1 (the splitter) and D1/D2 T/R switch PIN Diodes.

The first thing to check is the KXV3 ... If you don't have a second
KXV3, check the schematics for bypassing the potentially defective
one (J66, pins 13 & 15 and pins 8 & 10).

73,

    ... Joe, W4TV


On 3/12/2016 10:36 AM, Randy Farmer wrote:

> Due to an unlucky combination of station configuration and a bad TX gain
> calibration in my K3s (since corrected) I've managed to burn out
> something in the front end chain in my second station K3. I've verified
> the problem is in the signal path between the ATU inputs and the input
> to the main receiver. The Sub receiver is working correctly when
> connected via the AUX RF input connector, but dead in normal split mode.
> I've had a look at the schematic and can see a couple of probable points
> of failure.
>
> But... I wonder if anyone else has encountered the problem and done a
> successful field repair. I'd have no particular trouble replacing one or
> two parts on the main board, but without a board layout it would take a
> fair amount of effort to find the suspect parts. I'm also not interested
> in completely dismantling the radio if that's what it would take to
> effect the repair.
>
> Has anyone else found and fixed such a problem? I'd be very interested
> in hearing your experience.
>
> 73...
> Randy, W8FN
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> 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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[Dave Hachadorian-2]

Here ya go:
http://marc.info/?l=elecraft&m=145323127930319&w=2

If you have the KXV3 installed, it is probably D5.  I checked the
Mouser part number for the heavy-duty replacement, and it's still
good.


Dave Hachadorian, K6LL
Yuma, AZ


-----Original Message-----
From: Randy Farmer
Sent: Saturday, March 12, 2016 8:36 AM
To: Elecraft
Subject: [Elecraft] Field repair of blown K3 front end?

Due to an unlucky combination of station configuration and a bad
TX gain
calibration in my K3s (since corrected) I've managed to burn out
something in the front end chain in my second station K3. I've
verified
the problem is in the signal path between the ATU inputs and the
input
to the main receiver. The Sub receiver is working correctly when
connected via the AUX RF input connector, but dead in normal
split mode.
I've had a look at the schematic and can see a couple of probable
points
of failure.

But... I wonder if anyone else has encountered the problem and
done a
successful field repair. I'd have no particular trouble replacing
one or
two parts on the main board, but without a board layout it would
take a
fair amount of effort to find the suspect parts. I'm also not
interested
in completely dismantling the radio if that's what it would take
to
effect the repair.

Has anyone else found and fixed such a problem? I'd be very
interested
in hearing your experience.

73...
Randy, W8FN
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[w8fn]

Excellent! Thanks to Dave, Joe and Don for the useful information. The
K3 is now on the bench and I'll start work soon. It most likely is D5 on
the KXV3.

Thank y'all for the quick response.

73...
Randy, W8FN

On 3/12/2016 9:43 AM, Don Wilhelm wrote:
> Randy,
>
> I suggest you contact K3support - they can likely give you a small
> number of probable failure points.  That will allow you to choose
> field repair or send it to Watsonville.
>
> 73,
> Don W3FPR

On 3/12/2016 11:24 AM, Joe Subich, W4TV wrote:

>
> Randy,
>
> Is the main RX dead all the time (when using only Main RX - Sub RX
> off)?
>
> Two quick things to check ...
>
> 1) if the Main RX is dead all the time and you have KXV3/A/B boards
>    in each rig, swap them.  If the problem moves with the KXV3, the
>    problem is most likely D5.
>
> 2) If the Main RX works if the Sub RX is off and you have KRX3 in
>    in each rig, swap the SUB IN boards.  This eliminates an issue
>    with T1 (the splitter) and D1/D2 T/R switch PIN Diodes.
>
> The first thing to check is the KXV3 ... If you don't have a second
> KXV3, check the schematics for bypassing the potentially defective
> one (J66, pins 13 & 15 and pins 8 & 10).
>
> 73,
>
>    ... Joe, W4TV

On 3/12/2016 11:32 AM, Dave Hachadorian wrote:
> Here ya go:
> http://marc.info/?l=elecraft&m=145323127930319&w=2
>
> If you have the KXV3 installed, it is probably D5.  I checked the
> Mouser part number for the heavy-duty replacement, and it's still good.
>
>
> Dave Hachadorian, K6LL
> Yuma, AZ

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[w8fn]

Must be D5. Removing the KXV3 and shorting pins 8 &10 and 13 & 15 on its
socket restores full sensitivity to the Main receiver. Thanks again, guys.

73...
Randy, W8FN

On 3/12/2016 1:32 PM, Randy Farmer wrote:
> Excellent! Thanks to Dave, Joe and Don for the useful information. The
> K3 is now on the bench and I'll start work soon. It most likely is D5
> on the KXV3.
>
> Thank y'all for the quick response.
>
> 73...
> Randy, W8FN

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