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K2 Changes modes when pushing A/B

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John Oglesby

K2 Changes modes when pushing A/B

My recently built K2 - no options - exhibits an odd behavior. When I
push the A/B button it occasionally pauses for a moment like it is
thinking - and changes modes instead. This happens in every combination
I have tried, working split, or just changing from VFO A to B or B to A
or using REV. I have carefully tested this and I am positive that the
mode switch is not being touched, nothing appears to be flexing, and
there doesn't seem to be any other odd behavior.

I tried to look back in the reflector, but I can't seem to find a search
function in the archives - so is this a known issue, or have I found
some hidden feature?

Thanks & 73

John
N9RE

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Don Wilhelm-4

Re: K2 Changes modes when pushing A/B

John,

That sounds like there is some sort of path between the BANK1 and BANK2
signal lines on the front panel board.
Did you attempt to clean the board of solder flux? If so, you may have
left some residue on the board (likely under the switches) that now must
be completely cleaned, even if that means removing the switches.
The combination of flux and solvents can create conductive paths that
are very difficult to track down. Do not remove the flux, it is not
conductive (just looks messy). If you must clean off a really messy
looking area, do it with a bit of alcohol applied sparingly with a Q-tip
or other small swab and work in a small area at a time. Make sure you
get it all off in that area, as I indicated, leftover flux plus solvent
can be conductive.

If you did not attempt to clean the board, then look very carefully at
the soldering of U3. Reflow the solder adding a bit of solder (actually
you will be adding a bit of flux).

73,
Don W3FPR

On 7/30/2011 8:00 AM, John Oglesby wrote:

> My recently built K2 - no options - exhibits an odd behavior. When I
> push the A/B button it occasionally pauses for a moment like it is
> thinking - and changes modes instead. This happens in every combination
> I have tried, working split, or just changing from VFO A to B or B to A
> or using REV. I have carefully tested this and I am positive that the
> mode switch is not being touched, nothing appears to be flexing, and
> there doesn't seem to be any other odd behavior.
>
> I tried to look back in the reflector, but I can't seem to find a search
> function in the archives - so is this a known issue, or have I found
> some hidden feature?
>
> Thanks& 73
>
> John
> N9RE
>
> ______________________________________________________________
> 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
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Please help support this email list: http://www.qsl.net/donate.html

John Oglesby

Re: K2 Changes modes when pushing A/B

Don - Thanks for the e-mail. I didn't clean the board, so that's OK.
After I got your email, and the response of the reflector seemed to say
that this isn't a common issue, I started to look at the schematic
around U3. What I did notice is that the two switches share a common
data line (D4) to U2. There could be an issue with the pull-up voltage
on that line which might make if flaky across the Bank 1/Bank 2
transition. So I will take the K2 apart and check U2, U3 and the
resistor bank on D4.

Thanks for the suggestions.

73

John
N9RE

On 7/30/2011 2:44 PM, Don Wilhelm wrote:

> John,
>
> That sounds like there is some sort of path between the BANK1 and BANK2
> signal lines on the front panel board.
> Did you attempt to clean the board of solder flux? If so, you may have
> left some residue on the board (likely under the switches) that now must
> be completely cleaned, even if that means removing the switches.
> The combination of flux and solvents can create conductive paths that
> are very difficult to track down. Do not remove the flux, it is not
> conductive (just looks messy). If you must clean off a really messy
> looking area, do it with a bit of alcohol applied sparingly with a Q-tip
> or other small swab and work in a small area at a time. Make sure you
> get it all off in that area, as I indicated, leftover flux plus solvent
> can be conductive.
>
> If you did not attempt to clean the board, then look very carefully at
> the soldering of U3. Reflow the solder adding a bit of solder (actually
> you will be adding a bit of flux).
>
> 73,
> Don W3FPR
>

Don Wilhelm-4

Re: K2 Changes modes when pushing A/B

John,

Thanks for the reminder about the pullup resistors - check RP1 to be
certain pin 1 (the end with the dot) is at the same end as the "1"
silkscreened on the board. Most of the R-paks in the K2 can be swapped
end for end, but not that one.

73,
Don W3FPR

On 7/30/2011 3:49 PM, John Oglesby wrote:

> Don - Thanks for the e-mail. I didn't clean the board, so that's OK.
> After I got your email, and the response of the reflector seemed to say
> that this isn't a common issue, I started to look at the schematic
> around U3. What I did notice is that the two switches share a common
> data line (D4) to U2. There could be an issue with the pull-up voltage
> on that line which might make if flaky across the Bank 1/Bank 2
> transition. So I will take the K2 apart and check U2, U3 and the
> resistor bank on D4.
>
> Thanks for the suggestions.
>
> 73
>
> John
>