[Elecraft] K2 Changes modes when pushing A/B

[John Oglesby]

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
>