[KX3] PRE, ATT, MSG, CLR buttons stopped working..

[Geert Jan de Groot]

Hi,

A report on recent events with my KX3:
When I tried to use it yesterday, I found that several buttons
were no longer responding: PRE, ATT, MSG and CLR.

Tried power-off/on, no change. Removed the battaries for 5 minutes,
no change.

I was able to go to setup and started SW TEST so I could test the
front panel. Every button and knob was working, except for these four,
which didn't show up with the test.

Looking at the K3 schematics, these buttons all share the same SCAN103
going to pin27 of U10 on the front panel, the front panel processor.
Briefly, there is a voltage divider (R81, R80, R90, R89, R96)
and operating any of the four buttons should switch a different
voltage to SCAN103. This clearly worked for SCAN100, SCAN101, SCAN102,
SCAN104 but not for SCAN103. I was worried that the SCAN103 input was zapped.

Looking for people wo encountered this before, I found the blog from OK1RP
(http://ok1rp.blogspot.com/2019/05/no-response-from-msg-pre-and-attn-keys.html).
On the blog, the solution was to disconnect the flexfoil PCB between
control board and RF board, clean the contacts and re-install.
I checked the connectors - they were seated correctly as predicted in
the blog, I disconnected them, looked for dirty / corroded connectors,
and re-set it, and fortunately the issue was solved.
So, if others encounter this, Petr's blog may help.

But, I still wonder what had happened. The SCAN103 signal is not
connected to said connector and a bad contact cannot affect SCAN103.
SCAN103 only connects said buttons and the CPU, and that is all on
the control panel - no-where near to the interconnect connectors
with the flexfoil.

I wonder if an initialisation issue on the frontpanel processor U10
can have caused this?
Looking closer at the schematic, I see that the SCAN lines are completely
floating if a button isn't pressed. If nu button is pressed, the input
represents a high-impedance floating input. A static field (an operator
walking to the radi, and, without touching the radio first, opererating
one of the buttons) may perhaps cause an issue setting up the input.
I wonder why these pins don't have 100k to GND or so?

Perhaps the disconnect made power really disappear to do the recovery?
I noticed that my KXBC3 clock was running 20 minutes behind after
the operation - that is the time I worked on the issue, so just removing
the power isn't good enough to really drop all power.

I don't want to badmouth Elecraft, and I don't want to start a war
similar to the "yaesu IF filter discussion" of a few years back,
but I wonder if someone has done a more thorough investigation?
I note that adding resistors is easy (add them at the encoders)
and wonder if this is a change that has been implemented with newer
KX3 builds?

Comments?

73,

Geert Jan PE1HZG

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