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Kitchenaid f2e1 error / membrane keypad question


I'm working on a Kitchenaid KEBC107 oven that has an intermittent f2e1 error.  The customer purchased a replacement control board and the error persists, and called me.  I've read every post I can find on this error in any model oven.  I realize the KAC-28 service manual(for my model) indicates this error means "Keypad keytail not connected".  I tried the insertion of a piece of cardstock to improve the connection of the flex ribbon to the control board but still the problem persists.  Also cleaned the ribbon contact area with an eraser.  Checked for hairline cracks both physically and electrically.  Still has the problem intermittently.  Can occur when I go to press a key or all by itself when it otherwise is working properly!   :(

The short answer is replace the membrane keypad which is probably what I'll end up doing.  Big $$$.  However, the engineer in me is looking for more information if one of you may have insight into this problem to this level.  I hate to just change parts without understanding the root cause.  If you are not interested, then stop reading now!

I pulled the control board and keypad to work on it in my lab.  I see no damage and checked for shorted keys.  Infinite resistance between each line and every other line of the keypad.  The KAC-28 manual does not give a table of which key closes which lines but with some experimentation I can see what is connected to what when I press a button.

Finally, I come to my question...  Unless there is some built in resistance between at least two of the lines, there is no way for the controller to determine when the flex cable becomes disconnected. (remember, there is infinite resistance between all lines when no key is pressed)  Hence my confusion over the error code description.  How can the controller determine the keypad is disconnected?  (btw, if you're thinking it uses some capacitive sensing technique, I doubt it based on my examination of the control board)

I'm going to run a test with the control/keypad reinstalled in the oven.  I'll start the oven (assuming it doesn't error out immediately), and pull the keypad flex cable out of the control board and see if it causes the error.  My hypothesis is that it will NOT error out.  If it does error out each time, then I'll have to admit defeat and declare that I truly don't understand how the controller knows the keypad is there.  Geez, I might have to put an oscilloscope on each keypad line and see what's really going on!!!

I believe other models use the f2e1 error code to indicate a shorted or stuck key.  I understand how the controller can figure that out.  For my model, the f2e0 code is used for a shorted key and that's not the error I have.

So... I'd appreciate any insights any of you might have on this.  Sorry for the lengthy description!

Just a quick follow up.  I ran the test as I described, and as I suspected, the oven did NOT error out when I removed the membrane switch ribbon cable from the control board while the oven was operating properly.  It sat there fat, dumb, and happy on BAKE @ 350 and didn't error out! 

I am going to replace the membrane switch as prescribed by the KA support folks with the proviso that if the problem persists, I can return it and the new control board the customer obtained and get a new control board.  Then maybe we'll get this thing running properly! 


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