Why did the keypad stop working? And is there anything that I can do at home to fix it myself?

In a word no. It uses a piezo electric transducer that works on a fixed frequency.

Manual

http://embed.widencdn.net/pdf/plus/cgi/wvto5w0yql/114a3026.pdf?u=gsn58x



It is a known issue. Toll Free number in the manual above

Some fixes here

https://www.google.com/search?safe=off&rlz=1C1QJDB_enCA643CA644&sxsrf=ALeKk02QBylJb4WeoaaWRR-KjNPoIe-_lA%3A1615141844957&ei=1BtFYMv6OaK2ggeRhLuICQ&q=chamberlain+940d-01+one+button+not+working



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Sounds like the micro processor has lost it program,
you can try this it might help.
Turn the fridge off and unplug it for a few minutes.
Then plug it back in and turn it on.
it should reassume and start working if it doesn't I'm afraid your going to have to place a service call with your local supplier

It sure sounds like the logic board has gone bad. You are doing everything right but the logic board is not learning the code.

http://www.samsungparts.com/search/search.asp

try to check all the accessories for your unit here

take to verizon to check it out....my keys stopped working (well, some of them) and they downloaded new software in 45 minutes and fixed it.....there was a glitch in the software when they originally came out with the phone and most times they can fix the problem

Have you checked the battery in the keypad itself? It is usually a specialty battery that you would need to purchase at a hardware store.

Hi,

Are you talking about the PIN code or the security code?

if you are good at opening then just open and check the keypad sensor might have got displaced ... if so then correctly place it ...

or may be the key pad buttons are not in contact correctly with the sensor board ...
if so just place it correctly & check whether the keypad is right or not ... if not replace with the good one ...
it will surely work ...

I am currently battling the same problem! The only key working on my keypad is the 'p' key, so I'm rather screwed. I've read many places online; however, that the problem is in the membrane underneith the keypad. Apparently it gets grimey or sand/dirt could get in it and it causes some of the keys to jam. You can purchase a new keypad here: http://performancepda.zoovy.com/c=1MywSpzr1JEqf54FSFslR8GzP/product/TREO650FLEXKEYBOARD if you're that interested. As for me, I'm prying the sucker apart to see if I can do it myself! Hope I was of help! xx Molee