I just recently had a similar problem...j720 keyboard was dead...no keys worked except power on and off. I had forgotten how easy it is to remove the keyboard by unscrewing the 3 anterior screws on the underside...but thanks to the HPCFactor soon found the teardown on it. I swapped out a keyboard working on a spare j720 of mine and it worked fine and reassured me the problem was not the motherboard.
What I found , in my case, was the space bar key had a misplaced bit of glue gun glue...something from a prior fix of mine...anyway it was trapped under the key cover and was continuously pressing down on the rubber key button underneath the key bar. The key covers are very easy to remove
(gently
) by prying up on the anterior edge of the key with a fingernail. I removed the glue glob and replaced it with some foam tape and voila...works fine now!
My best guess is you have some debris under the key cover that episodically interferes with the rebound of the underlying rubber button thing-y. Might want to check that out... The key cover is easy to re-install...just line it up in its proper place and gently press down and it will click into place.
Edited by joval 2020-04-14 5:01 PM
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