hp65 hardware issue

[rias]

Help please!!!
I have a 65 that used to work fine. But now when I use mid key row, 8,5,2 it freaks out totally.
So like 7 , enter, 4, X, (28) then 9 , divide, (3.11)
Then press 8 , 5 or 2, and it gets wild, shows anything....
Bad contact somewhere, but where?

Replaced/New fresh battery, have opened it up a > 10 times, cleaned cards and contacts with electronic cleaner spray etc...

Sometimes it may work a few times, then goes back to jibberich when pressing 8,5,2 keys...

Some weak component? Any suggestion appreciated...