Microwave. keypad has two vertical rows of buttons. the left side work but none of the right side

Question

keypad has two vertical rows of buttons. the left side work but none of the right side which includes the start button. The unit has not got wet. Circuit board shows no obvious fault. Have reseated the mylar ribbon cable from board to keypad. Seems therefore that no voltage is getting to the right side or there is a fault in the keypad. However to ohm meter check the keypad would neccesitate knowing which buttons are on which of the mylar ribbon lines in order to prove a keypad fault.