Update:

--Removed the panel unit (selector buttons, control and relay boards)

--Visual inspection shows a zener diode (panel marking Z02) that has
overheating signs (black outline around diode.) The zener is 3/16 long,
with a diameter of a round toothpick and is much larger than other
zeners on the board.

Question: Does anyone know a way to determine proper zener replacement
visually?(markings, color codes etc.) Plan to replace this diode.

Recommendations: Manufacturer no help to this point--authorized
factory rep in local area has no listing for the Sharp R1810.
Thanks!