Also check the motherboard crystal, this sets the frequency for lots of internal functions. Pull and re-seat it, make sure you get correct orientation.
Also check if the LEDS at the front of the machine are okay
If you have dismantled the machine a few times you can break the LEDS away from the small circuit board traces. If the traces are broken, repair with a circuit liner silver pen, or a car rear window defroster repair kit. It also has paint on electrically conductive silver paint.
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