Iíve had the same problem with my ex XD3. The source of the problem is indeed the voltage, and the display board connector. The early production of XD series has a connector that connects the LCD board to the top panel board. This connector must be eliminated by soldering the LCD board directly to the top panel board. The second source of the problem is the voltage indeed. You are right with the 5.1 volts, but you should not adjust the potentiometer on the power supply board. It has been correctly adjusted from the factory. The problem again is the two white connectors at the both ends of the red bunch of wires that connects the power supply board to the main board. These two connectors will always fail due to oxidation. Again the ONLY remedy is getting rid of then. Solder the red wires directly to the boards. I did all these by myself, but if you feel that you donít have the skills, I advice you to ask a qualified person to do it for you.
You will never have any problems at all if you do BOTH operations. If your XD3 has been assembled after summer 2003, the LCD connector it should be already bypassed from the factory.
Hope my English was good enough. Should you require more explanations, do not hesitate to ask me.
Good luck! www.fantasyband.ro