Yamaha DGX-620 blank screen or screen with vertical lines

I`ve had a similar problem with a Korg that I use at the club and on gigs, I don`t know whether Yamaha use a similar method or not but when I stripped mine down, I found that the glass LCD panel is connected to the PCB via a ribbon cable which gets sandwiched between the PCB and the LCD panel when screwed up, It`s not soldered or hard wired to the PCB, It was producing intermittent connections between the uPC and the display panel where parts of letters and symbols were missing. When I removed the panel, I found that it was oxidized so I used some switch cleaner which doesn`t leave a residue (Don`t use lubricant or WD40 as this will destroy the LCD panel by penetrating between the layers of Liquid Crystal rendering it useless) and gently cleaned the contacts on both the LCD and PCB panels (Don`t spray the panel or this could penetrate) by spraying a small amount onto a tissue then gently wiping this into the nooks and crannies with a nail brush then wiping off the excess with another tissue. I`ve had no problems since, (touch wood). Please use extreme caution when working with these panels as they are dedicated to your keyboard and therefore extremely expensive to replace. If yours has an extension lead from the LCD panel to a plug on the PCB, it should be a lot easier to clean this one cable where it enters the plug on the PCB than mine was, but still use extreme care. Best of luck, Ian

This is a know fault - Yamaha give a 2 year warranty from new so worth checking your purchase date.
The solution is to replace the whole screen assembly
The seal fails causing intermittent connection ( see photo )