There is many cases on internet, most of the users pickup option to change the LCD board for a new one, someone even find the alternative (smaller size) screen. this case i will save my piano with NO COST.
My Yamaha DGX-620 has been having problem with screen display since 2011, right after 1 year warranty expired, so lucky! and the problem seems to be so typical! there are many users has same problem, the screen just shown half, sometimes worth and some time dramatically come better for a while (very soon), mostly the piano is screenless. here comes the challenge, we love the sound and we want it back to life....
first you need to take the 4 screws from the stand, then 94 more to take off! there are only 2 size of screws, quite easy but you better put them in diferent cups as shown.
1) a wireless high speed screw driver is very important, with long tips is better
2) a smaller manual screw driver for the circuit board with care.
3) a magnatic screw finder is a plus to collect every screw from it's compartment, make job smoother.
(pd: i forgot to take picture of my piano, just "borrow" some from internet, after will replace them by my own.)
Step 2: TAKE OFF THE SCREEN MODULE
the original (maybe desambled from a dead piano.....) from aliexpress sale about USD99. and if you buy a new one, does not garantee the problem gone forever, the problem is still there, the manufacture fault. Here in this case, it's all about the FLEX cable! (anisotropic conductive film) , it's quite obvious when the LCD backlight run long time, heat rise above 60 digrees, there is where the flex cable meets tacking conditions! see here for the datasheet of the cable, you will find out the tacking condition is 60 to 90 C and bonding conditions is 140-160!
so the real job is to "reflow" the flex cable to bond the sticker , this will restore the contacts.
Desamble the main board first , then the LCD board.
find a air soldering machine maybe hard for someone, but you need some thing to give you a precise air flow at 145 C, this meets the bonding condition of the flex. i bought one for this case, it's cheaper than the stupid LCD spare part and more usefull for other projects.
flow to the both sticker part for about 15 sec. then push with some force using a plastic press, repeat this job for each 2mm of distance, as the air blower covers only this range. the whole work is about 3 to 5 minutes.
(i really don't know why the pictures a up-side-down, until i find a way to edit it in instructable.com , the original pictures are fine!)
Step 4: Tricky Part of Work, Prevent for the Future!
After reblowed the flex, i decide to give some extra presure to it, since once get heat again will repeat the story, by the name of 98 screws, i drilled 2 holes to a weasted electronic board, in atatch to the original screws then cut 2 piece of ruber and push in. as shown.
Step 5: Important Thing Before Finish
put back everything is simple, important tips:
1, Set drill's torque to 1, this is due to the structure for screws are all plastic, more torque will damage the hole.
2, Be ware of speakers cables from inside of piano may cause vibrations, mine did happened once, i had to screw them again...
3, As we re-flowed the contact instead of changing them, the same problem may come back in any moment, as the room humity , gravity, built quality all thing has to do with durability. there is no grantee from anyone, but at least, you know where is the fault and can "even temporarily" correct this.