There are many cases on the internet, most of the user's pickup option to change the LCD board for a new one, someone even finds the alternative (smaller size) screen. this case i will save my piano with NO COST.
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My Yamaha DGX-620 has been having problem with screen display since 2011, right after the 1-year warranty expired, so lucky! and the problem seems to be so typical! there are many users has the same problem, the screen just showed 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 is only 2 size of screws, quite easy but you better put them in different cups as shown.
1) a wireless high-speed screwdriver is very important, with long tips is better
2) a smaller manual screw driver for the circuit board with care.
3) a magnetic screw finder is a plus to collect every screw from its a compartment, make the job smoother.
(PD: I forgot to take pictures of my piano, just "borrow" some from the internet, after will replace them on 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 guarantee the problem gone forever, the problem is still there, the manufacturing fault. Here, in this case, it's all about the FLEX cable! (anisotropic conductive film) , it's quite obvious when the LCD backlight runs a 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 140-180C
so the real job is to "reflow" the flex cable to bond the sticker , this will restore the contacts.
Take off the main board first, then the LCD board.
find an air soldering machine may be hard for someone, but you need something to give you a precise airflow at 170C (This temperature has been edited, as the 1st time i used 145C it last only 1 month), 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 useful 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 an 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 reflowed the flex, I decide to give some extra pressure to it, since once get heat again will repeat the story, by the name of 98 screws, I drilled 2 holes to a wasted electronic board, in attach to the original screws then cut 2 pieces of rubber 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, Beware of speakers cables from inside of piano may cause vibrations, mine did happen 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 humidity, 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.