LCD Panel Display problem in XY-213 Digital Musical Keyboard

Hi Everyone,
Its been like more than 3 years I'ven't been logging into the forum. I'm really sorry not to signing in often. Anyways now I finally logged in to put a question on electronic musical instrument like the digital keyboard from Xin Yun and the model no. is XY-213 54 keys keyboard.
Well it was good when i played it for long. But when I used the battery with required supply of voltage with AA batteries, I got the LCD panel dimming out often. And with time the display on the panel completely went off that you can't notice anything on it other than its engraved inside ones and the glowing of backlight LED . So I've opened the screws inside and checked whether the connections were lose. But they are all intact. I even resoldered every pins under the PCB. But it didn't help. So I wonder the LCD panel is not properly pressed or something, opened the LCD board and cleaned out the carbon contacts. I found it has pins like RD, CS, WR, DATA, VSS, VDD, +, and 2 other pins for LED terminals. Well it didn't help even after pressing the LCD screen properly. Nothing was displaying on the screen. Hence I tried to find the datasheet of that LCD which is HT1622-v2. I thought v2 means version 2 but I could only get the datasheet for just HT1622 which mentioned the max supply voltage that can be provided to LCD is 5.25V. Therefore I measured the supply voltage to the LCD in the when I turned ON the keyboard found to be 6.29V. For seconds, I thought wow it must be the culprit that might have been preventing LCD not to display any visible data. So my question is... Is the LCD really dead due to the high voltage supplied in it? And is there any way to repair it without changing to new one. And how would i check that LCD is really dead or not? I've attached some pictures of it like when i press slightly the data get displayed. So guys recommend me how to find the fault in the PCB/components.