Yamaha dx27 black squares on falf screen HELP

I’ve seen a yamaha DX 27 on sale for 70 dlls
But it doesn’t work, only shows black squares in left half on the screen, and that’s it.
It does not come sound when they press a key
The seller says it has been open
And he had tried to repair it, but he couldn’t.
I don’t know if the problem can be the internal battery
That’s my thought
Anyway, I hope to get an answer quick

Almost certainly not the battery. In most keyboards, the battery’s only function is to retain program data when the keyboard is powered off. It has nothing to do with the actual operation and functioning of the keyboard.

That said, if the battery is dead and the keyboard loses all of its internal programs, some synths (the DX7 is a notable example) will look like they are dead in the water until you load in good data. (Most synths, on the other hand, simply revert back to factory default programs when the battery dies, and they play just fine.) But when this happens on the DX7, the screen displays jibberish, not black squares. This sounds like a more significant problem, likely one not easily diagnosed from afar.

Oh well…
I think I should find another one in better condition
The last thing I want is lose money
I think I’m not gonna buy that
Thank you for your reply

Although this thread is long dead; one important note:
The Battery IS the culprit in most cases here. It works as follows:
The Battery retains the onboard sound “RAM” Chip.
As soon as the Battery looses capacity the RAM is lost and the DX7s processor, dumb as he is, interprets the now empty RAM as Sounds (given the specific structure of how the data is stored on such Memorys) giving out this all gibberish Text and, obviously, playing nothing or highly random notes if ever.
I think its always worth buying such a Unit and slapping a new battery in, if the price is reasonable.

Ah ja, and specific instructions of replacing the battery and reuploading the sounds via MIDI! (yuuuup thats the way) are to be found online, but its a bit tricky concerning the menu especially with the DX7 IID Models.

kind regards