new lcd have a gray and black vertical lines

Hello. I bought on Ebay an lcd for Galaxy s3 i9305 and the lcd worked fine for an hour, then the picture was gone and the black and gray verical moving lines appeard. The touch still workes just the picture is gone. The salesman tell me that i should clean a flexcable with alcohol and leave it charging for a few hours, but i did that and still the same. I tried 3 differend motherboards to confirm that the lcd is the problem and on all 3 are the same vertical lines. Does anybody know what is here the problem. The lcd is not OEM so i probably canot expect that it will ever worked again. Thank you, Gorazd.