I recently got 2 basically spotless C64's in their boxes to add to my collection. Inside they are clean as new and neither of them look as they were used much. The issue I have is both of them exhibit a black screen upon boot up. I have read that the most likely cause is a dead PLA chip seeing as they are getting power and the internal fuse checks out. I have read that since I do not have a dead test cart that if I were to plug in specific titles of cart games they might work as the games don't require some of the PLA functions to operate. Has anyone heard of this and if so it is a reliable test? Starting with the easiest forms of diagnosis would be the best method in my opinion and if I can avoid it I would rather avoid buying a dead test cart for the time being. Otherwise I will just set these aside and mess with them later after I have purchased the correct diagnostic tools.