A MacBook came in over the weekend showing graphic anomalies on the screen almost immediately after pressing the power button. Horizontal lines are easy to diagnose: graphics processor failure. Vertical lines are easy, too: failure of the panel itself. But the patterns on the screen could be any number of things, from the panel itself, to the low voltage display cable, to the graphics processor, to software. I ordered up a main logic board.
By assuming failure of some part of the graphics processing system, I went ahead and ordered a main logic board. After installing it, and noticing the same exact problem, I reconsidered my diagnosis. What are the odds that the same exact pattern would appear from two graphics processors suffering the exact same failure?
After scratching my head for a while, I stepped back and went to Apple’s MacBook service manual. There are great step by step troubleshooting guides for every conceivable issue, and while I like to think I have them all memorized, in this case I messed up.
Remembering that the main system RAM is shared with the graphics processor, I pulled one of the chips from the user-accessible slot. Problem solved. Since the RAM was from us and covered by our lifetime warranty, parts and labor were covered. I only wish I thought of this before keeping the customer’s machine longer than I had to!