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Mac Book Pro Unibody 2012 A1286 macOS Sierra Mac Book Pro 2012 Unibody macOS Sierra- screen starts flashing>horizontal banding then shuts off. Researched and found out one of the RAM slots is bad (not card issue). Removed RAM from defective slot. Now MB Pro is running fine, but with a single 8GB instead of two 8GB R AM (16GB total). I read that this is not uncommon for this model and is a motherboard issue. How can I fix this?
I’ve had success both tightening the bracket screws and loosening them. Also try a 4 GB stick in the slot, sometimes a slot will take a lessor stick.
Check the Apple serial number sticker on top of the ram contacts. It’s a layered foil sticker and on mine the sticker seemed to have shifted or degraded so that the foil was shorting the edge contacts for the bottom ram slot. I removed the sticker and placed a new layer of kapton tape in between it and the contacts and the problem was solved.
