MacBook Pro A2141 Green or purple vertical bars on display repair

Problem description
Possible Diagnoses for Green or Purple Vertical bars on the display

Symptoms

 * Vertical lines on the screen

Solution
The most important diagnostic test to perform, is checking to see if the machine properly displays an image on a KNOWN GOOD display. If the vertical bars are still present on a known good display, the issue is likely related to the GPU or VRAM.

Unfortunately, there is no definitive way to determine a VRAM fault from a GPU fault, especially since when this issue is present, the board usually will not boot into an OS. You can try heating the GPU at 100C for 3-5 min to see if the issue will temporarily resolve, if it does, the GPU is the cause of the issue. It is important to note that heating a flip chip at a low temperature for diagnostic purposes is not a solution, and will not "fix" the problem. Higher temperatures should not be used, as they can negatively affect the life of the chipset if it is not the problem. If no change in the problem is seen, the VRAM may be the issue.

If the GPU is the issue, you can reball one from a donor board as long as the proper tools are used. You should be using a BGA station, and you should not exceed 260C during the removal or replacement of the chip. Use 63/37 solder to reball the new chip. DO NOT REBALL THE OLD CHIP. THIS WILL NOT SOLVE THE PROBLEM. If the VRAM is the issue, replace all VRAM chips at the same time.