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Old 03-15-2021, 03:32 PM   #1
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Default iMAC A1418 820-00431-A 8GB upgrade to 16GB

Hi. Inspired by the following iMAC A1418 upgrade:

Performed the upgrade on a working 8GB iMAC. After the upgrade and moving of the single RAMCFG jumper, the logic board is not showing LED3 and no LED4.

Logic board turns on fine with the power button and the fan does spin.

Have applied the LCD display but does not make a difference.

Q1: Is the video card (linked to LED3) requiring the use of the external LCD? Believe that LCD is mandatory for LED4 only but wish to confirm.

Q2: Is the video card RAM associated with the same 4 x LPDDR3 memory that is on the logic board? So if the LPDDR3 memory is not functional, the video card will fail (LED3 will not light up)?

There has to be a better method to confirm the installation / operation of this LPDDR3 through JTAG. Has anyone see such a solution?

Is there a clear document (schematic & boardview would be great) for the 820-00431-A chassis?

Wish to confirm the RAM strappings for the SkHYNIX 1866Mhz LPDDR3 devices for 16GB. The above youtube video is showing that a single jumper strap was moved from a 'L' to a 'H' but believe that 2 jumper straps are required to upgrade from 8GB to 16GB.

Presently, the logic board is back to the 8GB straps but using the 16GB memory chips @ 1866 Mhz.

Tomorrow will attempt to remove each chip and try again. We have a reballing kit in transit but so far, the chips have been sourced from a 100% new and original supplier we have used for years to date.
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