Late 2015 27" iMac Logic Board - multiple versions?

[pbedrosi]

I recently managed to bend the CPU socket pins during SSD/i7 upgrade to my 27" iMac. I ordered a replacement from eBay which didn't work and had additional bent pins. I order a 2nd replacement but after installing the CPU and heatsink I noticed the GPU heat sink did not completely cover the GPU memory chips.

Upon inspection I found several differences on the board - both being "late 2015 27 iMac logic Board w/2GB AMD R9 M380 GUP"

Replacement Board (not my pic but representative)

1. L-shaped GPU heat sink w/3 additional chips on the top right that are not present on the original. Underneath GPU has 3 memory chips on top and right sides.
2. Below the GPU 6 tall chips, only 4 on the original.
3. The rear of the board chips near the display connector has different chip configuration
4. PN (I think) AA00501 2NN 1624-06
   
   

Original Board (not my board, but representative)

1. Square-shaped GPU heat sink, missing 3 chips top-right of the heat sink
2. only 4 large tall chips below the heat sink vs. 6
3. The rear of the board chips near the display connector has different chip configuration
4. PN (I think) AA00501 2NN 1625-06

The last pic shows the replacement board with my original square GPU heat sink and exposed memory chips

First, does anyone know why the differences? I assume one of these was changed/upgraded or even downgraded at some point. I think the heatsink on the memory chips is ok, unlike the GPU I don't think this would cause any major heat issues. The more chips the better? LOL.

Any insight is appreciated before I decide the return the replacement board.

 

[pbedrosi]

nobody?

 

[pbedrosi]

Does anyone know if at least I can get away with this GPU heatsink coverage? I don't believe they get very hot since the undersides are not machined copper like the one over the GPU core. My original logic board seemed to have had minimal contact.

 

[pbedrosi]

nobody?

I ended up buying a new heat sink....