We offer used mainboard / logic board for the iMac 21.5" A1418 from 2012. The logic board setup is with:

- 2.7 i5 Quad core CPU 
- GeForce GT 640m 512mb

Details:

Apple Parts number: 820-3302
A1418 - 21.5" - 2012 - 2k lcd model

Correctly working. We also have parts for other models.