RAM Support: 4 × SO-DIMM DDR4 2400MHz slots (up to 64GB). Apple iMac 27" A1419 (2017) Logic Board – 820-00609 (No CPU). Compatible Model: iMac 27" A1419 (Late 2017). Apple part number820-00609. This logic board has been professionally removed from an iMac and fully tested to verify functionality.
eBay