Used DELL OptiPlex 5040 SFF Motherboard T7D40 tested with I/O shield 818211801299 | eBay
DELL OptiPlex 5040 MT Motherboard R790T 0R790T
Suitable for DELL Optiplex 5040 MT Desktop Board CN 0R790T motherboard using DDR3L memory motherboard 100% tested and fully sent|Motherboards| - AliExpress
Refurbished: Dell Optiplex 5040 Small Form Factor with Core i5-6500 3.20GHz Quad Core Processor, 4GB Memory, 1TB Hard Dirve, and Windows 10 Professional - Newegg.com
Dell T7D40 Socket LGA1151 DDR3 Motherboard For OptiPlex 5040 SFF Desktop PC | Motherboards | Blackmore IT
For Dell 5040 Sff Desktop Motherboard T7d40 0t7d40 Cn-0t7d40 N5g27 0n5g27 Mainboard 100%tested Fully Work - Motherboards - AliExpress