I put LGA 771 Xeon E5430 into LGA 775 motherboard GA-EP45-UD3R rev. 1.1

After easily removing by knife small pin out of the CPU socket on the motherboard so the CPU fits, it works, except maybe a problem during computer boot in case you connect USB HDD or USB flash disk as it shows error CPUID : 0001067A patch ID :0000 and not boot.
When USB drive is not connected, it works OK.

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Some maybe helpful information if you want to do the same:

If my CPU is: LGA 771 and i want to do a motherboard replace for the MB that is LGA 775, then verify MB TDP, FSB are same like CPU

1. More confidence if MB is found on the list of 775 motherboards: https://www.delidded.com/lga-771-to-775-adapter/3/

2. If CPU do not feature the adapter/reduction (when you look at its bottom - this thing is shown on above linked page), then buy it.

3. fix socket so the CPU sits well

4. if problems, duck.com them and possibly flash bios to newest version or just remove battery for a while and then in BIOS restore default BIOS settings

source tutorial: https://www.delidded.com/lga-771-to-775-adapter/