Both A1670 and A1671 is 2th Generation and the screen is a 2th gen screen so it will fit. The only thing that may be different enough to cause a issue between wifi model and cellular is the housing with the antennas and sim card slot causing issiues. With 12.9 2th gen the sim slot does not cause issues, can be left unplugged. Not sure about antennas but they tend to differentiate.

You can use a nand programmer p13 from JC for example and put a compatible nand in the programmer and format nand for a ipad air 3 and write/unbind wifi. Then solder Nand back on to Ipad and update firmware in dfu mode. Try to activate the device over wifi and you will not bypass activation. Remove nand from ipad and put it in nand programmer again and QueryCode//Unbind and choose fast mode. Wait untill process is done and you have the old serial wifi and bluetooth.

This is caused if the iPad has faulty soldered inductors for backlight but usually occurs when you drop the iPad or if it bumps in to something. This occours mostly at the iPad Pro 10.5 2th gen, repaired many of those.

i think most of you is over optimistic about it, the only thing that is good is that it has replaceable RAM and TB3. 64GB of RAM, should support 128 GB! Years ago the 2012 macs supported 32 GB.

If you came here and have a MacBook air with fan running it can be the following: Bad trackpad/keyboard or PO Flex/DC inboard If you have error with CPU and PCH die thermal sensor being at 128 Celcius (program: HW sensors) you have a bad/waterdmg fan, replace it. If you don't have a new fan remove the fan power it up and see if CPU and PCH Die temp is back (keep in mind to maybe turn off auto startup apps so it won't run to hot when power up without fan). If this didn't fix the problem you have problem with CPU thermal IC's or bad trace from CPU_THRMTRIP_3V3 resistor in to SMC.

Try remove the clock battery and leave it outside and have power cord disconnected for 10 sec. That solved the issue with mine, I can't have clock battery in it otherwise it won't start. And if it goes to sleep or I power it off, I have to remove power cord again for 10 sec to get it to start.