MacBook Air Early 2020
To open the Mac you need a PL4 Pentalobe screwdriver.
The motherboard number is on the top (easy to reach) side of the board right beneath the CPU, but professionally hidden by Apple under the heat sink.
This a Mac with T2 chip.
The ROM is a WSON 3x4 chip (32Mbit 1.8v).
Plug this in every time you work on this Mac.
it will show you if the CPU/PCH is running (Green LED) even without booting into an OS, The two Red LEDs show if the Mac is on and if the 5volt line is correct. It will also warn you if the VBUS is much more than 5 volts by blinking the 5volt LED. LINK
This little board works as a 'Known Good' battery. It makes it easy to see if the SMC and the ISL charging chip are working.
It also allows you to test the Mac using a power supply through the battery port. This way you can test the Mac even when the charging circuit is bad.