This iPhone X was completely dead, no sign of life at all. However when I plugged a power supply into the battery port it immediately started drawing maximum current. This occurs because one of the main power supplies that are on even before booting is shorted to ground. In this case it was vdd_main.
The X, XS, and 11 all have motherboards which are a sandwich of two boards with an interposer in between connecting them together. A carefully calibrated heater allows separation of the two boards without melting any of the solder on the two boards.
The short was located in a classic way on the top board using a cold spray and then driving power into the shorted signal. Whatever gets hot, melts the frost! In this case it was a capacitor next to the CPU, very common in the X
After that, its just remove the capacitor and put the two boards back together.