MacBook Pro A1990 Not turning on, drawing 0.00A - 0.02A at 20V repair

Problem description
A1990 MacBook not turning on, drawing 0.00A - 0.02A at 20V, PP3V3_G3H_SOCPMU present, but PPVCCPRIMCORE_PRIM_REG and therefore PP3V3_S5 missing.

Symptoms

 * Not powering on
 * Missing PP3V3_S5 and PPVCCPRIMCORE_PRIM_REG voltages
 * Only drawing 0.00A - 0.02A at 20V as measured by USB-C meter

Solution
Do not replace U7800. Instead, put device into DFU mode and select advanced -> repair. Read this apple article.

The problem seems to be T2 not talking to the PMU correctly. Note, you need a battery connected for PMU to work. Best to completely assemble the device.

The 2019 16" model has the same issue.