P5VG3S_PGOOD need to be returned to u7800 if u7800 doesn't get that signal it will cat off P5VG3S_EN ,it's normal ,what you need to do is to check for the none working of your touch bar .
ok, but for turning on the motherboard I should connect the power button and the battery, right?
This is look like my motherboard for the moment, it is connected just to the USB C connector, nothing else.
If the keyboard connector has some oxidation it can make your motherboard turn off , you should found the right pin on the keyboard connector which can power on your motherboard and fan should be in use to see if it will spin .
So I cleaned up the keyboard connector and after that I connect the keyboard to the logic board and what I notice when I connect the USB type C to the motherboard the fan start to spinning but for a little while, and after the fans stops. Yo can see better in the video attached
Check if DFR_PWR_EN On C5105 PIN 1 Does it come in a short of time or not .
the touch bar seem not good or the connectors it self is not pointed like it should be or some line is been ripped .
You will need to power on the motherboard without keyboard .
So your advice it will to connect all the peripherical, without the keyboard, and try to start it, see if will work, right?
what is the reason that you think the touch bar is broken?
Try to work with the motherboard and fan nothing else , no keyboard no screen .
The fan is included in the keyboard connector, if I will not connect the keyboard to the logic board, the fans will not spin, am I right?
ok work on it without fan and you have to know how to power it without keyboard than check if the voltages dropped or net .
