skylogger wrote: Do you think this first rail should be active, even with the communicatitions connector not plugged in (box still on bench not in car)
It looks to me like the power is coming through the comms connector. The mains conditioning seems to be for the two terminals that go to the charger board. So that would be a provisional "probably no".
In your previous message, you say what the voltages should be for all the supplies that get created from this first rail, but I did not see where you mentioned what this first rail voltage actually should be.
Nearly half of the top of the top board seems to be devoted to a power supply; there are a lot of inductors, electrolytic capacitors, and power semiconductors underneath.
I see at least two capacitors with the "V" voltage code (220V and 330V). These are too small to be 220 volts and certainly not 330 volts.
From https://forum.digikey.com/t/smt-electro ... rating/974
[ Edit: so these would be 220 μF and 330 μF, both at 35 V. Other capacitors there are rated at 470 μF and 10 V. ]
A 35 V rating suggests 24 V nominal design voltage. The next lowest code is E for 25 V, too close for comfort. The battery voltage, nominally 12 V, is a little low for sending over thin wires, and besides it varies from 11 to 14.4 V depending on the state of charge of the battery, and the loads.
[ Edit: besides, a lot of industrial gear seems to like 24 V. ]
[ Edit: so what I'm trying to say is, I suspect that there will be a regulated 24 V sent from the top board to the charger board. ]
I am thinking that the main rail coming across the flex cable will probably be dead until 12v is supplied to pins 2 and 7 and ground connected to pin 10 of E-02.
Yes, that seems to be the case.
I also connected my old half dead 50 year old oscilloscope in dual chanel diff mode to see what is across pin 11 and 12. attached is what I see, but its probably just noise from the fluro lights i'm working under. looks like 4vp-p
Difficult to tell, but not even 4 V peak to peak is certainly too low.[ Edit: had capacitor values wrong. ]