Do these backplanes, power distribution boards and cables belong together? like coming from the same system but just missing the motherboard?
what i see it his:
- PSU is 12V only
- Power distribution board does not seem to haven any chokes/vrms…so 12V only as well?
- Backplane seems to have chokes, which could mean the 12v to 5v stepdown should be happening there.
but my knowledge of electronics is not good enough to positively identify that.
If the cables belongs to the backplane, I would say it provides only 12V +ground and grey is probably some sort of sensing wire. Since there is no other power connector, this again would point to the 5V coming from the backplane itself.
The only other option is that that little connector next to the main power, needs to get 5V from the MB?
(Color coding in server parts, while not entirely reliable, is usually solid. Black is ground, yellow is 12V, red is 5V)
3.3 volt is usually not needed to power sata/sas drives. So unless the board uses it, you don’t need it.
My best guess here is that either:
- some sort of signal is missing that tells the backplane to turn on properly. And this might be the 3.3V you are talking about
- 5V power should come from the MB with an extra power cable
If you find out where to supply 5v (or 3.3) you can use buck converters for 12v to 5v, like the ones I used here: