Best place to get high-current 5V on mobo?

[flyingfishfinger]

Hi,
As part of the "Under $500" X61 project, people may have noticed that I bricked a motherboard with the overvolting mod.
I picked up another, but to be safe and eliminate potential causes of failure, I wanted to make sure I tap 5V for all my additions in safe places. I was using the HDD connector as well as the little edge-connector next to the WiFi switch (what's that for, anyway?), but I wanted to see if there is a better place to draw lots of power from. Things I want to / have been driving:
- USB 3 card
- HDMI adapter
- M500 SSD

The schematic shows several 5V rails, and I haven't had time time to dig into that too much. Does anyone have a good idea what the best place is?
Thanks!

R

[rkawakami]

I would say that VCC5M is the main one to tap. It comes out from the MAX17003 power supply controller. It looks like it can supply up to 7A of power. Given that amount of available power, I would protect whatever you are trying to power with an inline (axial) fuse. Littelfuse makes several styles and can be bought from DigiKey or Mouser.

edit: As for the edge connector... I believe that is designated U38. It apparently is for debugging the board at the factory or field service. It taps into one of the system data buses, as well as the VCC5B supply. Tracing back, that 5V comes from a DC-DC controller labelled BD4176KVT which I can't find any info on besides it seems to be made by Rohm. I don't think it is meant to drive any high-current which may explain why your old motherboard has gone to Silicon Heaven.

[flyingfishfinger]

Thanks! I could definitely have found that myself...sorry.
What's strange though is that it worked fine with all the things attached to the edge connector until I did the CPU overvolting and tried stresstesting it. That's how it died, as far as I can tell...why that should affect that connector I have no clue. I can do some digging when I get home from work..

R

[flyingfishfinger]

....VCC5B supply. Tracing back, that 5V comes from a DC-DC controller labelled BD4176KVT which I can't find any info on besides it seems to be made by Rohm. I don't think it is meant to drive any high-current

.

As far as I can tell, VCC5B powers the main SATA connector (HDD) as well as 5V on the VGA port and both fans, many of these are fused with resettable PolySwitches.
As for the regulator you mention, I don't think it sources VCC5B; it switches it via transistor Q59 (a 6A N-channel Farnell part) and signal VCC5B_DRV directly from VCC5M.

3.3V are obtained the same way; VCC3B is switched from VCC3M via Q77 and signal VCC3B_DRV. Also, VCC3B is used for several things and fused in a bunch of places too.

So I guess the answer is that VCC3B and VCC5B are decent high-current sources, and indeed they are available in many more places than the "M" lines.

I hope this helps other folks as well!

R