B250I GAMING PRO AC (MS-7A67) not booting

[thebarber]

Hi, I am trying to fix an msi motherboard B250i gaming (MS-7A67), I am a newbie but I want to learn. I have tested things and I think it is the 3VSB which is missing.

The MB doesn't boot on power button press, there is 3v on the PSIN#_R and go to Ov when pressed.

I have tested:

no shorts on ATX pin ( continuity test between GND and atx pins)
SuperIO PWRBTIN got to 3v to 0v when pressed
RSMRST is always 0v, when I follow this I saw that RSMRST from SIO is connected to R328. R328 is RSMRST <> 3VSB (0v)

Here is some measure:

3VSB = 12Kohm
5VDUAL = start @ 30Mohm but it decrease like less 20Mohm in 10 seconds (it is normal?)
5VSB_5V = 0.888Kohm
ATX_5VSB = 0.878Kohm
SYS3VSB_OFF: 5v
PCH_SBDRV: 5v
PCH_VCCDRV: 0.005v
Batlow#: 3.3v
intruder#: 2.8v
suswarn#_cp: 0.023v
susack#_cp: 0.023v
PCH_1VSB: Ov
RTCRST#: 3v
SRTCRST#: 3v
slp_sus: 0v
PCH_DPWROK: 3.42v
SIO_3VA: 3.39v / 9Khoms

PCH measure attached.

I have check some components:
U32: only pin 2 and 7 have 5v others 0v
U33 (ACPI CONTROLLER): the enable pin is 0v so no 3vsb output
Q51 (???): only 5v on pin 3 and 4

I know that I miss lots of thing, hope this could help. Can it due to a dead PCH?

Is the 5VDUAL the first voltage to fix?

[vcaina]

Re: B250I GAMING PRO AC (MS-7A67) not booting

Hi! I’m not a professional tech but I recently fixed an MSI B450M Mortar Max with as shorted 3VSB line but it was an AMD Board. Looks like this is an intel board. Do you have a boardview file for this? It’s reassuring that you didn’t get a dead short on the PCH so it gives you a slight relief. You can eliminate the PCH for now but who knows…

How I found out that I had a short in my 3VSB rail is by randomly measuring caps till I found a dead short 0ohms to groun on one of the electrolytic caps. Checked the cap on board view and found that it’s part of the 3VSB circuit, measured the other smd caps and buck converters and they are all shorted.

Injected 3V 2amps to the short and found a blown smd cap that seems to be related to USB Type C filtering which gets its power via 3VSB. The shorted cap was connected to 3VSB_RD

Maybe you could look for 3VSB_RD on a boardview and measure to see if you got a short there.

[anikin73]

Re: B250I GAMING PRO AC (MS-7A67) not booting

If pch is not sHorted then pch is fine. If not 3vsb , can u find the 3vsb producing chip to measure its voltage. Usually it is a 3 leg chip like mosfet at the lower part of motherboard..it could be any thing. Conditions not met for 3vsb to produce. Or chips that use 3vsb shorted, like pch, Ethernet chip etc.

[thebarber]

Re: B250I GAMING PRO AC (MS-7A67) not booting

Hi, thanks for your time. I have uploaded boardview and schematic if it can help. I havent find any short, attached a picture of the PCH with some measure on the first post.

Actually I think that is the SYS3VSB_OFF which are put 5vdual to ground, but I am not sur to understand where it the source of SYS3VSB_OFF.

Is there some where a picture or document which indicates the step of a boot for intel motherboard?

Thanks

https://www.badcaps.net/forum/showthread.php?t=121038

[vcaina]

Re: B250I GAMING PRO AC (MS-7A67) not booting

Hi! Can you check if Q68 Gate pin is shorted to ground or the C431 cap is shorting to ground as well? Looks like there is an AND Gate producing the 3vsb enable and a capacitor. Those are the only related components to the enable signal of 3vsb.

The mobo is not turning on at all right? It only turns on if you force jump the ps_on in the ATX connector but not when turning on via mobo Switch? If it's not turning on at all there should be something shorting out somewhere.

[thebarber]

Re: B250I GAMING PRO AC (MS-7A67) not booting

Hi! Can you check if Q68 Gate pin is shorted to ground or the C431 cap is shorting to ground as well? Looks like there is an AND Gate producing the 3vsb enable and a capacitor. Those are the only related components to the enable signal of 3vsb.

The mobo is not turning on at all right? It only turns on if you force jump the ps_on in the ATX connector but not when turning on via mobo Switch? If it's not turning on at all there should be something shorting out somewhere.

HI,

Q68 Gate => ok
C431 cap =>seems ok

If I am not wrong "3vsb enable" is from 5VDUAL (throw R549) and it is missing too.

The mobo is not turning on at all right? nothing happen

It only turns on if you force jump the ps_on in the ATX connector but not when turning on via mobo Switch? => Never tried this.

Can the PCH be dead? If yes how to be sure?