820-2850 SMC_PM_G2_EN is fluctuationing

[machelper]

Hi,

Board not turning on, when i check voltage PPBUS_G3H and all main voltage is up and down ( like PPBUS_G3H 8v ~ 12v),

SMC_PM_G2_EN is not stable (0,8v ~ 3v)

PP3V42_G3H stable 3.4v
PP3V3_S5_AVREF_SMC stable 3.3v

replaced U7000,U4900 but nothing change, only when i removed SMC_RESET_L pin all voltage is stable...

any offer for next step?

Thanks.

 

[Repairable]

SMC_RESET_L should be low. 3 v makes it think you press the button,
check u5000 area

 

[larossmann]

What is SMC_RESET_L reading with U5000 on? U4900 or U7201 is probably F'd and causing smc_pm_g2_en to fluctuate if there is no issue with U5000.

 

[machelper]

First thanks for answers.

SMC_RESET_L is 3.4V and SMC_MANUAL_RST_L is 3.1v, also replaced u7201 nothing changed..

 

[machelper]

I think my mistake is L means didnt understand. if 3.3V is SMC_RESET_L its ok ( i measured working board its shows same voltage at same pin) also Luis was published about this topic. i haveto watch it again.

So board have different problem. Maybe second SMC is same problem any suggestion ??

 

[larossmann]

_L means the signal is present when it is low in voltage.

For example, SMC_ONOFF_L, this is 3.42.v When you press the power button it goes down to 0 or 0.5v, something low, and then it thinks you're hitting the power button and the machine turns on. because you hit the ONOFF button.

is there any corrosion on this board that you can see, green or funny looking stuff?

 

[machelper]

When i checked carefully nothing seems corrosion . But some one worked on GPU before come to mydesk
What ever i think spend enough time on this board send it back....

 

[dukefawks]

I'd still check for a short on the GPU core or VRAM power bus. Could be fucked GPU after idiot did a reflow.