820-00165-A Fan Spins for sometimes, goes off and spins again. But not turning on.

[Saurabh]

There was a corroded capacitor C1902 near the U1900, replaced.
2 registers near SMC replaced
No sign of any other visible damage.

Stage 1: The fan is spinning and it shows 430mA on the power supply. All voltages are present and the CPU is also getting warm.
Stage 2: It goes off and comes to 85mA.

Keeps cycling back between these 2 stages.

Things I have tried
- Replaced U1900, no go
- Replaced SPI ROM/BIOS from another 820-00165-A MLB, no go.
- Reflow SMC, no go

Please help me with the next steps.

 

[2informaticos]

First of all, welcome to the forum!

ALWAYS reball SMC, when you detect corrosion near SMC.

 

[Saurabh]

Thanks @2informaticos.

Does the symptoms indicate SMC issue?
There was not much corrosion near SMC. Checked from all sides under microscope looks clean.
I just reflowed it.

 

[2informaticos]

SMC is very sensitive to accumulated crap underneath.
This create leakage between its balls.
You should discard such problem first.

 

[Saurabh]

I installed the same SMC after reball, didn't work. Installed a new SMC didn't work.
Does SMC need any kind of programming?
Should I use one from a donor board?

 

[2informaticos]

Of course, always from donor board, same model.

You should have other problem, if original reballed doesn't work.
Which is the actual symptom of your board?

 

[Saurabh]

With a donor SMC, the device is back to almost the initial stage.

Fan spinning continuously but the current drawn keeps cycling between 2mA - 405mA.

What should I check next?

 

[2informaticos]

Check all SPI Bus Termination resistors and their traces; with patience, there are 20 approx.
Clean/remove J6100.

PLT_RESET_L goes high?

 

[Saurabh]

J6100 - absolutely clean.
SPI Bus Termination resistors - Values are fine
PLT_RESET_L - Fluctuating between 3.36 and 0.09

 

[2informaticos]

Does it stay on in SMC bypass mode?

 

[Saurabh]

Yes, the MLB doesn't go off after the SMC Bypass.

Without SMC bypass it keeps restarting.

 

[2informaticos]

Then should be a problem with a SMC sensor.

Board just stays on in SMC bypass, or even works?
Check for USB activity at least.

 

[Saurabh]

After the bypass, the device doesn't work. Only the USB is active.

SMC sensor switch looks clean. PP3V3_S4SW_SNS is 3.3v and goes up and down with the rest.

What next?

 

[2informaticos]

SMC sensor???
It has more than 10 sensors...

"Only the USB is active"
Do you get USB activity, or only power?
Read how to check USB activity:

HOW TO collection

I hope this "How to" collection will help our members. I will possibly modify this post in time, if updates available. Trigger SMC_ONOFF_L (PMU_ONOFF_L): It reffers to simulate power button function, when the keyboard is not connected. We need to do this when we work with the board...

boards.rossmanngroup.com

 

[Saurabh]

Checked, the USB indicator doesn't blink. It stays always on.

 

[2informaticos]

PLT_RESET_L stays high in SMC bypass?

 

[Saurabh]

Yes, it stays at 3.36v in the SMC bypass mode.

 

[2informaticos]

To be sure, check for external video.
If not present, try known good BIOS.

I still suspect some area affected by corrosion.

 

[Saurabh]

Tried 2-3 good BIOS from donor MLBs, no go.

 

[2informaticos]

Heat CPU (especially PCH area) with quality flux.
Do not apply more than 180-200 degrees, for 15-20s; no need to melt the balls, only burn accumulated crap underneath (if exist).
BTW, I talk about board temperature, hot air station need higher setting.