Macbook A1708 820-00840-A / 20V 400ma / No Post

[GfilipeZ]

Hi,

This machine stopped working suddenly.
Like a wrote in the title, the amperage goes to 650mA and after a few seconds drops to 400mA. CPU and SSD warm a little, but nothing special.
Apparently, sound alike the Logic Board is going to boot normally. But there's no image on display; no image on external display; no backlight on display neither keyboard and no green light on "caps lock". Only trackpad clicking.

I already checked on microscope for corrosion signs, and there's no liquid damage. There's no sign of previous intervention on Logic Board or damage in any components.

Checked all voltages of page 69 (Power Aliases), and all voltages are present. The only voltages that caught my attention were the PPVCCCPU_S0G_PH1 and PPVCCCPU_S0G_PH2. Both goes up to 0.9V, but if i'm right on a normal boot the voltage should drop to 0.6V, wright?

 

[2informaticos]

Do you get CPU core voltage (L7210)?
Check it after 10-15 seconds.

 

[GfilipeZ]

Yes, stable 0.953V

 

[2informaticos]

Not good, CPU core shpuld drop (as above mentioned), when board really boots.
Test the board alone on the desk; only charger connected.

PLT_RESET_L goes high?
You can try known good BIOS.

 

[GfilipeZ]

Yes, i'm working on the desk only with the board and power supply.

I forgot to mention, that i already tried a known good bios file and IC.

PLT_RESET_L = 3.3V stable

 

[2informaticos]

Heat CPU with quality flux.
There may be accumulated crap underneath.

 

[GfilipeZ]

Any tips of how much heat and how much time?

 

[2informaticos]

You don't need to melt the balls; just burn eventually crap.
180-200 degreees C, for 15-20s should be good enough.

 

[GfilipeZ]

Already tried it, but still with the same behavior.

I'm not gona loose more time with this board.

Thanks 2informaticos!