820-00875 not booting

[semaca]

Hello,
So this board is not booting.I have on the Amp meter 20v and 540mA,after 10 sec it's dropping to 420mA and after another 30 sec to 380mA and stays there .
All important power rails are present .On L7210 and L7220 I have 0,9v.On the schematics say it should be 1,8v.If the battery its plug in its charging fine.
For the backlight circuit to work does the screen need to be plug in? I'm asking this because on U8400 EDP_BKLT_EN is 0v .
I didn't spot no corrosion no shorts .
If somebody can point me in the right direction I'll be more then grateful .
Thank's.

[mon2]

Re: 820-00875 not booting

For the backlight circuit to work does the screen need to be plug in

Yes.

What is the voltage of PPBUS_G3H ? (Measure at each side of fuse F7000)

[semaca]

Re: 820-00875 not booting

Thank's for reply .On both sides is 13,06v

[mon2]

Re: 820-00875 not booting

What are the voltage readings for the following ?

SMBUS_BATT_SCL
SMBUS_BATT_SDA

ALL_SYS_PWRGD

See attached and monitor the order of the power path flow of the A1708.

More can be posted if the above checks are ok.

[semaca]

Re: 820-00875 not booting

Thank you . It will take me some time to measure all that, so Ill let you know when I'll finish.
Here the fastest ones :
SMBUS_BATT_SCL 3,4v
SMBUS_BATT_SDA 3,4v
ALL_SYS_PWRGD 3,2v

[semaca]

Re: 820-00875 not booting

I got all the measurement .See attachment. My conclusion is that is something with the cpu, unfortunately .What do you think ? Thank's for your time.

[semaca]

Re: 820-00875 not booting

Hi,
So it was missing CPU_ZVM_L witch was coming from CPU or PCH.Everything els was present.Clearly ,to me, CPU damage. So I decide to apply the "miracle" remedy, heating up the cpu.I heat it up for about 7 min at 230 Celsius and ,to my surprise, it worked .It booted up .I'm sure its not going to last but at least I can recuperate the data from the ssd.
I want to thank you very much for those diagrams you send me.They are great to diagnose a faulty MacBook.
Semaca

[mon2]

Re: 820-00875 not booting

Very nice! Glad to hear they helped. TBH, about to remove and replace a large BGA CPU soon with our workstation. The vendor (Seamark) claims to is a painless project.

[semaca]

Re: 820-00875 not booting

How did it went with the cpu replacement? I check them site, they are not chip...