newbie questions

[cloghin]

Apologies if I am asking the wrong questions , but not sure how else to start:

I have an A2251 / 820-01949 Mac book pro with no power, 20 v on USBC meter and 0.05 Amps. Following this link ( below)

* Do I need to remove the board from case so I can access its other side ? The link calls for measuring PP3v3_S5 ( I suppose this is in diode mode with positive probe on ground) , but I don't know how to do that without removing the board from case.
* I have the FlexBV board , are the values displayed in volts diode mode only ? Because my etekcity multimeter shows values in millivolts perhaps ( 300-500) ?
* If I find the busted part, what tools I need to replace it and where do I get the part ? Can I send the board to a repair shop ?

Thanks,
Colin

[mon2]

What is the history of the unit? Any liquid damage?

20v is a good start since this confirms that the power delivery controllers are working to dial up the required voltage.

If no liquid damage, consider to start with a DFU firmware attempt using another known good macbook. You do not need to open up the unit for this process. In the US - 2 good shops for service, if required are Louis Rossmann - believe he moved out to Texas. Other is Alex @ NorthridgeFix repair - California. Both have tons of YT videos.

Tim:

Apple MacBook Data Recovery Services | TCRS Circuit

[cloghin]

No liquid damage , it just stopped working after keeping the laptop in the car hidden under the floor mat for a hot afternoon . I tried the DFU route and it does not enter DFU mode , it reads as Apple controller and an attempt to revive stops midway probably when trying to run the firmware. I would rather learn something in the process rather than send the unit to Rossmann, so if I need to take the board out I will. I already replaced the battery blindly thinking that it was the failed component.

[mon2]

Carefully, measure the voltage to ground of F7000 (check both sides). We are checking the voltage to ground of PPBUS_G3H.

[cloghin]

Both sides of F7000 measure 12.66 V to ground. That is PPBUS_G3H and PPVBAT_G3H_CHGR_REG. Diode mode is 272 on both sides.

[mon2]

This is a good voltage for PPBUS_G3H to run the logic board.

Locate the debug led which are probably not stuffed but you can use the PCB pads to measure the PP3V3_S5 voltage to ground without removing of the logic board.

[cloghin]

very small PCB pad , but no voltage drop on PP3V3_S5 . Is there is a LED on the other side of the board ? So with a short on this circuit, it is more difficult to identify the source or should I remove the board ?
I don't have a thermal camera

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance to ground of the same pad you tested for the voltage. One meter probe on the pad; other meter probe to ground (metal shield is ok). Color of the meter probes does not matter for a resistance check.

[cloghin]

61K resistance , very high

[mon2]

Good. So next need to find the enable pin for this rail. This will be the EN pin. What is the voltage to ground of the EN pin for this missing power rail? That is, if the part is being turned on but fails to supply the power rail then the regulator is defective.

[cloghin]

I am not sure how to find the enable pin EN . The pdf or .brd file does not lead me to one. In the picture below, the 'enabled by' text does not contain what enables it. Also, the battery is disconnected. Not sure how to proceed with my limited knowledge.