820-4924 no image, no CPU fan

[onetailbeast]

Hi,
I?ll be as brief as possible. (I am beginner)

820-4924 (macbook pro early 2015)
Problem ? no image. There was an image for a split second when opened the Lid ? then black. Restarting, pulling battery ? doesn?t help. Later tried to shine flashlight through the Logo, but was too late. By ?late? I mean after disconnecting battery 3-4 times (with nylon opening tool) now on Start laptop Chimes, cuts off Chime in the middle, restarts, Chimes, cuts off chime in the middle, restarts, Chimes, cuts off? loop.
Remembered have Same laptop with broken LCD. Great. Swap motherboard. Did. Laptop worked for a while until I connected battery ? now second board has same issue. Suspect battery-killer, but still need to fix (now two) boards. Now will use battery from second machine.
Also CPU fan doesn?t spin anymore.

Have heard Louis mentioned PPBUS_G3H in his videos like a gozillion times so got multimeter.
PPBUS_G3H ? 12.4V (15.84 kOhm line resistance)
PP3V3_S0 ? 3.3V

Please help to figure out.

 

[2informaticos]

Post exact voltage for SCL/SDA lines of battery bus; just charger, do NOT connect that battery again.
Also post diode mode (red probe to ground) on same lines.

12.4V is strange value for PPBUS_G3H; check with other multimeter, we need to confirm real value.

Fan doesn't spin on the start as normal behaviour for this model.

 

[onetailbeast]

SCL/SDA I've measured through R5380/R5381 - 3.42V diod mode - 0.340 (red on Ground)
PPBUS_G3H from several places on motherboard still 12.4V on one multimeter and 12.6V on another in diod mode - 0.151

 

[2informaticos]

OK, 12.6V sounds good.
Stop using the other multimeter for voltage; use it for diode mode and ohm scale.

Battery bus doesn't look affected.
But is still possible that SMC got damaged.
Clean the battery connector as best as possible.
Better to remove it and inspect for liquid sign under it.

At least one board is half-dead now.
Connect charger and battery, post SCL/SDA voltages.

Be aware, never connect/disconnect battery when charger is plugged in.

 

[onetailbeast]

with battery and charger plugged in - voltage on SCL/SDA is same - 3.42V / 3.41V

 

[2informaticos]

Seems that there is nothing wrong with battery.
At least doesn't generate overvoltage on its bus.
But connect/disconnect it several times, could affect SMC...

Machine still restart if starts in SMC bypass mode?
PRAM reset done?

 

[arnonabuurs]

I just got one with the same issue. Note that the fan does not spin, only after a temperature treshhold is reached. Try change display cable, they always fail for this model. Did the trick for me just now. 50% of all display issues with 4924 are display cable. Easy to swap and test. Many people replace the display while it is only the cable, did that for 2 years so I have a nice stock of working displays now

 

[2informaticos]

MLB supposed to be checked on the desk alone, without LCD connected.
If doesn't restart, then LCD issue; or other accessories issue.

 

[onetailbeast]

You might not remember beginning of the thread (as you help more then just me). There are two identical macbooks. Problem started in #1. #2 I just happen to have with broken screen. So after testing lines (with your help) I suspect the culprit to be battery #1 (which you told me NOT to connect any more) so I am testing macbook #1 with battery #2. So far it is working. Tomorrow will play a non stop movies on youtube to see if macbook survives with charger plugged in and without.
Thank you very much for your help. Hope to have new questions for you soon.
Say Hi to Louis please.

 

[onetailbeast]

arnonabuurs - thank you for the tip. Noted.