820-01700-05 - powering on no image also on external screen

[shlom]

Hello

having a problem with 820-01700-05 from 2019 16" macbook pro

unknown history
the machine is powering on (chimes) probably to login screen (double clicking the power button activates the voice over option)..

the backlight seems to be on
but no image on display and also not on external good known hdmi connector and screen.

checked the lcd connector and board in general - looks pretty clean.

can you please give an idea where to start from?

 

[2informaticos]

Start with PRAM reset and DFU mode.

Choose first revive option.
Go for restore option, if no important data on SSD.
You can try to recover data (if needed), if is recognized in Target Disk mode.

 

[shlom]

hi
pram reset chimes but does not solve the problem

tried revive option - didn't do the trick
same for the restore option.

now the mac no longer chimes but comes on with a bright black screen, than dims and nothing more.

also pram doesnt respond now..

 

[2informaticos]

So you can complete DFU restore, but machine doesn't start macOS installation?

 

[shlom]

correct, DFU restore finishing with no error
but again, black screen (backlight is on, but no apple logo or os installation)

also, no chime or pram reset after the restore.

i tried to restore a few times, from machine with catalina and also big sur..

both same result...

 

[2informaticos]

Does it have USB activity, or external video?
Tried PRAM reset after restore?
Can you get access to its SSD in Target Disk mode?

 

[shlom]

when i connect usb mouse i get the light working on it.

nothing on external video

pram reset does not work after the restore

can't get the mac into Target disk mode...

interesting because before the restore it had pram reset and chime.
now those gone..

 

[2informaticos]

Mouse light is not confirmation for USB activity.
Read "How To collection" thread and se if there is USB activity, or really not.

Missing internal/external video at same time, can be caused by bad GPU.
But T2 restore shouldn't lose the USB and chime.

 

[shlom]

sorry about that, but can't find the "how to" section
can you please send a link?

just to make sure wheter it has or not usb activity...

 

[2informaticos]

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

 

[shlom]

hi
got a usb flash drive with a led showing activity

looks like there is activity on this mac when it's on..

 

[2informaticos]

Then GPU should be the culprit...

 

[shlom]

these boards should have cpu vcore , on the table - when only connected to charger without anything else connected?

 

[2informaticos]

Of course, but CPU core must be there, if you get USB activity.

 

[shlom]

i might be getting it wrong, because i think there is no vcore now..

which i'm pretty sure there was before (there was a chime, pram reset)
etc...

any idea why a restore would cause that?
maybe it was locked?

 

[shlom]

by locked i mean find my mac was on?

 

[2informaticos]

If locked, must give to user the option to unlock it.
So that is not the reason here.
Try repeating DFU restore few times...

 

[shlom]

checked again, for sure there is usb activity..
also, if it means anything, caps lock green light comes on and off when pressed..

will try dfu restore again..

anything that can cause the gpu not to kick in
or just the gpu itself?