Macbook Pro A1989 fallen, reboots if touchbar connected

[modtool]

Hi to all,
the owner of this macbook brought it to me after a fall, that hit the upper right corner of the top case.
Luckily enough, the screen and all other parts of the machine haven't been damaged, only the touch bar wasn't lighting up anymore, and the macbook began to behave strangely, because it seems to start and work fine but suddendly it shutsdown (and at the same time the fans make a high rotation for half a second, as if an animal was annoyed by something...) at random times, sometimes after 2 minutes, sometimes after 5 minutes, but never over 10 minutes, then restarts by itself .
At first I thought that the heatspreader was damaged, so I installed an app to monitor temperatures, but that wasn't the problem, also because fans were working correctly when temperature goes high.
I disassembled the mainboard and inspected it carefully with a big magnifying lens and found no broken or fallen components, then I reassembled everything and the behaviour was the same.
Then I detached all flat cables but the display one and noticed that the mainboard and the MacOS were working good, even after 1 hour and with high temperatures (hitting 100°C during start times).
I started testing the board by connecting one flat cable at time, and starting MacOS, and everything went smooth until I connected the last one, responsible for the touch bar (the one that connects to J5100), coded 821-00681-A.
I noticed also that conneting the one that goes to J5100 and disconnecting the one that goes to J5110 let the macbook work correctly without rebooting itself, so I can say that the touchbar isn't working anymore but I didn't know that this kind of fault could led to a self shutdown.
I don't have enough experience with machines with a T2 IC onboard, but since I've seen that touchbar eeprom is connected to it, I can imagine that it's the T2 itself that forces the shutdown, but then I don't understand why it doesn't if the touchbar is completely disconnected...
Another thing that I don't understand is why in System preferences I see "Touch bar backlight" under USB->T2 section even if the touchbar is completely disconnected...
In the end, I need an advice to understand if the touch bar can be replace with a new one without the T2 going upset and screw something, because I've read that putting the mainboard in another topcase may led the T2 to lock the platform and disable access to the onboard ssd, as also have read that a not-working touch bar may cause problems on future firmware/MacOS updates.

Please, can someone enlight me about these questions?
Thanks

[Stephen]

Re: Macbook Pro A1989 fallen, reboots if touchbar connected

Heads up, any model with Touch Bar will have issues if the Touch Bar goes bad. You will need to replace the Touch Bar even if it is not cracked. You will have booting issues or functional issues if the Touch Bar goes bad. A1706, A1707, A1989, etc. all have these known issues. I would suggest using a used top case if you have one laying around with a good Touch Bar and testing it in that. This will easily tell you if the issue persists. Hope this helps.

You can replace the Touch Bar on these models without issue, they are not married to the board, the only thing married to the board on these models is the Touch ID. Just make sure you get the correct Touch Bar for this model.

[modtool]

Re: Macbook Pro A1989 fallen, reboots if touchbar connected

Hi Stephen,
thank you for the hints, a new touch bar arrived, I installed it and everything has gone well, no more reboots and who knows what other problems it could have caused in future MacOS updates.
Have a nice day

[Stephen]

Pleasure to have helped you!