MI 8 bootloop/no post after display replacement


slowmail

Members
Aug 3, 2019
3
3
I broke the screen on my Mi 8 (global version), I ordered a replacement screen online, and was able to install it, but I noticed the following issues:

a) Phone would not boot with the new screen; but would boot correctly when the old screen is put back on. It simply sits at the Mi logo screen and does not post.
b) The workaround for me to boot the phone is to flash an earlier version of the rom (EU 10.3.3); but once I update to the current EU10.3.4, it will not boot at all.
c) The last version of Miui Global Rom that would boot is (V10.3.2.0 PEAMIXM); if I flash a newer version, the phone will not post, even if the bootloader is locked, and updated via fastboot or OTA.
d) The earliest version of Mi Global Rom that would boot is (V10.2.1.0.PEAMIXM); flashing an earlier version would bootloop with the new screen installed.
d) LineageOS16 bootloops
e) Official TWRP versions also can't boot, but TWRP by LR Team (from here) works.

With the replacement screen installed, Device Info Hardware shows:
LCM: dsi_ss_ea8074_notch_fhd_cmd_display
Touchscreen: fts

In all cases (no post, or bootloop), the phone would boot correctly if I swap back the previous (broken) screen.
I'm not exactly sure why replacing the broken display causes this. I was wondering if anyone here could give me a bit of advice on how to figure out what the problem might be.
 

Karpfenhai

Members
Jul 17, 2016
284
52
I broke the screen on my Mi 8 (global version), I ordered a replacement screen online, and was able to install it, but I noticed the following issues:

a) Phone would not boot with the new screen; but would boot correctly when the old screen is put back on. It simply sits at the Mi logo screen and does not post.
b) The workaround for me to boot the phone is to flash an earlier version of the rom (EU 10.3.3); but once I update to the current EU10.3.4, it will not boot at all.
c) The last version of Miui Global Rom that would boot is (V10.3.2.0 PEAMIXM); if I flash a newer version, the phone will not post, even if the bootloader is locked, and updated via fastboot or OTA.
d) The earliest version of Mi Global Rom that would boot is (V10.2.1.0.PEAMIXM); flashing an earlier version would bootloop with the new screen installed.
d) LineageOS16 bootloops
e) Official TWRP versions also can't boot, but TWRP by LR Team (from here) works.

With the replacement screen installed, Device Info Hardware shows:
LCM: dsi_ss_ea8074_notch_fhd_cmd_display
Touchscreen: fts

In all cases (no post, or bootloop), the phone would boot correctly if I swap back the previous (broken) screen.
I'm not exactly sure why replacing the broken display causes this. I was wondering if anyone here could give me a bit of advice on how to figure out what the problem might be.
Does this phone have an inscreen fingerprint reader?

If yes try to detach it on the new screen and see, if it boots.

I changed the display on my sons black shark without such issue.

Sent from my MI 8 Explorer Edition
 

slowmail

Members
Aug 3, 2019
3
3
Does this phone have an inscreen fingerprint reader?

If yes try to detach it on the new screen and see, if it boots.

I changed the display on my sons black shark without such issue.
No, my Mi 8 does not have an in-screen fingerprint reader.

It would appear there are others who have replaced a broken screen on their Mi 8 who are experiencing the same bootloop issues:

I believe the issue might be unique to the Mi 8 only, which is why you did not experience this with your son's Black Shark. I'm also not sure if it may be unique to a certain batch of replacement Mi 8 screens only, or if all of them might be affected.
 

Karpfenhai

Members
Jul 17, 2016
284
52
No, my Mi 8 does not have an in-screen fingerprint reader.

It would appear there are others who have replaced a broken screen on their Mi 8 who are experiencing the same bootloop issues:

I believe the issue might be unique to the Mi 8 only, which is why you did not experience this with your son's Black Shark. I'm also not sure if it may be unique to a certain batch of replacement Mi 8 screens only, or if all of them might be affected.
That seems really weird, the only idea left is to compare the display drivers between the rom then, maybe some working ones have either more compatible ones included or a slight different voltage setup for battery saving, I assume your replacement display may consume / need more power as the board is configured to deliver.

Just a thought, you could try to find the files or the piece of code responsible for display voltages, try to boot in a dark environment to avoid brightness increase shortly before the os finally starts.

regards

Sent from my MI 8 Explorer Edition
 

slowmail

Members
Aug 3, 2019
3
3
That seems really weird, the only idea left is to compare the display drivers between the rom then, maybe some working ones have either more compatible ones included or a slight different voltage setup for battery saving, I assume your replacement display may consume / need more power as the board is configured to deliver.

Just a thought, you could try to find the files or the piece of code responsible for display voltages, try to boot in a dark environment to avoid brightness increase shortly before the os finally starts.

regards

Sent from my MI 8 Explorer Edition
I'm confused about this response (booting in a dark environment)... it's not that the unit boots to a blank screen and is unresponsive. It simply remains at the Mi logo screen; or, in the case of a bootloop (lineageos16, and global rom before V10.2.1.0.PEAMIXM), it just keeps cycling.

Where would I find the display drivers in each rom so that I can try to compare them?

At this time, I was thinking of comparing TWRP official vs LR Teams releases; but I wasn't sure how to unpack and examine the .img file.
 

Karpfenhai

Members
Jul 17, 2016
284
52
I'm confused about this response (booting in a dark environment)... it's not that the unit boots to a blank screen and is unresponsive. It simply remains at the Mi logo screen; or, in the case of a bootloop (lineageos16, and global rom before V10.2.1.0.PEAMIXM), it just keeps cycling.

Where would I find the display drivers in each rom so that I can try to compare them?

At this time, I was thinking of comparing TWRP official vs LR Teams releases; but I wasn't sure how to unpack and examine the .img file.
You know, normally the phone adjusts its brightness right before the os comes up, therefore it might help to not increase if the display draws to much power (just a test to collect evidence for my theory) you do also know, twrp usually starts with max brightness (lr-team does not) so, i vote for voltage issue they are normally controlled by the kernel, so ask an experienced kernel developer (franco?) For some input in this regard.

Sent from my MI 8 Explorer Edition