Tectlast M40 Need help unbrick - Android Q&A, Help & Troubleshooting

Background:
I tried flashing Teclast M40Pro's firmware to the tablet in hope of it working on Teclast M40, but unfortunately bricked the tablet.
Status:
It's not totally bricked. Actually I am sure that the system booted because I can browse external storage of the tablet when I plug an USB cable to the computer. The problem is that the screen does not work (both display and touch). Now I am having problem flashing back to factory image.
What I have tried is holding power button of the tablet until it reboot and then hold the volume down button, but the tablet doesn't enter factory flash mode instead it boot normally.
More Info:
The bootloader is unlocked.
Need help:
1. How to enable developer mode without needing the screen so that I can command the tablet with adb?
2. How to boot to recovery with hardware button? This link's (https://droidrecovery.com/teclast-m40-recovery-mode/ ) method doesn't seem working. If it does work, please provide more details (Like how many seconds I need to wait and how many times I need to press the button to select the recovery mode).
3. Any other methods not mentioned above.

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I finally work out the solution.
Generally the last method mentioned by siamese007 works.
siamese007 said:
1. Open SPD flash tool for M40 and load M40 firmware.
2. click Start downloading button.
3. hold vol down + power to turn off.
4. SPD flash tool will start flashing the firmware to M40.
Click to expand...
Click to collapse
However, it's more tortuous than it seems.
The first problem I met was failing to flash back M40 firmware with error flashing _BKF_NV_LTE.
{
"lightbox_close": "Close",
"lightbox_next": "Next",
"lightbox_previous": "Previous",
"lightbox_error": "The requested content cannot be loaded. Please try again later.",
"lightbox_start_slideshow": "Start slideshow",
"lightbox_stop_slideshow": "Stop slideshow",
"lightbox_full_screen": "Full screen",
"lightbox_thumbnails": "Thumbnails",
"lightbox_download": "Download",
"lightbox_share": "Share",
"lightbox_zoom": "Zoom",
"lightbox_new_window": "New window",
"lightbox_toggle_sidebar": "Toggle sidebar"
}
I solved the problem by using ResearchDownload tool instead of UpgradeDownload tool with which I could skip flashing _BKF_NV_LTE in the settings menu.
The flashing succeeded and the system booted, but here came the second problem. The system could not recognize the IMEI and what even worse was the system would crash and reboot within a few minutes. This was reasonable as I skiped flashing _BKF_NV_LTE.
The problem was solved by flashing _BKF_NV_LTE manually with fastboot.
Code:
fastboot flash l_fixnv1 sharkl5pro_pubcp_customer_nvitem.bin

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@AnKHqz, where did you get a copy of Teclast M40 Pro firmware? Mind sharing it?

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kchung said:
where did you get a copy of Teclast M40 Pro firmware? Mind sharing it?
Click to expand...
Click to collapse
M40 Pro(M1A1)_Android11.0_EEA
M40Pro(M1A1)_Android11.0_ROW

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AnKHqz said:
Finalmente encontrei a solução.
Geralmente, o último método mencionado por siamese007 funciona.
No entanto, é mais tortuoso do que parece.
O primeiro problema que encontrei foi não conseguir fazer o flashback do firmware M40 com o erro de flashing _BKF_NV_LTE.
View attachment 5400005
Resolvi o problema usando a ferramenta ResearchDownload em vez da ferramenta UpgradeDownload, com a qual pulei a exibição de _BKF_NV_LTE no menu de configurações.
View attachment 5400009
O flashing foi bem-sucedido e o sistema inicializou, mas aí veio o segundo problema. O sistema não conseguia reconhecer o IMEI e o que é ainda pior é que o sistema travava e reiniciava em poucos minutos. Isso foi razoável, já que pulei o piscar de _BKF_NV_LTE.
O problema foi resolvido atualizando _BKF_NV_LTE manualmente com o fastboot.
[CÓDIGO] fastboot flash l_fixnv1 sharkl5pro_pubcp_customer_nvitem.bin [/ CODE]
Click to expand...
Click to collapse
Eu tenho esse problema BKF_NV_LTE
Eu não consegui resolver isso. Precisa o bootloader desbloqueado? Ou você tem um link para eu tentar. Você me ajudaria?

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1. To skip the _BKF_NV_LTE step that failed, you need to use the SPD Research Tool. Launch the tool, select the firmware and uncheck NV_LTE in the settings menu, then you should flash the fireware without error. The tool can be downloaded from https://spdflashtool.com/research-tool/spd-research-tool-r21-0-0001.
2. To make the system fully functional, you need to manually flash the file skipped in step 1. This require the bootloader to be unlocked. The unlocking method is available on https://forum.xda-developers.com/t/teclast-m40-how-to-unlock-bootloader.4185363/.

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AnKHqz said:
The flashing succeeded and the system booted, but here came the second problem. The system could not recognize the IMEI and what even worse was the system would crash and reboot within a few minutes. This was reasonable as I skiped flashing _BKF_NV_LTE.
The problem was solved by flashing _BKF_NV_LTE manually with fastboot.
Code:
fastboot flash l_fixnv1 sharkl5pro_pubcp_customer_nvitem.bin
Click to expand...
Click to collapse
Hi!I
I did the same stupid thing with the m40 pro firmware...
The first step to fix it worked, thanks!! But for the second problem, I cannot use the fastboot since my bootloader is blocked and I don't know how to unlock it, I read the guides but I don't have access to linux.
I just want the tablet to work again. Could you help me?
Thank you so much!

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fernando823 said:
Hi!I
I did the same stupid thing with the m40 pro firmware...
The first step to fix it worked, thanks!! But for the second problem, I cannot use the fastboot since my bootloader is blocked and I don't know how to unlock it, I read the guides but I don't have access to linux.
I just want the tablet to work again. Could you help me?
Thank you so much!
Click to expand...
Click to collapse
It's been a while since I unlocked my bootloader, so I don't remember the details of how to unlock the bootloader, but I would suggest trying a Linux VM or WSL.

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There is another method by Dtechflix in youtube. Download SPD_Research_Tool and run "ResearchDownload.exe".
Load the pac file (M40) -> click option button (2nd from left) -> Click "Backup" -> untick "NV_LTE" and "ProdNV" at the bottom -> Click "OK" -> Click "Update icon" (3rd from left) and proceed with the remaining steps as normal for flashing.