Need help with password locked unknown tablet - Android Q&A, Help & Troubleshooting

Hi,
My grandfather locked his chinese tablet without knowing how.
Each time we start the tablet we arrive on an input field asking for a password we don't have.
I can't found how to reboot in recovery, however I can boot to fastboot mode with power and vol up keys.
The tablet is branded as a Kliver Klipad KL3889, but there is no other information on the vendor website (klipad DOT fr)
The user manual only says A64 Quad Core CPU and Mali 400MP GPU.
The tablet is running Android 8.1 Go edition, and shows up as "Onda (unverified)" with 1f3a:1006 id according to lsusb command.
When booted in fastboot mode, it shows up with a different id on lsusb :
1f3a:1010 Onda (unverified)
I can not reach the tablet using adb, and when I tried a fastboot
reset using the following commands :
Code:
fastboot -i 0x1f3a erase cache
fastboot -i 0x1f3a erase data
fastboot -i 0x1f3a erase userdata
all I get is the following error :
FAILED (remote: :secure mode,fastboot limited used)
Click to expand...
Click to collapse
What are my options ? Is there a way to fully reset this device ?

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perhaps web search: JTAG + tablet details. Some disassembly required. SuperUser has previously recommended Ort JTag.

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Factory reset from recovery mode

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AnierinB said:
Factory reset from recovery mode
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Click to collapse
As I previously said, I can't access recovery mode. I've tried all keys combinations I could find, and the only one working (Vol Up + power) boot into fastboot mode, not recovery mode.

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yodazz said:
As I previously said, I can't access recovery mode. I've tried all keys combinations I could find, and the only one working (Vol Up + power) boot into fastboot mode, not recovery mode.
Click to expand...
Click to collapse
Hi , try this :
1) Turn off the tablet
2) Hold "Volume +" and turn on the tablet
3) Once you see KLIPAD logo on your display, release the "ON" button (or power) while holding "Volume +"
4) You must arrive on the Android logo, and you will probably get the message "No command"
5) You can let go of "Volume +"
And that's where it becomes interesting:
6) Press "ON" (or power), and while holding the button, a pulse on "Volume +"
7) You finally arrive at the menu of restoration
You navigate through the menu by means of the volume keys, and the "ON" (or power) button acts as validation.
Choose "data / factory reset", confirm
Then "reboot system now" and you're done, if that doesn't work try the same process just with VOl- , also what you can try is :
1. Turn off your device
2. Press and hold Vol - and power button , and once you see Logo , fast release both buttons and see if you are into Recovery mode.

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Teddy Lo said:
Hi , try this :
1) Turn off the tablet
2) Hold "Volume +" and turn on the tablet
3) Once you see KLIPAD logo on your display, release the "ON" button (or power) while holding "Volume +"
4) You must arrive on the Android logo, and you will probably get the message "No command"
5) You can let go of "Volume +"
And that's where it becomes interesting:
6) Press "ON" (or power), and while holding the button, a pulse on "Volume +"
7) You finally arrive at the menu of restoration
You navigate through the menu by means of the volume keys, and the "ON" (or power) button acts as validation.
Choose "data / factory reset", confirm
Then "reboot system now" and you're done, if that doesn't work try the same process just with VOl- , also what you can try is :
1. Turn off your device
2. Press and hold Vol - and power button , and once you see Logo , fast release both buttons and see if you are into Recovery mode.
Click to expand...
Click to collapse
Thanks.
It works like you said until step 4 where I get the android logo, but no "No command" message.
Then when I hold ON button while pressing VOL+ it doesn't do anything.