[Samsung Galaxy Tab S4 Questions & Answers] BassFuzz:
Hello,

I put myself in quite a pickle trying to install magisk on my SM T835:

- OEM unlock toggled on, factory reset, enabled usb debugging.

- Downloaded the firmware manually via bifrost since frija couldn't pick up the device when connected.

- Patched AP file with magisk and tried flashing it with Odin.

Initially I couldn't get the tablet to connect with Odin, it would be "Added!!" but would always fail at "setup connection".

Tried different cables, usb ports, nada.

Tried a different pc running win11, nada.

Somebody mentioned it working only on win7 and lo and behold, it did:

- I selected the patched AP file and flashed it (the AP file alone, which I think might have been the problem), it finished the job without any error.

The tablet booted back to its usual splash screen but with an open lock and "Custom" written under it.

This is the bootloop.

I panicked and tried wiping the cache partition and factory resetting (which is probably really bad as it may have deleted the usb debugging authorization).

Different key combos now do the following:

- Vol+ Vol- Power: turns on, bootloops;

- Vol+ Power: turns on, recovery mode;

- Vol- Power: turns on, recovery mode;

- Vol+ Vol- connect via usb: displays the charging logo (cirlce with lightning bolt) with no percentage, a minute later turns off and starts bootlooping.

Before entering recovery mode the screen rapidly flashes a blue screen with "installing system update" and immediately after "no connection", only then it goes into recovery mode.

The only way of putting the device in download mode is via "Reboot to bootloader" from recovery or by a split second timing of Vol+ Vol- Power and connecting via usb and releasing power as soon as the device vibrates.

The two download modes differ as the first one (reboot to bootloader) only shows the DL mode screen itself while the second, trickier one, shows a bunch of data on the upper left quadrant (RPMB fuse blown, RPMB provisioned, CURRENT BINARY, FRP LOCK, etc).

Here is why I believe the three samsung technicians told me to replace the motherboard (after having quoted me 30€ to restore the OS): the device won't connect via usb.

It does accept charge, that I've tested, but it won't be discovered as a device by windows.

Odin can't see it, adb devices reports a blank list.

I tried all the different versions of Odin (modded and stock) from that one post here on XDA, nada.

I tried at least 5 different versions of samsung usb drivers, nada.

I tried this on both the win11 pcs and the win7 one to no avail.

I tried putting the firmware in zip format renamed "update.zip" in the root of the micro SD card and using "Apply update from SD card" via recovery, it just shows

E: [libfs_mgr]Failed to mount /sdcard: Invalid argument

E:

E: -- Couldn't mount /sdcard.

E:

Install from SD card completed with status 1.

Installation aborted.#1

To sum up the recovery mode:

- Reboot system now: bootloop;

- Reboot to bootloader: download (?) mode;

- Apply update from ADB: waits for "adb sideload" but can't connect to pc so it eventually fails and goes back to recovery;

- Apply update from SD card: see above;

- Wipe data/factory reset: does what it says, I guess;

- Wipe cache partition: same here;

- Mount /system: displays "Mounted /system." at the bottom of the screen;

- View recovery logs: shows logs containing a plethora of incomprehensible (to me) data;

- Run graphics test: does its thing;

- Run locale test: also does its thing;

- Power off: only way I know of to turn the device off and to keep it that way.

I tried going the QPST/QFIL route as I've found a "prog_ufs_firehose_8998_ddr.elf" that seems to match the code for my snapdragon 835 but the tablet can't go into EDL mode as it just starts bootlooping.

I tried seeing if the "charging logo" way of starting the device actually was an EDL mode in disguise but it wasn't, sadly.

My situation now is this: I can buy an EDL cable for 22€ (which I have no idea on how to use), I can buy a mystery meat main board from aliexpress for 55€ and do the swap myself or pay samsung 280€ for the part and for them to swap it in my place.

I am leaning on the sketchy mobo from aliexpress but if any of you here have any clue on how to go about this that doesn't involve spending money and waiting a month I would be extremely, profoundly grateful.

I've literally spent 12 hours trying everything and anything to fix this, three samsung technicians gave up on this and you, yes you, could be the second coming of jesus descended from heaven to show us how it's really done.

Pls halp