It is possible that you might still need to do a testpoint procedure to get into EDL.
4th category brick – phone status which does not allow to boot into next modes: Recovery, Fastboot, FTM, EDL. In Windows Device Manager the phone detects as ZTE Handset Diagnostic Interface(DFU) (COM...) whrn you connect it via USB cable. Any of possible manipulations give the same DFU mode (even when you force to install Qualcomm HS-USB QDLoader 9008, in reality it is still a DFU mode).
Please thank Vick78 on the other thread. I've been endlessly sending people there to fix their phones, and it works like a charm.
All of this is at your own risk, however obvious that may be... If you don't think you can make it, take it to someone experienced and show 'em this guide.
Patience is key! Be really careful when doing this, or you can break something inside and lose functionality. Flex cables are awful.
0) Know your Model:
Turn your phone around and see what model it is. If you screw up and flash another model's ROM you can lose your IMEIs.
In some cases (AliExpress) the phones come with A2017G software even though they are A2017 models. Just beware.
1) What you Need:
• A Windows PC with (preferrably) 64-bit support. Win7 will do, although Win10 may make stuff slightly easier. If it is a tower PC, use the rear USB ports, not the front ones!
• Your corresponding FULL_EDL package. Download it from @WesTD 's Latest Stock ROMs thread. (Thank him too! )
• MiFlash. Get it from Yandex or Mega, same file. Thanks @djkuz for the link.
• Metal paper clip or needle to short circuit the test point.
• Tiny Phillips screwdriver or at least a knife, to get the screws off.
• Stock USB cable, or at least one that works good with data transfer.
2) Disassembly Video
JerryRigEverything made a full teardown video. Watch the teardown part a couple of times (up to 3:40) until you're familiar with the parts. You don't have to take the speakers or the USB-C module off though, just keep them there.
3) Teardown Hands-On
Images are also from Vick78's thread.
Make sure that the phone is completely off before starting! Also take the SIM card tray off before separating the screen from the back housing or you'll break something
a) Take the speaker grilles out by prying on the edges. You don't need a heat gun for this. Remove the black material to expose the screws, but be careful not to break it if possible, because it protects the speakers.
b) Remove all the screws and VERY CAREFULLY separate the screen from the back housing, to avoid breaking the FP sensor's flex cable. After that, disconnect the FP cable with your nail or some preferably non-conductive thing
c) Take the protective metal piece out, then disconnect the battery, USB-C and display/power connector, then get all those screws out. Put them somewhere so that you won't lose them (piece of tape, maybe a magnet).
d) Take the motherboard out and disconnect the antenna wire that's below it, on the lower part.
e) Disconnect the rear camera. Leave the front one connected.
And now you can see the TEST POINT that you have to short
f) Since the testpoint is in the back of the motherboard, and you need to have the battery and USB-C connected, I advice you to pry the battery off. You can rupture it very easily though. If you don't want to do it, don't worry, it is possible to make without taking it off, but you might break a flex cable and, honestly, it's much harder to hold the connection on the test point while the mobo is facing downwards.
If you will pry out the battery, be REALLY careful and don't force it.
g) Put the motherboard with the test point facing towards you. Connect the battery and the USB-C module to it, and the USB-C cable to the USB-C module (But NOT to the PC yet!). Be VERY GENTLE with the "little lego connectors" as I broke a couple of pins from the USB-C connector (It still works fully, I believe they have redundant pins in case someone like me screws up)
4) Connection to the PC
Before flashing, we need to make sure that the drivers are the correct ones.
- Open Device Manager (if on win10, right click on the start menu button and select device manager), find "Ports (COM & LPT)", and open it. Leave Device Manager open for now.
- Find an USB port on your PC that you can reach while you short circuit the test pad. If you have a desktop PC, it has to be one of the rear ports (NOT the front ports, those have a lot of interference) and they should be USB 2.0 if possible.
- Take the clip and connect the test pad to the big chunk of metal that's right beside it:
-Insert the USB cable (previously connected to the phone) to your PC's USB port.
-Watch Device Manager now. The phone should appear as "Qualcomm HS-USB QDLoader 9008". If it does, just go to the next point. If it doesn't, see if it is called "QUSB_BULK" under USB devices (This happens if you used Zadig). If this happens, find the QUSB_BULK device, right click, Uninstall device, Delete the driver software for this device. After that disconnect the cable from the PC, disconnect the battery, and connect it again; and redo the clip thing up to this point. The correct driver should install itself.
- Open MiFlash, keep it ready
- Unpack the FULL_EDL file to a folder with the same name, then open the folder and make sure that the files are directly there (i.e. they aren't inside another folder), put it somewhere, and select it from miflash ("select" button, select the folder).
- Hold the connection with the clip, as stated in the image above
- Click on Refresh from MiFlash, as soon as it detects a device hit "flash"
- If all goes well, it should say "send configure command". Wait 3 seconds and get the clip out. If it doesn't get to this part or if it fails, just disconnect it from the PC, disconnect the battery and reconnect it, and try again. Do this until it succeeds and it flashes. You might need to do this more than 5 times! If it doesn't work, try leaving the test pad connected for more or less time, like 2 seconds, 2.5 seconds, 3.5 seconds, 4 seconds... But 3 seconds works for most.
-If the flashing works, once it ends, go to the recovery and factory reset the phone. Otherwise there might be conflicting information in /data.