I had mm stock 10d ROM then I upgraded to 20a using LGUP KDZ method by using uppercut trick. I wanted to enjoy Fulmics 1.5 (for my H830), but was newbie so had no idea about rooting it and installing (Because all available guides were actually complexed or I was impatient to read other things except main procedure). So I did something strange and Fulmics was installed over 20a ROM, because I was unable to wipe internal storage due to that decryption thing.
So I thought, I should go back to stock by using LGUP and retry the procedure with more focus. This time LGUP didn’t know my phone, not with that uppercut too. I thought that’s because I unlocked bootloader and must first try to lock it, and try again with LGUP. I retried with locked bootloader and failed again.
(Remember, LGUP or any other tool have nothing to do with back to stock thing. You can go back to stock whether you are bootloader locked or unlocked, it has no power of stopping you.)
1: LG G5 stuck on download mode and it is now not being recognized by LGUP and you can’t do anything, because no other tool is available.
2: You installed a custom ROM and now LGUP is not recognizing it. You want to go back to stock and can’t do it.
3: Anything bad happened during flashing process, PC restarted, phone went off or whatever. And now you can’t bring it back to life.
Other cases you faced.
Read 4th post before proceeding,
Before asking a question, first, see FAQ in 3rd post. In that way you can save a lot of time.
For Video Guide refer to 4th Post
4: Stock ROM for your device.
5 : LG Flash tool (the one used to bring LG G2, G3 back to stock).
I used 20a KDZ because I had it already and it was nougat with vulnerability to root and flash TWRP.
6: LG Firmware extract tool
In 2nd post
Most tools can be found in attachments of 2nd post.
Uninstall all other tool, previous driver (including other phone’s too). Restart PC
Just to avoid problems. I tried this process many times on Windows 10 64-bit and it always worked for me. So it has no problems with new Windows OS.
Now follow procedure in exact order.
1: Install LG drivers.
Put Phone in download
(Hold Vol+ and connect to PC while it was powered off).
Wait until it finishes installing drivers. Change COM Port to 41.
( Refer here for changing this, If you can’t understand that.)
Now DC it from PC and keep it staying in Download mode.
2: Install LG Flash tool and copy megalock.dll to installation directory or it won’t work.
3: Install LGH-H830_DLL, LGH850_DLL and LGUP_Store_Frame_Ver_1_14_3.
4: Extract LG Firmware Extract and copy Stock KDZ to that folder.
5: Run WindowsLGFirmwareExtract.exe
A: Click on “KDZ file” open and select stock KDZ.
B: Mark File Name. It will select all files. Click on extract KDZ button. Wait till finished. Now quit the program.
6: Run LG Flash tool. Select Manual mode. Click “…” for dll and select LGUPc.dll from that KDZ extracted folder.
A: Click on add button of S/W, Select “All Files” from pop up window. Now ““.KDZ”” file will be shown, select that ““.KDZ”” file, press open button, click on “OK”
B: Begin download by pressing that big “Yellow Right Arrow”. Wait until it finishes loading.
C: Connect phone when LG Flash tool says “Waiting for connection”. Make sure phone is in download mode and COM port is 41.
D: After a while it should fail the process, that’s fine. Just DC Phone, do not turn it off.
7: Exit LG Flash tool and Run it again. Select Manual Mode. This time select LGUP_H830.dll (Select as per your model e.g H850.dll for International variant) from LGUP
(Download it from 2nd post, then extract and select as dll for this step only.)
Folder. On S/W section first click on “Remove All” to erase old selected KDZ from tool and select “.DZ” (not “.KDZ”) as S/W from extracted KDZ ROM.
A: Press ok, Select on big “Yellow right arrow”. This will be loaded quickly. Connect the phone again. This time the process will get started. Wait till it gets completed.
Note: This flashing process will go up to 150% so don’t get nervous or don’t DC phone.
B: Phone will be restarted automatically. A big “2” will be shown. Wait till it gets converted into “3” and tool will say pass.
if so pull battery and start phone normally.
If it is not converted into 3: Happened to me for first time.
(First Quit LG Flash tool)
Pull battery, reboot again into download mode. Run Uppercut, say “Yes” to consent, LGUP will be started automatically, Now LGUP will recognize the phone. Click on upgrade, Press “…” and browse stock KDZ ROM and select “.KDZ” stock ROM (not “.DZ”)
Select Upgrade because Refurbish won't work with uppercut.
Press Start. Download will get started. Wait until it finishes. Now Your Phone is back to life.
Ask If anything wrong happened, I will try my best to help. I used this method on my device, LG G5 T-Mobile variant AKA H830. It should work for others.
Hit Thanks, if I helped you.
If I forgot to give credit to anyone who is related with these tools, please let me know and I will be happy to name them.