[G4 General] tacticalcoconut:
Hallo US991 friends and any others this may help. I decided to revive the old potato lying around and inevitably ended up memorizing pixel by pixel the Lineage OS, AOSCP, and stock loading screens before I realized throwing the G4 in front a fan wasn't doing enough to fix it.

The secret sauce, as [MENTION=5545101]steadfasterX[/MENTION] said in the FAQ, is to flash the specific modem bin using fastboot

Here's a N00B friendly guide (assuming you've successfully "unlocked" and installed twrp):

If someone can educate my dumb*** on how to attach files on thread replies, I will attach the US991 modem bin file I extracted from the US991 20c (MM) kdz

NEVERMIND. As mentioned by [MENTION=5545101]steadfasterX[/MENTION], just use SALT to extract. I'll leave this method up just in case

Here's how to do it. This app only runs on Windows:

https://xdaforums.com/showthread.php?t=2600575

1. Download and extract WindowsLGFirmwareExtract from the above forum post. Run the app.

2. Click the KDZ open button to browse and select the kdz, then mark the checkbox only for the .dz file. Hit extract KDZ

3. Click the DZ open and select the dz that was extracted in the above step (it should be in the same folder as the firmware extract app). Mark the checkbox only for the modem_xxx.bin file. Extract dz.

4. Once again, the extracted modem bin file should be in the same directory as the application.

To flash this bin over fastboot (on linux, after you put device in fastboot mode):

1. cd to the location of the modem bin file

2. Make sure the device is recognized (you should see some sort of id or something whatever it's called is im a nuub):

fastboot devices

3. Then run (replacing the last parameter with whatever you named your bin file):

fastboot flash modem US99120c_modem_32768.bin

----------------

My complete working process for stock v29:

1. Wipe data, cache, Dalvik.

2. Format Data. Reboot recovery.

3. Flash stock v29 USU ROM. Reboot into recovery.

4. Flash Baseband. Power Down device.

5. Use fastboot to flash modem bin file (follow guide above)

6. Power device off, and turn on and let load

7. 10-20 seconds after power on you'll hear the LG chime, the blue light up top will blink, and the LG load animation will be present. After 5-10 min, you'll see the "Anrdoid is starting..." screen. If all went well, it wont reboot and do the same thing again and again, and you'll be taken to the setup screen.

My working process for Lineage 15.1 (same process probably for all other Custom ROMs, idk I only tried Lineage).

1. Download the GPT compatible version of your intended Custom ROM (Mine was H811).

2. If it's not USU compatible already, you'll have to modify the update-script (or updater-script whatever its called) as mentioned in the FAQ. Search around for how, but you'll find the relevant file in META-INF/com/google/android.

3. Wipe data, cache, Dalvik.

4. Format Data. Reboot recovery.

5. Flash Custom ROM. Reboot into recovery.

6. Flash N modem. Reboot into recovery (rebooting recovery in between flashes DOES seem like it could make a dIfference so make sure you try it!!)

7. Flash Baseband. Reboot into recovery.

8. Flash OpenGapps (download from https://opengapps.org/), ARM64 (8.1 for Lineage 15.1). Power down device.

9. Use fastboot to flash the modem bin file (follow guide above)

10. Power device off, and turn on and let load

11. 10-20 seconds after power on you'll see the boot screen. After 8-12 min, you should be taken to the setup screen.

(I played around with LOS 15.1, and LTE, calls, texts, camera, etc were working, but the darn flashlight wasn't.)

Hope this helps!

Finally major props to [MENTION=5545101]steadfasterX[/MENTION] for not only putting in the time to make this, but also taking the time to document it well enough such that even an iPhone wielding (gasp. sorry the homies use iMessage) freshman could figure this out within a few hours!!!

---------- Post added at 02:44 AM ---------- Previous post was at 02:26 AM ----------

Oh and this may have just been me screwing up, but when I installed and was using TWRP Preview 123, my PC would merely list the phone as "LG USU" after flashing my US991 specific baseband. Switching to Preview 109 solved it, with the phone showing up as "LG US991" when in TWRP.