No LTE bands 12/17 on VS996 -> US998 Frankenstein V30 - LG V30 Questions & Answers

I converted my Verizon VS996 to a US998 with the Frankenstein method: US998 10b KDZ -> US998 20b -> Unlock + TWRP -> US998 20e. I get LTE on T-Mobile and AT&T on bands 2 and 4, but I never get band 12/17. I notice poorer reception overall too. The frankeinstein process is supposed to enable all the LTE bands the US998 has but it isn't accessing them. I tried unlocking LTE bands using the hidden menu while rooted, and selecting 12, 13, 17, 29, 30 leaves me with no LTE coverage. I also set the RAT selection to LTE only and I only get signal when selecting band 2 or 4. Also I see no band 12/17 cells on Rx Monitor.

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My issue is now fixed I'll explain in detail later. For now.
What I've learned:
-The old stock modemst1 and modemst2 partitions remain after the cross-flash Frankenstein method*
*Unless the partition maps were conflicting/changed, all according to PrimaryGPT and the other GPT partitions. (modemst partitions would be rebuilt in a new place)
-These old modemst1 and modemst2 partitions are locked with the stock LTE bands, potentially causing issues, as in my case.
-Eg. the VS996 has no support for band 12, so it might not work after cross-flashing to US998
-The modemst1 and modemst2 partitions aren't always rebuilt well after erasing it with dd (I took a backup of modemst1 and modesmst2 after wiping with dd, opened them with hex viewers on windows, and realized they were not blank partitions with zeros. I guess these partitions are meant to be minimally read/writed on. modem partition was all zeros)
-All the V30 phones have identical modem chips, the bands are software locked
-My method could allow LTE band 71 unlocking... for use on T-Mobile. Except the H932 modem didn't work when I tried it before, but didn't bootloop/brick on my VS996 -> US998.
-abl and ablbak are the key partitions for bootloader unlock & check, booting, and fastboot access
-Leaving these two partitions alone from US998 when flashing to H933, AS998, or H931 leaves you with fastboot access
Process:
1. Flash the VS996 to US998 with unlocked LGUP in Partiton DL mode
2. Install TWRP via fastboot
3. Boot TWRP via fastboot
4. Factory reset, wipe data, cache, dalvik/art-cache, and internal storage. Repeat twice
5. Format/wipe data, type yes
6. Reboot to recovery
7. Flash Magisk 17.3, Disable_Dm-Verity_ForceEncrypt, and lg-rctd-disabler. (THIS ORDER. If this is not done, TWRP will be reverted to stock, eg. would only factory reset when triggered)
8. Boot system
9. Boot into recovery, factory reset, wipe data, cache, dalvik/art-cache, system. Repeat twice.
10. Format/wipe data, type yes
11. Wipe modem, modemst1, and modemst2 with dd:
Code:
dd if=/dev/zero of=/dev/block/bootdevice/by-name/modemst1 bs=16384
dd if=/dev/zero of=/dev/block/bootdevice/by-name/modemst2 bs=16384
dd if=/dev/zero of=/dev/block/bootdevice/by-name/modem bs=16384
(Repeat above commands 3 times)
12. Reboot into recovery, flash my H931_20d.zip made from an H93120d dump.
13. Flash Magisk 17.3, Disable_Dm-Verity_ForceEncrypt, and lg-rctd-disabler. (THIS ORDER. If this is not done, TWRP will be reverted to stock, eg. would only factory reset when triggered)
*Most importantly, the H931 ZIP contains 36 stock H931 20d partitions. The modem, modemst1, and modemst2 partitons are critical in configuring/running the modem to its instructions stored within modemst1 and modemst2! These will ensure the converted phone has all the available LTE bands of the H931, including band 12, which is what I was not getting before.
*Guide isn't final, there are no links yet. I will update it later.*

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patato21 said:
My issue is now fixed I'll explain in detail later. For now.
What I've learned:
-The old stock modemst1 and modemst2 partitions remain after the cross-flash Frankenstein method*
*Unless the partition maps were conflicting/changed, all according to PrimaryGPT and the other GPT partitions. (modemst partitions would be rebuilt in a new place)
-These old modemst1 and modemst2 partitions are locked with the stock LTE bands, potentially causing issues, as in my case.
Click to expand...
Click to collapse
Glad your issue is fixed but I disagree with some of your premise. If you flash from VS996 to US998 via DL Partition mode, the old modem partitions can't remain. You are overwriting all the partitions (including modem) with US998 KDZ via Frankenstein.
Tell me how you cross flashed?
In the Frankenstein thread you flash any North American variant (except H932) to Nougat US998 first via DL Partition (choosing all partitions), then do Master Reset and then upgrade to US998 Oreo. Some, like Canada H933, have to DL Partition at both stages. So, they have overwritten their partitions TWICE.
If you correctly DL Partition any North America V30/V30+ to US998 you WILL have these bands:
http://www.lg.com/us/cell-phones/lg-US998-Silver-lg-v30
US998
CDMA: 800 MHz CDMA
2G GSM: 850/900/1800/1900 MHz
3G UMTS (HSPA):850/900/1900/2100 MHz
4G LTE Bands: 1/2/3/4/5/7/12(17)/13/20/25/66
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patato21 said:
-abl and ablbak are the key partitions for bootloader unlock & check, booting, and fastboot access
-Leaving these two partitions alone from US998 when flashing to H933, AS998, or H931 leaves you with fastboot access
Click to expand...
Click to collapse
Very interesting.
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patato21 said:
11. Wipe modem, modemst1, and modemst2 with dd
Click to expand...
Click to collapse
What is dd?

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ChazzMatt said:
What is dd?
Click to expand...
Click to collapse
Code:
dd if=/dev/zero of=/dev/block/bootdevice/by-name/modemst1 bs=16384
dd if=/dev/zero of=/dev/block/bootdevice/by-name/modemst2 bs=16384
dd if=/dev/zero of=/dev/block/bootdevice/by-name/modem bs=16384
It wipes the modemst1/2 partitions. They're not reliably wiped this way.

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dd = diskdump. name explains it

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seadersn said:
dd = diskdump. name explains it
Click to expand...
Click to collapse
i call it diskdestroyer

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patato21 said:
It wipes the modemst1/2 partitions. They're not reliably wiped this way.
Click to expand...
Click to collapse
try wiping these partitions with fastboot erase. see if these commands are available. they should be, never used erase on v30 til now. but worth a try.

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Chazzmatt, I will pay you to do this to my phone!!!
Chazzmatt, I will pay you to do this to my phone!!! Please help me out!!!