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Thread: Galaxy S20 Ultra (SM-G988U) - Multi-CSC Flash Help

  1. #1
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    Galaxy S20 Ultra (SM-G988U) - Multi-CSC Flash Help

    Hi everyone! Hoping for some help flashing my Galaxy S20 Ultra (SM-G988U) to a multi-CSC ... Well, the flashing seemed to work fine. I can't get the phone to change its CSC to the SIM I'm using.

    So as I said, I'm using the SM-G988U that I purchased from Xfinity Mobile (CSC code is CCT). Yes, it's been fully network-unlocked.

    I downloaded and flashed the latest firmware with CSC code XAS. This should be the "multi-CSC" firmware I need so the phone will make appropriate changes depending on which SIM I'm using.

    After flashing the XAS firmware, I put in an AT&T SIM (instead of the original Xfinity Mobile SIM). And the phone does NOT go through the process of changing its CSC/rebooting/etc. It still boots with the Xfinity Mobile logo, has Xfinity Mobile bloatware, and still shows my network operator as Xfinity Mobile. HOWEVER, the AT&T SIM is working in the phone. The phone number is changed, I can make/receive calls/texts, and the data works.

    But I'd really like to get the damn phone to change its CSC from CCT to ATT using the XAS firmware I installed.

    Any help? Much appreciated!

  2. #2
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    Quote Originally Posted by bourretbrandon [ Login above or register to see download links. ]
    Hi everyone! Hoping for some help flashing my Galaxy S20 Ultra (SM-G988U) to a multi-CSC ... Well, the flashing seemed to work fine. I can't get the phone to change its CSC to the SIM I'm using.

    So as I said, I'm using the SM-G988U that I purchased from Xfinity Mobile (CSC code is CCT). Yes, it's been fully network-unlocked.

    I downloaded and flashed the latest firmware with CSC code XAS. This should be the "multi-CSC" firmware I need so the phone will make appropriate changes depending on which SIM I'm using.

    After flashing the XAS firmware, I put in an AT&T SIM (instead of the original Xfinity Mobile SIM). And the phone does NOT go through the process of changing its CSC/rebooting/etc. It still boots with the Xfinity Mobile logo, has Xfinity Mobile bloatware, and still shows my network operator as Xfinity Mobile. HOWEVER, the AT&T SIM is working in the phone. The phone number is changed, I can make/receive calls/texts, and the data works.

    But I'd really like to get the damn phone to change its CSC from CCT to ATT using the XAS firmware I installed.

    Any help? Much appreciated!
    Hi there

    Could you go to Software Info on your device, screenshot it from top to bottom and post it here?

    Make a screenshot when your ATT-SIM is inserted

  3. #3
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    hi i also want to to flash fraemwair to my device the carent one is the xxu3 and i want to flash xxu1 using odin is it ok to do that

  4. #4
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    Quote Originally Posted by AW123456 [ Login above or register to see download links. ]
    hi i also want to to flash fraemwair to my device the carent one is the xxu3 and i want to flash xxu1 using odin is it ok to do that
    Hi there

    If I see this correct, you're trying to downgrade?
    That's not possible...

  5. #5
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    Quote Originally Posted by henklbr [ Login above or register to see download links. ]
    Hi there

    Could you go to Software Info on your device, screenshot it from top to bottom and post it here?

    Make a screenshot when your ATT-SIM is inserted
    Thank you for the reply and any help. This is the software page while the AT&T SIM is inserted and operational. The last firmware I installed was this one [ Login above or register to see download links. ]

    [ Login above or register to see download links. ]

  6. #6
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    Just wanted to follow-up and let you know I got it fixed up now. The AT&T firmware for the Galaxy S20 Ultra does not contain a "USERDATA" partition. So I found one elsewhere, added it to a normal SamMobile AT&T firmware (which contains BL, CP, CSC, and AP). Then I used a "patched" version of Odin that doesn't do SHA256/device checks to force the firmware onto my phone. Now everything's working brilliantly! No Xfinity Mobile bloatware, no Knox triggering (so warranty is still valid and Samsung Pay still works), and the phone recognizes and accepts OTA firmware updates. The "Service Provider SW Ver" now shows the 3 CSCs as "ATT/ATT/CCT". I know that third one can't be changed because it's the original sales code CSC. But other than that, the phone firmware/features are now AT&T enough for me. No more dropping into HSPA/3G mode during voice calls either.

  7. #7
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    Quote Originally Posted by bourretbrandon [ Login above or register to see download links. ]
    Just wanted to follow-up and let you know I got it fixed up now. The AT&T firmware for the Galaxy S20 Ultra does not contain a "USERDATA" partition. So I found one elsewhere, added it to a normal SamMobile AT&T firmware (which contains BL, CP, CSC, and AP). Then I used a "patched" version of Odin that doesn't do SHA256/device checks to force the firmware onto my phone. Now everything's working brilliantly! No Xfinity Mobile bloatware, no Knox triggering (so warranty is still valid and Samsung Pay still works), and the phone recognizes and accepts OTA firmware updates. The "Service Provider SW Ver" now shows the 3 CSCs as "ATT/ATT/CCT". I know that third one can't be changed because it's the original sales code CSC. But other than that, the phone firmware/features are now AT&T enough for me. No more dropping into HSPA/3G mode during voice calls either.
    Hi there

    I'm glad it has been sorted out for you: thanks for the feedback

  8. #8
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    Somehow this method also managed to change my model number from the original SM-G988U

    [ Login above or register to see download links. ]

    to SM-G988U1

    [ Login above or register to see download links. ]

    I think as long as the firmware matches the chipset (Exynos/Snapdragon), I could turn this into a China phone, or a Canada phone, or any other Snapdragon variant, Not that I have such drastic needs, but it's a bonus. :-)

  9. #9
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    Where did you find the userdata?

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