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Dell Precision M4800 posts but wont boot, no SVC tag

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    #1

    Dell Precision M4800 posts but wont boot, no SVC tag

    I've been lurking around the forums for a long time and absorbing the knowledge.

    I knew this day would come eventually xD, just didn't think it would be because of something like this.
    I'm at an issue that I can't solve and i have not found anyone having a similar problem.

    I have a Dell Precision M4800. The laptop POSTs and I can Press F2 or F12 and those get registered, but the laptop doesn't enter BIOS.

    Instead, it always goes to a screen which says:
    WARNING: The Service Tag has not been programmed. This system will not function properly without a Service Tag.

    The setup utility will launch the Service Tag installer.

    To continue press F1 key

    No key except the F1 does anything and pressing F1 gets me to a backlit black screen with nothing on it and it just sits there untill shut off.
    Upon reboot same story.


    What i've tried:
    Clear CMOS.
    Unplugged all unnecessary stuff, leaving only essentials (Mobo + CPU + RAM + Screen) on.
    Desoldered MAIN and EC ROMs and make a backup, then flashed EC and MAIN from this post: https://www.badcaps.net/forum/showpo...52&postcount=8
    Desoldered MAIN and EC ROMs from a working M4800, made a backup of them and soldered them to the faulty one (thinking it might be an issue with the chip) and since the working one had Service Tag already set i thought i would be able to pass the error.


    None of the above gave me any progress.
    In the past i had bought replacement Dell boards that came without the Service Tag set and i was always able to set it in BIOS afterwards.

    I'm suspecting the service tag might be saved somewhere else in the motherboard too, or perhaps there is something blocking the communication?

    I'm really out of ideas what to try anymore, so I'd be very gratefull for any input
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    #2
    Re: Dell Precision M4800 posts but wont boot, no SVC tag

    Nevermind I've just figured the issue... there is something most likely wrong with the screen, i've swapped the boards in the chassis and now the working one gets stuck after post logo, and the "faulty" one got to BIOS and i was able to set the Service Tag xD

    Just posting this here so future readers might solve their problem.
    Now have to assemble them both back up and check if perhaps the EDID is corrupt on the "faulty" one :P

    Comment

      #3
      Re: Dell Precision M4800 posts but wont boot, no SVC tag

      Yep can confirm, the issue was definitely with the screen, i'll try to see if perhaps the EDID is corrupted.

      Comment

        #4
        Re: Dell Precision M4800 posts but wont boot, no SVC tag

        EDID was corrupted, but i can't rewrite it with i2cset it appears to be write protected.
        I've just replaced the screen and we are good

        Comment

          #5
          Re: Dell Precision M4800 posts but wont boot, no SVC tag

          Very interesting feedback. Thanks. Can you physically see the I2C eeprom on the non-working screen? Most likely it is a 8 pin SOIC device that could be carefully removed and cloned or reflashed with an external programmer.

          Comment

            #6
            Re: Dell Precision M4800 posts but wont boot, no SVC tag

            No i don't see it, is it possible that the screen would not be write protected in a different laptop? I've never had a wirte protect before, although this is also the first time i've encountered EDID fault in a precision laptop.
            So far it's been mostly in alienwares.
            I've put it aside and i'll get back to it when i get a different brand laptop to try and reflash it with

            I've got another exactly the same display (N156HGE-L11) and i've pulled EDID from that one and compared it with the broken one... the only difference is at the 0x13 address where the faulty one has a 00 and the good one has a 04.

            If anyone needs it in the future, the good edid for N156HGE-L11 is:

            0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
            00: 00 ff ff ff ff ff ff 00 0d ae b1 15 00 00 00 00 ........????....
            10: 01 16 01 04 90 22 13 78 02 31 d5 9f 56 58 95 27 ?????"?x?1??VX?'
            20: 15 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01 ?PT...??????????
            30: 01 01 01 01 01 01 96 3b 80 32 71 38 3e 40 5a 3c ???????;?2q8>@Z<
            40: 69 00 58 c2 10 00 00 1a 9b 25 80 ee 70 38 23 40 i.X??..??%??p8#@
            50: 35 23 35 00 58 c2 10 00 00 1a 00 00 00 fe 00 56 5#5.X??..?...?.V
            60: 43 4d 38 58 02 4e 31 35 36 48 47 0a 00 00 00 00 CM8X?N156HG?....
            70: 00 00 41 31 9e 00 00 00 00 02 01 0a 20 20 00 05 ..A1?....??? .?

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