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820-3662 LD, worked for a while after UC now ON-OFF loop

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  • 820-3662 LD, worked for a while after UC now ON-OFF loop

    Hi guys,

    this one came with LD which was almost invisible except some patches here and there.. I UC and the board started but would not detect the SSD drive.

    I connected a USB boot drive and started from there without issues until the system shut down before completely booting and is in boot loop ever since.

    I measured Y1905 and that is getting 0.9 to 1V and also all necessary voltages seem to be present at U1900 but I cant measure 32Khz neither 25MHz coming from the chip.. the oscilloscope shows some irrelevant readings which jump around but not steady frequencies... also pins 15 (SYSCLK_CLK25M_TBT) and 16 looked a bit dodgy ...not shiny like the rest.

    BIOS chip area looks good, power comes to pin8.

    Could it be the clock chip since its so sensitive to water damage?


    george



  • #2
    This will be a corroded trace or resistor. Look closely in the areas that were affected.

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    • #3
      as an update I heated up the SMC with some flux and did another UC. It works.. for now

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      • #4
        well that didnt last long - I got lines on the screen, random reboots, SSD not found etc etc.. so I had to reflow the CPU and PCH.

        NOW it works and completes the installation of Yosemite OR El Capitan but upon reboot I either get to Recovery and I can only re-install OR it boots again to a fresh installation procedure from the USB stick.

        Tried to google this behavior but I only find similar stuff irrelevant though.. i.e. upgrade to El Capitan from Yosemite and have unsupported kexts..

        No one seems to have my problem?

        Any ideas?
        Attached Files

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        • #5
          PRAM reset usually solves that.

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          • #6
            I think I did it but will do again...

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            • #7
              OK duke, I did not manage to install OSX normally and I had to use RESTORE from Recovery mode/Disk Utility to copy a working installation to the internal SSD. This worked fine with a small glitch.

              Upon reboot or turn-on it takes around a minute to detect the SSD and then boot. After that everything seems normal.

              see: https://www.youtube.com/watch?v=kQ0c...ature=youtu.be (65 seconds video)


              Since this is still a mystery itd be nice to have some more ideas why its behaving like that.. Unfortunately no spare SSD to check if that is the culprit..

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              • #8
                Hi, system will always try to boot last assigned/selected startup disk. It usually takes time to detect ssd when prior to that you use hdd usb boot for testing, live os, or asd efi/os.

                Go to system preferences, startup disk and select your booting ssd drive even if it´s the only one.
                PRAM should also fix that.

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                • #9
                  Originally posted by jadao View Post
                  Hi, system will always try to boot last assigned/selected startup disk. It usually takes time to detect ssd when prior to that you use hdd usb boot for testing, live os, or asd efi/os.

                  Go to system preferences, startup disk and select your booting ssd drive even if it´s the only one.
                  PRAM should also fix that.

                  the preferences did it. It now works properly but it seems the SSD has issues - you cant install anything new to it. Works great with different SSD.
                  thank you!

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