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820-3330 intermitting startup and orange light - fan twitch if dead

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  • 820-3330 intermitting startup and orange light - fan twitch if dead

    This 820-3330 can work perfektly fine. Unfortunately only randomly it starts and works. The rest of the time its dead with just an green light (orange light is just there it it decides to start) and fan twitch ~ every 1 second. I can hear a clicking noise (i guess from a transistor?!) if the fans twitch.
    I checked a few things and as sometimes even the green light was fading away i replaced ISL and SMC already. Now the green light is there every time (orange light still only if it starts) but still starts only randomly...
    I checked all rails for shorts and PP1V05_TBT has just 17 Ohms to GND (not sure if thats ok?). If it starts there is 1,1V on that line...
    So i am confused at this point.

  • #2
    You can remove U3815, if you have any doubt with PP1V05_TBT rail.
    I don't know which value should get there.
    17 ohms could be normal, beeing Thunderbolt core power rail.

    You must post some voltages, signals level when board doesn't start...

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    • #3
      Thank you for the answer. I didnt know where to start at this. Every Rail except 3V42 was pulsing with a 85W Charger (eg. PPBUS is jumping between 10.X V and 12,6 V) This board should start from a 85W charger without battery if i am right. I tested with customer battery (just in case) but still the same. Just in case i tested a different battery and it seems to work from that battery most of the times but still not from the charger. Also sometimes it turms itshelf right back off after a few seconds (sometimes it chimes - sometimes is turns off earlier. This happens from battery and battery + charger). I traced this back and came to D6990 that was leaking charger voltage to the battery (0.2 V in diode mode but it should read OL between pin 1&2) So i replaced D6990 (now its reading is OL) And it seems to start and work with the new battery.
      Still sometimes pulsing and fan twitch without batterty sometimes working fine...
      Last edited by Fizzl92; 6 days ago.

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      • #4
        if I correctly understand, machine gives sometime problems on charger only.
        You must post some voltages in that moment.

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        • #5
          Yeah check your current sensing circuit too resistance between 17/18 and 27/28 of the ISL

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          • #6
            It gives the problem randomly on charger as well as charger and battery. With battery alone it did not happen.
            Current sensing is fine at the ISL pins.
            My Problem is that every Rail (except 3V42) seems to be present but pulsing. Even PPDCIN_G3H_CHGR is pulsing between 16.0 V and 16.2 V with charger and battery plugged in but only green light... Same with charger only. 3V42 is the only steady rail at 3.40 V.
            Even 5V_S0, Vcore and DDR rails are pulsing. Some pulse more and some less... (eg. 5V_S0 is pulsing between 0.4 V and 1 V - PPBUS is pulsing between 10 V and 12.6 V)
            So i dont know what to measure/report to you. Have never had anything like this as is works perfektly fine just a moment later...

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            • #7
              OK, so you have charger related issue.
              First of all try known good working 85W charger.
              You can also try bench power supply, with the cable removed from 85W charger.
              Change Q7080, just in case.

              Do you get steady high CHGR_ACOK signal?

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              • #8
                Changed Q7080 - no change. I tryed defferent, known good chargers ( 1x 85W that works with other devices and 1x 60W with customer battery on Bench power supply)
                With the same chargers it works a moment later randomly...
                If i plug in a battery everything is fine and it works instantly. Unplug battery and its dead again!?
                CHGR_ACIN = pulsing 3.8 V - 3.9 V
                CHGR_ACOK =also pulsing 2.2 V - 2.3 V
                Last edited by Fizzl92; 5 days ago.

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                • #9
                  Remove C7011, see if anything change.
                  Use o-scope and check how much drop these signals.

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                  • #10
                    Unfortunately the next time i have access to a scope is on monday. I removed C7011 and now it works with charger too. But i had this situation already a few times and later the same day the problem returms. Maybe its a heat related problem?
                    I'll report back if it dies again and post scope readings on mondey if problem returns.
                    Thank you.

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                    • #11
                      Unfortunately removing that cap didnt work. Now its back to fan twitch. I´ll report scope readings on monday.

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                      • #12
                        As far as i can tell they drop down all the way to 0V. But it seems like my CRT is having some problems as it istn´t showing 0V if i do not measure anything. Its lower than the screen can show without me measuring something no matter what i do... So i am not sure if they acrually reach 0.0V.

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