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Use a bench power supply (stop using BS chargers)

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  • Use a bench power supply (stop using BS chargers)

    Hi, although im not very active on this forum i have something that i think people may find useful.

    You need to take a genuine Magsafe cable and connect it to a bench power supply. Use it as your charger. You can set voltage, easily turn it on and off, but most importantly:
    You can measure current. Mine has a Magsafe 1 and magsafe 2 cable attached, Gets a green light, acts like a normal charger, and can be set up to 20V for 15" retina's

    To give you 3 examples:

    2015+ apple laptops dont turn on the fan automatically, so how do you know if its quater fan spinning without measuring a bunch of crap? (as far as you know its stuck in S5) Look at the current, it will literally show you that its power cycling.

    Something has an SMC related issue (No S4/3) you will see a different current being drawn by the board, In my case when i get 8.1V or am missing SMC_Reset_L, i will have 0.0031A vs 0.0036A.

    If you have a bad U1950 but all S0 your current should be around 0.2A rather than 0.5-0.6A, The CPU wont be getting hot, In the same case, if you have a bad S0 rail, you will get a simalar reading and instantly know to check ALL_SYS_PWRGD and U1950.

    I fixed a 2915 with a 5vs0 short recently, but at first glance it was stuck in S5, no fan spin, no s4, but i was able to see the machine was trying to turn on, the current would jump from 0.036A to 0.1A or so, This meant rather than searching the SMC related or S5 related stuff, i knew it was trying to boot but shutting down, probably some current sensors somewhere, therefore probably a short circuit, I started looking at the rails and quickly found a bad cap on 5v_s0
    It was a quick fix that would have taken much longer if i wasn't observing the motherboards current draw.

    If you have a short circuit somewhere you will be able to identify it without having to measure stuff.

    Essentially this will give easily accessible information to help pinpoint diagnosis, its similar to using diode mode to figure out what part of a backlight circuit isnt working (but more useful IMO)
    If this becomes commonly used it should (in theory) become far easier to pinpoint complex issues.

    P.S: I havent bothered figuring out how to connect USB C macbooks to a bench supply as a charger.

    I hope this is adopted by not only learners but people who know what there doing. It will make your life allot easier.

  • #2
    You fail to mention the adapter wattage is very important and that is determined by the tip. It is not just the voltage that is important here. Also an original charger will monitor the current before turning on full output voltage, so when a board works from the bench supply it may not work from a genuine charger.

    For diagnostics only an 85W magsafe tip should be used as all boards will power on from that.

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    • #3
      Originally posted by dukefawks View Post
      You fail to mention the adapter wattage is very important and that is determined by the tip. It is not just the voltage that is important here. Also an original charger will monitor the current before turning on full output voltage, so when a board works from the bench supply it may not work from a genuine charger.

      For diagnostics only an 85W magsafe tip should be used as all boards will power on from that.
      Thanks for providing the information i missed.

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      • #4
        nice post thanks,

        how did you connect your charger on you BPS

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        • #5
          theres only a positive and negative to connect from a MagSafe cable. The controller is in the tip.

          So just cut of a cable from a charger and wire up the positive and ground correctly.

          Ive added banana plugs to mine so I can remove it from the psu easily.

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          • #6
            Originally posted by ALB-Repairs View Post
            theres only a positive and negative to connect from a MagSafe cable. The controller is in the tip.

            So just cut of a cable from a charger and wire up the positive and ground correctly.

            Ive added banana plugs to mine so I can remove it from the psu easily.
            Thanks thought so, but didnt have a donor cable yet

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            • #7
              And tell your customers to not try to fix their own chargers... Guy died here last week opening his charger immediately after pulling it out from the outlet. Charged caps.

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              • #8
                Wow.
                Yeah, i tell all my customers not to bother trying to re-cable or fix chargers.

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                • #9
                  Does anyone use usb c on Lab PSU? if so do you just connect +V and GND? i accidentally sold my charger but i have some type c cables
                  Read more........

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                  • #10
                    No that wont work (as far as im aware), You need to read up about USB-C type power delivery and learn about Chanel configuration pins and understand it before injecting voltage to a USB C based laptop.

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                    • #11
                      i use Dell power brick and this pass-through multimeter. it is really cool since it can actually graph amp usage, so you can see detailed power sequence
                      https://www.amazon.de/USB-Spannungsp...b+tester&psc=1

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