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Metal chassis laptop (MACBOOK) and ground

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  • #16
    Is your power supply a genuine Magsafe? If not, what is it?

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    • #17
      Originally posted by Mick Bailey View Post
      Is your power supply a genuine Magsafe? If not, what is it?
      No it's a replacement AC adapter but no brand. So it would be the magnetized magsafe plug faulty ? Or just the transformer part ?
      I have to try another power supply before buy it, because they are not cheap...

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      • #18
        Originally posted by tepsamps View Post
        No it's a replacement AC adapter but no brand. So it would be the magnetized magsafe plug faulty ? Or just the transformer part ?
        I was involved in the design and safety approval/certifiction of many a power supply and am not in favor of modifying a power supply that doesn't conform to safety standards.

        So it would be the magnetized magsafe plug faulty ?
        What do you mean with "magnetized"?
        Last edited by Helmholtz; 02-17-2020, 08:09 PM.
        - Own Opinions Only -

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        • #19
          I'm not clear - do you have two different adaptors? you mentioned magsafe (macsafe) as well as a no-brand replacement.

          When you said you used the Magsafe adapter with a 3-pin outlet, did you use the genuine Apple three-pin extension lead with this? It earths via the metal stud - you can see the contact in the slotted part. I haven't personally verified this, but it's reported to fix the tingling/shock issue.
          Attached Files

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          • #20
            Originally posted by Mick Bailey View Post
            I'm not clear - do you have two different adaptors? you mentioned magsafe (macsafe) as well as a no-brand replacement.

            When you said you used the Magsafe adapter with a 3-pin outlet, did you use the genuine Apple three-pin extension lead with this? It earths via the metal stud - you can see the contact in the slotted part. I haven't personally verified this, but it's reported to fix the tingling/shock issue.
            i have only one adapter it has no brand and it's written "replacement AC adapter" on it. And yes i have this cord. But i don't speak about tingling,or strange sensations but about strong shocks, and it blows my 30mA fuse if i put the mac to the ground, i think it's not normal. And i have to put it to ground because of a sound card, if i plug my guitar in the sound card and the mac is not grounded i have a nasty hum which i don't have if the mac is grounded, but on battery.

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            • #21
              Originally posted by Helmholtz View Post
              What do you mean with "magnetized"?
              The little plug is magnetized because it sticks to the mac like a magnet. But that is normal...

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              • #22
                Can you post some pictures of the adapter and lead? A tingle is normal with an ungrounded Macbook, but a shock or tripping of the breaker is not normal at all. The problem with aftermarket power adapters is they often carry fake approval markings and the internal construction can be unsafe. I'd like to know how the three pin lead grounds to the adapter and whether this is actually connected to the DC output in any way.

                Edit: there's a comparison between the knock-off and a genuine charger here: https://lifehacker.com/dont-replace-...off-1825605569

                You can see with the genuine adapter that the earth stud connects to the negative side of the DC supply cable.
                Last edited by Mick Bailey; 02-17-2020, 06:23 PM.

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                • #23
                  Interesting document. Here is my adapter...I cant' find direct contact between the earth stud and a ground pin on the little plug
                  Attached Files

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                  • #24
                    again

                    It's clear that mine does not have the apple on it ...
                    Attached Files
                    Last edited by tepsamps; 02-21-2020, 06:44 PM.

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                    • #25
                      I've seen a few teardowns of aftermarket units and it looks like they leave the ground pin unconnected on many of them. You need two things - a connected ground pin inside the adapter, and the extension cable that has the mains plug ground connected to the metal contacts within the sliding channel on the other end.

                      If this was mine I would get hold of a good used genuine adapter and cable. I can't say if it will fix your problem, but the level of shock you describe suggests an unsafe situation that needs to be addressed.

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                      • #26
                        Grounded adapter or not I would want to know where in the heck the voltage source is?

                        I mean, come on. A laptop should not zap you.

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                        • #27
                          Agreed.

                          The OP measured 3v, but I was expecting maybe 80v there. It's common to get a tingle off an ungrounded Macbook - some perceive it as a mild shock but this one sounds more severe. A DMM should easily have high enough impedance not to load down the voltage, which can be measured between the metal chassis and earth.

                          In many supplies there's an EMI coupling capacitor which connects from the secondary side of the transformer to the primary side - often at the mains rectifier bridge. This capacitor is responsible for the high voltage elevation on the output. I have seen really cheap supplies where this capacitor connects to mains neutral. The assumption there is that neutral is at or near ground potential - except if the input leads are reversed the connection is to the live side. If the capacitor breaks down then there can be a much higher risk of shock. Often it's just a cheap 1KV resin-dipped ceramic and not a 'class' capacitor.

                          In post #7 it's mentioned there's no shock when on battery, but just re-reading the posts he mentioned earlier that he gets a shock even with the speakers plugged in but switched off - I'm not clear here what's switched off.

                          I would re-check the PSU on its own. Plug it in and measure between each of the output connections and earth, both AC and DC. You have to be certain you're measuring to a known-good earth connection, otherwise you won't get a sensible reading. Please, re-check your reference point for mains earth - either a verified earth pin in your socket, or earthed water pipe. Do the same for you powered speakers if they're running off an adapter. You have a high enough voltage to shock you. This has to be a voltage referenced to earth and I think the 3v you're reading is to something not directly earthed.

                          The guitar amp is grounded, so this needs checking - plug in a guitar lead and measure between the sleeve of the plug and the earth pin of the mains plug. It may read some resistance depending on the amp (it could have an elevated signal ground). If it reads open, try your DMM on the diode check function and see if you have 0.7v.

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                          • #28
                            I change for a apple adapter that i bought 85 €. And it WORKS ! No shock anymore, no hum in the guitar sound even close to the laptop. So for me it's OK.
                            I can record safely.

                            Thanks for the help everyone !

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