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Lenovo Adapter Customer Sent It Back To Me

By on December 10, 2020
how to repair lenovo laptop power adapter









Lenovo Adapter which I have repaired 2 days ago comes back with another problem. Customer stating when he touches back side of the laptop he gets Electric shocks.

Just discussed with the customer for proper earthing in his premises where he uses laptop. He told me that he is having three desktops and two laptops on same location but none of them having this issue. So I request him to send me back the adapter with the laptop. On arrival of laptop and adapter I connected both and powered mains and with line tester I just touched screw side and tester lights up…..

lenovo power adapter repair

Further I reopened the adapter for testing what is wrong in side I missed something or what??……

On visual inspection I found …..How I skip this point??? Guess what??………There is no Earthing wire connected by the manufacturer on adapter’s mains socket side…….

lenovo power adapter socket

how to fix laptop power adapter lenovo

Checked Laptop with another compatible adapter it does not give shock.

That means laptop is ok & confirmed problem with adapter only. Need some Views from your side how to solve this shock problem …………………….

Second thing I found when I am reading reference voltages on adapter it shows

laptop power adapter specification

Outer Body of the DC Pin is –ve

Inside Body wall is + 20V & Center Pin is Signal……..

lenovo power adapter signals

On testing with multimeter I found 10KΩ Reading between Center pin to ground In 65 watt laptop adapter.

third wire in lenovo power adapter

Other side On the PCB I found only two wires that is +ve & -ve…no third wire

3rd wire in lenovo power adapter

So I am bit confused from where it gets signal????………….I have measured the center pin voltage it does not show any voltage but it works perfectly on the laptop.

On Google I found in some adapter centre pin and Ground pin both are connected internally using some value resister. I found in dell adapter this center pin wire is connected to one programmable chip on the PCB in the adapter …

lenovo power adapter schematic diagram

Found this dell laptop adapters are having proper three wire connected on the PCB with proper one to one connectivity from PCB to DC PIN.

lenovo power adapter circuit schematic diagram

Here is datasheet link:

This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.

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Note: You can check his previous repair articles in the link below:




  1. Parasuraman S

    December 10, 2020 at 5:42 pm

    Sorry, I am confused! Have you solved the problem or awaiting a solution?

    • Yogesh Panchal

      December 11, 2020 at 12:45 am

      Still Waiting for solution and suggestion Because many peoples facing this problem in Dell ,Lenovo,HP they called it "Tingle current"
      sharing link for your reference...

      • Basudeb De

        September 26, 2021 at 12:09 pm

        Check the healthyness of the capacitors provided in its filter ckt.Also check the harmonic s content in the DC out put by ossilloscope.Choosing the values of Propercapacitor in the filter circuits . Defects may be rectified.

  2. Arunkant Pandit

    December 10, 2020 at 6:05 pm

    Dear Yogesh,
    Capacitor CY1 connected between hot side ground and cold side ground may be leaky. This can give shock in smps power supply.

    • Yogesh Panchal

      December 11, 2020 at 1:16 am

      Arunkant Pandit,

      Sir, Thanks for your reply but shard circuit diagram is of Dell Charger and case study is of lenovo charger & it doesn't have Capacitor connected CY1.

    • Jens T. Balslev

      January 24, 2021 at 5:53 am

      Hi. Laptop manufacturer may use the sense pin (resistor) to sense a specific supply. I.e. same brand may provide big/small power supplies with same plug!. Then laptop can detect if correct power supply is connected - and if the resistor represent a too weak psu, then the laptop will come with a warning and perform lower.
      Wrt 50Hz-shock, try swap live(phase) and neutral(return) to feel if the shocking become less? If so - then it can be the cross capacitor as mentioned earlier -or leaking debris across the transformer barrier -or worse- the insulation in the switching transformer/barrier is degrated due to exposure to ESD voltages (lightening) when it was in use. A short high peak between primary and secondary side may toast the capacitor and/or the insulation barrier - without making the supply non-functional! That can be tested by proper high voltage testing equiment. But I doubt the cost of a new powersupply can justify many hours of reserach in finding the cause in a broken laptop supply. But interesting if there is an easy way to save it.

      • Jens T. Balslev

        January 24, 2021 at 6:14 am

        One thing more... on many supplies, the mains noise filtering use two high voltage capacitors (typical 5nF/5kV). Each from live and from neutral to the earth pin. But if such filter is in your lenovo supply and the earth pin is not connected, then the voltage on the 'earth' on the laptop's ground will be divided by the two capacitors - so you may have 115vAV on the laptop - independent if you swap live and neutral. Just my cent.

  3. Paris Azis

    December 10, 2020 at 6:19 pm

    Hello Yogesh
    In order to give you a hand on this problem, just tell me if the above schematic represents the power supply with the problem you referred to. I already see a design fault on it...

    • Yogesh Panchal

      December 11, 2020 at 1:19 am


      No---- schematic is just for reference for Dell Laptop Charger and this case study is of Lenovo Charger.
      Even in Dell ,HP laptops also this type of problems found.

      • Paris Azis

        December 11, 2020 at 5:16 pm


        If we take as reference this schematic, the problem is caused by CV1, which (theoretically) couples the primary side ground with the secondary ground.
        This coupling is used for noise suppression purposes. Usually the string of these high Ohmic value resistors connected in parallel with CV1 is omitted in ordinary designs.
        The problem occurs because the "ground" of the primary side is real ground only if it is connected to the neutral side of the mains.
        When connected to the phase, the entire "ground" circuit carries the phase and this is the answer to your question "where this signal comments from".
        Now, the easy way to avoid the bad design result, is simple. When plugging the mains plug and you see the problem with the phase detecting screw driver, simply, reverse the plug's position on the wall outlet.
        Your customer should be advised to do the same. He can mark the correct plug position and keep it always the same.
        If this solves his problem, then there is nothing more for me to say. If not, you need to modify the circuit and make the ground terminal active. But we'll see about that latter on.

        • Yogesh Panchal

          December 11, 2020 at 8:14 pm

          Paris i had already tried inter changing Live and Neutral but no success.
          One thing i have noticed few dell adapters have given earthing wire connected directly on secondary side DC pin Out Ground.

          • Paris Azis

            December 12, 2020 at 5:47 pm

            Yogesh, can you please tell me what is the A.C voltage level at the wall outlet you used to power and test this power supply, if you measure a) across the phase and ground conductors and b) across phase and neutral conductors? (With the outlet free of course, i.e. nothing connected to it).
            I am asking you that because interchanging Live and Neutral MUST have an effect. Here is why:
            Having as reference the above schematic (which doesn't differ from the most cheap designs), this noise suppression capacitor is always connected as shown therein.
            It is clear therefore that one end of it is connected to the minus side of the bulk capacitor (primary circuit ground), while the other end of that cap is connected to the secondary ground (ground to ground coupling).
            Therefore, under normal conditions, if the Live is connected so that it appears on the plus side of the bulk capacitor, this means that the primary side ground is effectively grounded through the neutral conductor. In turn, the secondary ground circuit will be safe.
            These cheap designs use the circuit ground as safety ground, but this is absolutely wrong. This is exactly what happens in your case and ideally needs a modification.

            • Yogesh Panchal

              December 21, 2020 at 3:35 pm

              Our wall outlet is 230V AC, Line to earth showing 230V & Neutral to earth showing 0V..

              What modification you suggest?

        • Paris Azis

          December 11, 2020 at 8:39 pm

          Correction for above comment:"where this signal comes from"...

  4. AdamS

    December 10, 2020 at 6:20 pm

    It may well be that, with nothing connected, the charger 'sees' the 10kOhm resistance between the centre pin and 0V and uses this to set itself to some sort of 'standby' mode, where the output is switched off. Then, when you connect the laptop, it will 'see' different resistance which then activates the output.

    As to the missing earth pin, this is not unexpected. As the case of the charger is plastic, it is a Class II Double Insulated item and so no safety earth is necessary. The fact that it is passing a higher voltage into the laptop and causing shocks means that there is most likely a problem inside it somewhere.

    • Yogesh Panchal

      December 11, 2020 at 1:23 am

      You are absolutely right but here in this adapter nothing is connected to center pin there is only two wires in the adapter +ve and Ground.

  5. Albert van Bemmelen

    December 10, 2020 at 8:06 pm

    I was about mentioning the missing Earth connection but AdamS already nicely did by saying: "As the case of the charger is plastic, it is a Class II Double Insulated item and so no safety earth is necessary".
    Still in case of desktop (or tower-) powered computers, the Earth wire can cause a problem, even if it always is connected. Because in my living room none of the power wall outlets are Earthed! Which means that the integrated AC input filters (through two capacitors) in the Power Supply units provide an about 220 VAC low current voltage to the metal case of these metal cased computers. Like it probably is in the case of this repair article if the Earth wire on the power wall outlets is not connected. It even happened once or twice a year that the Earth safety breaker fuse in my Living room suddenly switched off the 230 VAC power because most of my devices carried a floating high voltage through their AC power inlet filters to the not connected Earth line. And this Earth safety wire is most important to preventing from getting electrocuted when taking a shower! (Why all metal water pipes need to be Earthed!).

    • Yogesh Panchal

      December 11, 2020 at 1:25 am

      Majority all the brands having same problem in some of their series i have found this problem in hp,dell,lenovo In customer forum criteria on their website.

  6. Jeffrey Thomas Narrazo

    December 10, 2020 at 10:01 pm

    If you encounter hot ground on a laptop adapter there might be some leakage current passing thru usually ceramic filter capacitor. in some cases if there is metallic shielding check for damage insulation but most good quality adapters run fine without the grounding pin physically connected to ground.

  7. Henrique J. G. Ulbrich

    December 11, 2020 at 1:24 am

    I have a lot of doubts: 1) have you concluded the maintenance? 2) What does the word Signal mean in this case (Signal for me is information being processed, nothing to do with power supplies)? What is the purpose of IC DS2501? according to the diagram, it has one input and no output! (i.e., it connects nothing to no one else...) 3) Doubts concerning R40 (no value informed in circuit diagram): What is its purpose? Perhaps current sensing for a current limiter circuit, but this is not evident in the circuit; 4) CY1 can have problems, as stated Arunkant Pandit. Anyhow, the way CY1 is connected compromises the desirable galvanic isolation, that's a characteristic of SPMSs.

    • Yogesh Panchal

      December 11, 2020 at 2:22 pm

      Henrique J. G. Ulbrich,

      1) It is not yet concluded yet just waiting for the feedback.
      2) Sir, circuit diagram is not my concern which i shared for reference.
      in dell DS2501 is programmable IC which send information to Laptop Bios
      that 65W adapter is connected and charging voltage is released to
      Battery Charging Circuit.
      In Dell Adapter you find 12.5V to 14V on center Pin.)
      3) This circuit Diagram is just for reference.

  8. Yogesh Panchal

    December 11, 2020 at 1:31 am

    Jeffrey Thomas Narrazo,

    You are right i have repaired many adapters without earthing wire but they work fine.this adapter doesn't have any metallic shielding.
    Thanks! for reply.

  9. maurice

    December 11, 2020 at 2:17 am

    Is this an original part of an aftermarkt cheap China part? You would think that original Lenovo would use the extra pin

    • Yogesh Panchal

      December 11, 2020 at 2:38 pm


      This adapter is Original Adapter supplied with the laptop, Need your expert advice for the same why center pin does not have any connection on the PCB though it shows reading of 10K ohms respect to the ground ? this is what discussion about.
      thanks! for reply

  10. Anil Varma

    December 11, 2020 at 4:50 pm

    Connect a wire from mains Earth pin to secondary Ground pin, this should solve the electric shock. Change the CY1 capacitor that may be leaky the resistance parallel to CY1 is not required only a Class Y safety capacitor is sufficient.
    If changing CY1 not solve your problem then the transformer coils may be touching each other (primary and secondary) .

  11. Yogesh Panchal

    December 11, 2020 at 8:56 pm

    Anil Varma,

    Thanks! for your comment...I think your first point should work.

  12. Humberto

    December 16, 2020 at 1:20 pm

    Wow! I had never seened this with the Earthing pin.

    • Yogesh Panchal

      December 20, 2020 at 11:02 pm

      I was also exclaimed.......Lol

  13. lj

    January 29, 2021 at 12:11 am

    it looks like a fake lenovo charger usually sold at around usd5
    i would avoid using them

  14. steve allen

    February 23, 2023 at 12:38 am

    I designed a DC-DC switch mode power supply using the LT8337-1 from ADI. I needed a very quiet (EMI) power supply to power my T420 from a 12.8 LiFePO4 battery. I cut the connector off the Lenovo original AC power supply (90W) and there is no third wire. The center pin is unconnected. This is a stock Lenovo power supply. My assumption is that this connector was standardized on by Lenovo for the T4xx series laptops thinking they would have the need to communicate between the laptop and the power supply. Obviously later on in the production run Lenovo realized this was an added cost (three wires verse two wires) so they opted on only using two wires. I see no difference in laptop performance using any of my Lenovo power supplies or my designed DC-DC switcher.


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