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Lenovo T460 Power On Draws 0.10 amps

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    #1

    Lenovo T460 Power On Draws 0.10 amps

    Hi guys have two Identical Lenovo T460 that came to me with LEd Power Lights up. 5 seconds fan spin then off. all basic voltages are present.19v,5v,3v, 1.3v memory voltage also. As soon as i plug the charger it draws 0.10 amps and stays there.The both of them does the same thing. No signs of water damage on neither of the boards.Been working on it back and forth for 2 months.I tried different bios but the same thing happens. I notice i have no CPU core voltage and i picked up on an apparent short on VCCGFXCORE_I . Was hoping you guys can confirm for me it is indeed a short or maybe low resistance? I did inject a maximum of 0.8V on that line and it draws 0.8V and 0.11 amps .I removed all the caps on that line and it still seems shorted.It drew 0.8v and 0.22 amps. Resistance Measurements on that line are 3.8 ohms.So just before i give up hoping you guys can confirm the CPU/Graphics might be dead on these boards. Thanks
    I have attached boardview and and schematic in case you may want to have a look.

    Attached Files
    Last edited by platinumsteel; 06-24-2021, 12:19 PM.
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    #2
    Re: Lenovo T460 Power On Draws 0.10 amps

    VCCGFXCORE with onboard cpu will show very low resistance. GFXcore will come last when the mb posts-so vcccore must come before gfxcore. Your problem is missing vcore and not gfx. Check whether you have pch power 1.05V. Ram requirement needs to be checked. 1.8V rail must be present. Give feedback about these steps and then we'll follow.

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      #3
      Re: Lenovo T460 Power On Draws 0.10 amps

      Thanks a lot for giving some hope. I will try to continue working on it thanks. will get back if i come up with anything.

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        #4
        Re: Lenovo T460 Power On Draws 0.10 amps

        Ok mcplslg123 here are some of the results i did so far.Hope the picture of the block diagram helps.I will post a picture below. So i have PCH Power 1.8VS coming out of PCH.Ram rail is up and fully working 1.3V .And also 1.8v rail is present RT8068A .
        Please let me know if there is any more rails i should check. thank you. Presently i ordered the NCP81208 IC which is a voltage regulator for VCCCPU core and VCCGFXCORE as i recently learnt i could be wrong.It should be here in 1 week or so.

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          #5
          Re: Lenovo T460 Power On Draws 0.10 amps

          Readings seems good so far but still u should check all the rails mentioned on Pg13 to Pg 16(SYSTEM POWER MANAGEMENT/CPU POWER). 81208 IC will enable 81380/81/82 which you have correctly understood. It could be a simple bios issue as well so do try flashing new bios with clean me. You can ask for bios in "Bios Section". Else, lets wait till the new IC arrives but i dont think it is defective.

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            #6
            Re: Lenovo T460 Power On Draws 0.10 amps

            Well I agree with you to be honest. Because I had previously thought 81381 and 81382 could of been my issue and ordered new chips and already replaced those chips and nothing changed. The only changes i notice are when i try different bios bins for this model. 2 out of the 6 bios files i tried gives me a 2 second Power LED blink interval and system keep powering on and off almost like if it is trying to start up but can't .That is the state the both labtops came to me with... And the other bios which i have on it now gives me solid LED power light. 3 seconds fan spin and stop and draws 0.11 amps. And ofcourse no cpu vcore. The other bios just knocks out my 3v and 5v rails and doesn't power on. But as u said NCP81208 Regulator might not be defective and yes i too think it might not be bad. So if it doesn't do anything when i put it in.I will buy a working board and then when i get it i'll compare voltages and everything and truly see what's up.

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              #7
              Re: Lenovo T460 Power On Draws 0.10 amps

              Hi again mcplslg123 . I stumbled upon something today and am not sure if it means anything or relavent.When u told me to check SYSTEM POWER MANAGEMENT/CPU POWER . Around U58 which is the CPU.If you notice on U73 I have VCC3M which is 3.3V but on Pin 4 there is 0V . and pin 2 which i believe is the enable pin not sure also has 0V . Can you please have a look and tell me if i that component is really supposed to be outputting voltage? Thanks

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                #8
                Re: Lenovo T460 Power On Draws 0.10 amps

                U73 is related to PLTRST. This signal is among the last to comeup when mb posts.Since your mb is not posting, you can ignore PLTRST for now. This signal will comeup, once mb starts posting. So, nothing unusual here.

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