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11-21-2019

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WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-21, 22:19 PM

I have a type 20M9 Thinkpad P52 which works great. However I have encountered a small issue with the WiFi indicator light that is staying very dimmly lit after shutdown. This adds a very small but noticable battery drain when the machine is off the grid. All of the indicator lights work nominally when the machine is powered on. Latest drivers, BIOS and W10 updates are installed. This happenes both on battery and plugged in. This is the only indicator light on which this occurs. The light goes away afer reconnecting the battery ( plugging out and in). 

 

I am suspecting a software bug since the issue goes away after reinserting the battery but still I do not exclude a possibility of a small hardware issue. 

 

 

Has anyone got information about this and if not I would like to submit it as a fault for future reference.

 

I have attached a photo taken with night mode on so do bear in mind that in reality the led appears less bright than on the picture. 

 

 

 

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409 Posts

07-08-2019

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Re: WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-23, 5:01 AM
Hi!
I have noticed this, but I assumed it was just persistence from the white phosphor of the LED...

I have a few ideas why it could stay dimly lit, but it should not! I'll need to check if my P52 has the exact same issue, and open a ticket if it does.

Martin

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Re: WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-23, 22:14 PM

 wrote:
.....

I have a few ideas why it could stay dimly lit, but it should not!.....
Martin

 

 

Hm, what are you thinking of?

 

Thanks for your response, Martin. 

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Re: WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-24, 0:10 AM

Hi Wusten,

The electronics guy in me thinks that there might be a powered-down gate back-fed from a still-powered part of the circuit. In some instances, protection diodes can power a device in unusual ways. When that happens, you get power in places that are expected to be unpowered. Here is an example: EEVblog #831 - Power A Micro With No Power Pin!

 

Since the LED is very dim, my guess is that some gate stays activated (latched?) until some electrical charge drops very low. One way to test would be to turn off Wi-Fi just before turning off the machine. If the LED is off after off, that is a valid clue about residual power discharging. Unfortunately, it would require a schematic or a circuit analysis to solve the mystery! And no, I don't have a P52 I want to disassemble for the analysis ;-)

 

I checked my machine once after unplugging it and the LED was off. That covers only one scenario from maybe 10...

 

Martin

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Re: WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-25, 6:31 AM
I'm replying to myself to add:
- If I turn the machine OFF (Wi-Fi ON) plugged in, the LED is faint;
- Then if I unplug the machine it turns OFF.
- Plug it back in and it turns back faint.
- Wait some "long" time and it's OFF.

So, it looks like the external power enables residual power to discharge through the LED. The fact that it's completely off a while later seems to indicate it's not connected to battery power, else it should be of constant brightness. Also, I disconnected my system for a few days and my battery did not visibly discharge.

I wonder if it could be linked to some Wireless Wake-On-LAN feature. Keep the card ready to wake the machine if plugged in, but disable if unplugged? I know the WLAN card is vPro capable, and WWOL is available for vPro machines.

Martin

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6 Posts

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Re: WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-26, 10:44 AM

Appreciate the response as always, Martin. 

 

My machine doesnt seem to follow the same pattern. No matter what I do, it stays dimmly on when shut down/in sleep. It only goes away when I remove and reconnect the battery. I run fast startup setting on, but the issue persists even when it is off. 

 

I did test the battery drain overnight and it definitely is connected to this, it drains 2-5%, compared to when I reinsert the battery after shutdown resulting in 1% or no drain. 

 

It's not a major issue but surely should be clarified/investigated further. Can you point me in the right direction of contacting support/making a ticket?

 

Also if you've got any ideas about what I should test, please do tell. 

 

Thanks!

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Re: WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-26, 20:03 PM

Hi Wusten,

I suspect it might have something to do with both firmware and software. I used BIOS 1.29/EC 1.15 and everything that Lenovo Vantage Enterprise recommended was installed when I ran the tests.

 

Today, my BIOS was updated to 1.31 and a few drivers where installed, so I will need to test again to verify.

 

One main thing you should check is that Wake-on-Lan is disabled in BIOS (IIRC, if it's there). If enabled, that would keep networking adapters in stand-by in case the system admin wants to boot it up. Not a good idea on a laptop in a carry-case ;-). Another place to check is in Device Manager, for the network adapters, disable "Allow this device to wake the computer":

Disabling this setting for both the LAN and Wi-Fi adapters should reduce the power consumption when OFF. Now, there is a bug in the LAN driver, you MUST also disable "Wake on Link settings (else the previous setting is ignored according to the release notes):

One last setting that might influence the OFF power consumption is in the BIOS, and it's about allowing charging from USB when the computer is off. For charging to work, the port must be able to detect something is plugged in, and my guess is that uses power even if nothing is plugged in.

 

Now, to submit a support request, go to https://pcsupport.lenovo.com/, go to your machine's support page, and look for the "Contact Us" section on the left or bottom of the page. The support options specific to your machine will be displayed.

 

Martin

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134 Posts

11-12-2019

IL

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Re: WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-27, 0:38 AM

My guess: this is a combination of a slightly leaky transistor, residual charge in capacitors and a MOSFET that's staying on when it should be off (might be linked to vPro as ve2mrx suggested). Regardless, if a low-power LED stays barely lit, we are probably speaking about power consumption of no more than 15 mWh (and I'd think much less). To drain a 90 Wh battery this way would take 6000 hours. Of course, we do not know for sure whether additional circuitry stays powered when not supposed to as well.

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Re: WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-27, 1:13 AM

Just for the kicks, I measured power consumed by a low-power laptop LED when it's slightly lit. That turns out to be around 3mWh at most (my instruments are not precise enough for such a small current so I'm giving the higher limit of the estimate). So a 90Wh battery would power this LED for 30000 hours.

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Re: WiFi indicator light stays partially lit after shutdown [Thinkpad P52]

2019-11-27, 1:25 AM
Hi ThinkpadIL,
That is the main reason I suspect something else is consuming power in "shutdown" like Wake-On-Lan or something. A very dim LED, even white, should not consume enough power overnight to lose a few percent of battery.

Windows 10 being a mish-mash of tablet, PC and phone OSs makes it complicated to find the ONE setting to fix this. I, by far, prefer the classic Control-Panel. The rest looks like baby stuff to me. ;-)

Maybe the powercfg command could help somehow?

Martin

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Also, 2x M820z, 1x P520c, 1x ideaCentre 300S-11IBR

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