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5 Posts

12-23-2019

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Yoga C940 power delivery interrupted when using any source other than direct from power adapter

2020-01-31, 16:10 PM

Yesterday I posted about the C2G docking station that Lenovo sells as compatible with the C940 (that's C2G Part# 28845).  Today I'm back with another USB hub with power delivery that has the same results.  This one is the Configear USB-C Hub from Amazon.

 

Both of these USB-C / thunderbolt hubs will charge the laptop after first being plugged in.  That power delivery stops any time that A/C power is disconnected and then reconnected, or when the laptop reboots, and/or the laptop enters a low power state where it does not require the same power delivery (e.g. hibernation) and then resumes normal operation.  C2G technical support has no explanation for this, nor does Lenovo Premium tech support, nor any other technical support resource.  The only way to restore power delivery is to physically swap the thunderbolt port that's receiving the USB hub, but even that does not consistently resolve the power delivery connection.  It is also worth noting that while the power delivery fails, other connections via the hub work (mouse, keyboard, bluetooth headset, ethernet, etc.).

 

Lenovo support suggested they could have someone come out and swap the motherboard, but I suspect this is some kind of firmware issue.  If you have a C940 and have had success consistently charging from a USB hub it would be great to hear about which hub your'e using.

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379 Posts

11-04-2019

PH

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Re: Yoga C940 power delivery interrupted when using any source other than direct from power adapter

2020-02-04, 13:56 PM

Hi ,

 

Regarding the issue, Based on Lenovo's Accessories and Options Compatibility Matrix the only Docking Station that works with the Yoga C940-15IRH(#81TE) and Yoga C940-14IIL(#81Q9) is a ThinkPad Thunderbolt  3 Dock Gen 2. Other branded docking stations are not guaranteed to work. Consult with Lenovo's Accessories and Options Compatibility Matrix if you want to buy any accessories for your device to avoid incompatible devices.

 

Hope this helps and let us know how it goes,

Jeremy



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Re: Yoga C940 power delivery interrupted when using any source other than direct from power adapter

2020-02-04, 15:24 PM

Thanks Jeremy at Lenovo.

 

For whatever reason, Lenovo Premium Technical Support is not aware of your suggestion about the suggested docking station.  I'm frankly a bit shocked that Lenovo only guarantees compatibility with a ~$400 docking station solution.  Would definitely appreciate an explanation as to why every other USB hub I've tried will not successfully resume power delivery to the laptop unless the thunderbolt cable is unplugged and then swapped to the other port on the machine.  Seems like an issue with the machine frimware and/or hardware and not with every USB hub made.

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5 Posts

12-23-2019

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Re: Yoga C940 power delivery interrupted when using any source other than direct from power adapter

2020-02-05, 18:39 PM

@Jeremy_lenovo,

 

Wanted to show the devices that appear based on searching for "hub" in the Accessories tab for my C940.  The link you sent landed me with some crazy spreadsheet that was uninterprable to a consumer.  That spreadsheet looks like an internal-facing support document for Lenovo employees.

 

Anyway, I'd like to reiterate based on the Accessories page I found above and my own experience that I'm not convinced the C940 is for some reason built to only work with a $400 hub brick.  The only thing that consistently fails is power delivery following power supply interruption.  Power delivery is usually restored after swapping the USB-C / thunderbolt input.

 

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Re: Yoga C940 power delivery interrupted when using any source other than direct from power adapter

2020-02-05, 20:49 PM

 ,

 

Cell J2 shows Yoga C940-15IRH(#81TE) and Cell O2 shows Yoga C940-14IIL(#81Q9)) - It has an X mark on Cell J882 and O882 meaning it's compatible and fully functional unless stated. This list is updated once Lenovo's R&D gets another accesory compatible with a model. There isn't really any Docking station made for Ideapads but Lenovo tries to make updates on the computer to make accesories not compatible with it initially to work.

 

 

 

 

I am not saying that other docks will not work but "Other branded docking stations are not guaranteed to work". Other people have made other docking stations to work by doing workarounds. 

 

Regards,

 

Jeremy



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02-06-2020

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  • Message 6 of 9

Re: Yoga C940 power delivery interrupted when using any source other than direct from power adapter

2020-02-06, 8:19 AM

I have a C940 also, and just 2 days ago purchased a UGreen USB-C hub/adapter with PD.   I can confirm that going to standby, and out, charging still works, and unplugging from wall socket and replugging, charging also still works.  Charging speed seems to be the same as plugging directly to the stock power supply (using stock power supply with the hub as well).

 

I purchased this at a small shop in my city's IT mall.  Below is the exact model hub I have, although mine does not have the 2 mandarin characters next to the name on top.  USB3.0 and network connections tested and work fine after power state change as well, have not yet tested card readers or HDMI connections though.

https://shopee.co.th/UGREEN-USB-C-USB3-1-TYPE-C-HUB-8-%E0%B9%83%E0%B8%99-1-USB-HUB-All-in-One-USB-C-to-HDMI-Card-Reader-LAN-PD-Charging-Adapter-4K-%E0%B8%A3%E0%B8%B8%E0%B9%88%E0%B8%99-50538-i.10822.1728988076?gclid=EAIaIQobChMInYaHr7y85wIVShOPCh14cAltEAQYAiABEgJkPfD_BwE

I was able to get it for 1600 baht after negotiating.

This C940 is from Lenovo Thailand with Thai keyboard.   C940-14IL, Model 81Q9

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1 Posts

02-06-2020

AU

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  • Message 7 of 9

Re: Yoga C940 power delivery interrupted when using any source other than direct from power adapter

2020-02-06, 12:50 PM

I have a C940. I just purchased the Lenovo Thunderbolt 3 gen 2 dock. I was happily charging the laptop via the rear thunderbolt port on the dock to the left side thunderbolt port on the C940 and all was fine. I then installed the firmware updates to the dock and applied this from the same left port of the C940. After restarting the machine I now find the left thunderbolt port on the C940 now no longer recognises the dock for charging (I can still charge to this port direct from power supply without the dock).

 

I connected the dock to the right thunderbolt port on the C940 and this does charge the laptop through the dock.

 

I'm led to believe that the firmware update that was applied from the C940 to the dock somehow caused the port on the C940 to stop functioning from a charging perspective but not sure why. I'd like to know how to reactivate it so I can charge through this port (via the dock) again.

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02-06-2020

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  • Message 8 of 9

Re: Yoga C940 power delivery interrupted when using any source other than direct from power adapter

2020-02-06, 13:10 PM

Hearing this, I will not be updating any firmware any time soon....

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1 Posts

04-15-2020

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  • Message 9 of 9

Re:Yoga C940 power delivery interrupted when using any source other than direct from power adapter

2020-04-15, 16:15 PM

We have 3 C 930's and 3 C940's and a total of 5 docs. All of the C940's behave exactly as you've stated in your post regardless of dock computer combination.. Of course I keep the drivers and firmware up to date. However the issue does not exist on the C930's at all. 

 

Hopefully someone will get some help out of this. 

 

As a work around I have put a plug here label on the thunderbolt 3 port that allows charging. It should also be noted that you can not use the dock and a charging cable at the same time the system (at least with my 3 C940's will not charge with to cables that are both hot. 

 

So for now we are stuck just using the front Thunderbolt port with the Docks. Really would like a fix. It is an expensive Dock it should work as advertised. 

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