thinkpad motherboard flaw : can I power it from DC on battery connector - Page 1
Forum section: electronics / repair

author: pbig
author_rank: Newbie
timestamp: March 25, 2023, 03:53:22 pm
content: Hi,I am Pierre, live in France and have met a problem with a laptop Thinkpad L480 series from Lenovo. From what I have found on the net, many laptop (L480/L580) fitted with the same NM461 motherbard meet the same problem : the USB-C suddenly fails and either you simply lose DC power or the connector burns, probably due to corrosion even without spillage.I met the worst case : using a microscope we have seen that under the protective resin layer, copper tracks have melt and I can no longer power the laptop from this USB C PD port. I think it is a general flaw for this series and do not want to spend/waste money on new mobo that has not been repaired.. since I think all will fail.In my case, the battery is has not been charged since it happened and the ouput voltage is now 0 so I cannot charge it and test the motherboard. Do you think I could remove the 11.1V/45Wh battery and power the laptop directly from a DC power supply (buck from/12V for example) through this connector ? Is this risky ?All advices will be greatly appreciated. Regards,Pierre

author: khaahk
author_rank: Contributor
timestamp: March 25, 2023, 07:50:11 pm
content: You have another usb-c port at the docking connector, try to use it, might be working.

author: zilp
author_rank: Frequent Contributor
timestamp: March 25, 2023, 08:24:32 pm
content: Now, I have no experience with that particular model, but I have powered an older thinkpad with a power supply through the battery port in the past, that worked perfectly fine. Also, based on the voltage, I suppose that this is a 3S LiIon pack? In that case, 12V without any further regulator should be fine, the max charge voltage for LiIon is usually 4.2V, so a fully charged 3S pack would be at 12.6V.Also, potentially you can charge the battery just fine by simply applying (current-limited) voltage to the terminals? Chances are that only the discharge transistor in the pack is switched off to prevent deep discharge, but the charge transistors is still switched on. Just be careful with not overcharging the pack, of course ... though probably the controller in the pack would prevent that, too.

author: pbig
author_rank: Newbie
timestamp: March 25, 2023, 10:20:50 pm
content: thank you zilp, I will try this. The battery pack is a 3cell one, I have remove the black tape around it to access the cells and gave them individually a voltage boost. Thanks to the protection, the voltage has not gone under 2.4V - I measured at the cells - and it has climbed up to 4V with a shitty lab power supply (doesnot give a constant current). I will try tomorrow a fresh start from the battery and if successful will take the chance to find a solution with a 12V power supply.All the best to you from France.

author: pbig
author_rank: Newbie
timestamp: March 26, 2023, 09:14:15 am
content: thanks again Silp,the laptop has started on battery so nothing vital was destroyed on the battery power circuit. I will then try the fix with a 12V DC power supply. How many Amps are needed? the original PS give 65W (3.2A/19.5V) but if I don't need to charge the battery, I can reduce current needs.

author: zilp
author_rank: Frequent Contributor
timestamp: March 26, 2023, 04:49:02 pm
content: > the laptop has started on batteryThen you could also check whether there is voltage at the battery terminals when it's not plugged into the laptop. If so, then obviously the laptop can deal with voltage on those pins without any further negotiation or stuff. (I'd be surprised if it couldn't, though).> How many Amps are needed? the original PS give 65W (3.2A/19.5V) but if I don't need to charge the battery, I can reduce current needs.Yeah, you certainly don't need that much, and also depends on peripherals, of course--if you don't use the USB ports to power stuff that draws a lot of power, then you don't need to supply that power to the laptop either.Your battery should be measuring power draw when discharging, and that information is usually exposed through ACPI or something, so the easiest approach would be to just connect all the peripherals you want to use, put full load on the CPU and possibly GPU, max out screen brightness, and then just look at what the battery is measuring, that should give you a good idea of how much power your PSU needs to be able to provide.

author: alm
author_rank: Super Contributor
timestamp: March 26, 2023, 04:58:41 pm
content: If you plan to run it by replacing a battery with a power supply, then I would put a large cap at the output of the power supply, because the laptop may well be using the battery as a smoothing cap to deal with peak current draw. The average power will probably be well below 65W, but modern CPUs are very bursty loads, so it wouldn't surprise me if it could reach or even exceed 65W for a few seconds at a time under certain circumstances (high CPU / GPU load, external USB devices attached drawing a lot of power).

author: Koray
author_rank: Regular Contributor
timestamp: March 26, 2023, 05:02:36 pm
content: Have you tried using the other USB-C port next to the main (broken) one, as suggested by khaahk? There are two USB-C connectors with two separate power circuits as far as I know. See the attached photo.K.

author: pbig
author_rank: Newbie
timestamp: March 26, 2023, 08:13:13 pm
content: I have charged the Li Ion cells individually up to 3.86V - because I cannot easily access to the battery pins or motherboard (too small for a correct contact with my tips)- but as soon as I turn the laptop on with its battery, after the beep it displays 0190 critical battery error and turns off. I measure with the multimeter the battery voltage -laptop off- I get 11.0V that would explain the error but it is incoherent with 3*3.86~11.5V when cells are connected in serial. Is the voltage drop usual ?I have tried to increase the battery cells charge : at 4.0V the cell still sucks ~0.5A so I may be far from complete charge or the protection circuit also has a flaw.Answer to Koray and khaahk : I have connected the USB-C power supply of my Dell Latitude to the second -unburnt - USB C connector. The laptop doesnot start : that would indicate me that if it has the power delivery functionality, it probably shares some of the circuitry with the first - damaged - one.Thanks again for you answers.

author: alm
author_rank: Super Contributor
timestamp: March 26, 2023, 08:32:09 pm
content: Quote from: pbig on March 26, 2023, 08:13:13 pmI have a T480s (probably very similar motherboard) without damage to the USB-C connectors, and it will charge the battery from either connector, though I have not checked if it will boot with a charger in the second USB-C port and a flat battery.

author: pbig
author_rank: Newbie
timestamp: March 27, 2023, 06:30:02 am
content: hello,I have successfully increased the battery charge and the laptop boots fine now. No longer displays the 0190 critical battery error at POST. Since the battery protection circuit stopped the current from external PS when the battery is full, I will probably solder cables directly on the board with an external connector to a 12V PS (with a large capacitor). When I find the Lenovo PS, I will check using the second USB-C connector but I have strong doubts it still accepts charge. I thank everyone for kind suggestions.Have a nice day wherever you are.Pierre

author: testpoint1
author_rank: Frequent Contributor
timestamp: March 29, 2023, 04:01:12 am
content: according the type C recommendation, used for laptop, it will use 19V, so you can try to connect a fixed 19V DC.

author: pbig
author_rank: Newbie
timestamp: March 31, 2023, 07:43:07 pm
content: hello testpoint1,I would be glad if I could connect this laptop to the USBC port but, unfortunately, this is the one that burnt and the second one - still working - doesnot accept input power/Power Delivery. Since for me the only way to power this laptop is to use either a battery (nominal output 11.1- nominal input 12.6V) either a DC power supply. Logically, it should operate correctly in the same voltage range as the battery so that the laptop accepts this as a valid substitute.