Electronics > Repair

thinkpad motherboard flaw : can I power it from DC on battery connector

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pbig:
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

khaahk:
You have another usb-c port at the docking connector, try to use it, might be working.

zilp:
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.

pbig:
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.

pbig:
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.

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