Lenovo Yoga 300 - motherboard troubleshoot - Page 1
Forum section: electronics / repair

author: Libas
author_rank: Regular Contributor
timestamp: October 10, 2022, 09:34:04 am
content: Hi, could you please help me to clarify following issues?Lenovo Yoga 300-11IBYModel name 80M0S/N P20044EB1) What component is used to supply power to power button + BIOS chip during power OFF phase (just charger plugged in, laptop OFF, 3.3V power supply switched OFF). Some schematic available?2) Verify following measured voltages on main power rail. Is such a reduced voltage normal (with charger plugged in) or is it sign of failure?8V charger pluged in + battery connected - MOSFET Q15 not fully opened as I would expect (50%duty sine, cca 40kHz)6V only charger pluged in (battery disconnected) - MOSFET Q15 not fully opened as I would expect7.3V only battery inserted (charger unplugged) - Q15 fully opened

author: Libas
author_rank: Regular Contributor
timestamp: October 10, 2022, 09:35:00 am
content: Charging port + Q15 in top right corner of board

author: Libas
author_rank: Regular Contributor
timestamp: October 10, 2022, 01:42:30 pm
content: anybody able to identify this component? (datasheet).Very probably driver 3.3/5V I guess...but I dont know how to find datasheet.Marking:EN=2AT1L

author: florentbr
author_rank: Contributor
timestamp: October 10, 2022, 02:45:58 pm
content: > 6V only charger pluged in (battery disconnected)Isn't the charger supposed to deliver around 19v ?> What component is used to supply power to power button + BIOS chip during power OFF phase (just charger plugged in, laptop OFF, 3.3V power supply switched OFF).It should be U6 on your image.It's a Richtek RT8205MGQW dual step-down controller with 3.5v and 5v LDO.

author: Libas
author_rank: Regular Contributor
timestamp: October 10, 2022, 02:59:30 pm
content: Quote from: florentbr on October 10, 2022, 02:45:58 pmYes true...it delivers 19V but as I see on the scope transistor is for some reason not fully opened and I can see some switching activity. Does anybody have similar experience?

author: florentbr
author_rank: Contributor
timestamp: October 10, 2022, 03:17:27 pm
content: The voltages you measures are the battery rail and not the main rail.Q15 and Q31 and part of the DC to DC converter to convert the 19v from the charger to the battery voltage.What's wrong with the laptop?

author: Libas
author_rank: Regular Contributor
timestamp: October 10, 2022, 06:51:00 pm
content: Quote from: florentbr on October 10, 2022, 03:17:27 pmI measured this voltage on all power supplies on the board so I dont think it was just a battery rail. I didnt find 19V anywhere on the board.Troubles with laptop were following:-Main symptom was automatical switching ON/OFF....right after lid opening. After some period (around 10s) it switched OFF.-Switching frequency was faster with charger plugged in.-When started without charger I noticed that LED was blinking orange (which means battery less than 5%) but that was not true....battery was nearly full.-Sometimes I was able to break this ON/OFF loop with chaotic pressing of power button. Laptop was running fine without any load but after some load applied (I guess) it shutted down.-When charger was plugged in LED was solid white and I noticed some regular interrupts for a milisecond (like some driver restarting)....this looks OK now.-Symptom above was not correct. Those interrupts are still present. But as manual says...it should be "slow blinking"...which signalizes battery 20-80% and still charging. Instead of this slow blinking there are those fast interrupts. The same happens when battery is 2-20%...just colour of LED is amber.Of course I have measured nearly zero voltage on power button. During my investigation I was probing with power supply on various places looking for any short. After this probing (probably after probing on power button) I noticed there is already correct voltage on the power button so everything looks to be OK now.But Im not pretty sure with that low voltage on power rail. Its still without heatsink so I didnt try to load it yet.Tried to assemble it and load it...everything looks to work fine instead of that charging LED blinking.

author: florentbr
author_rank: Contributor
timestamp: October 10, 2022, 08:35:03 pm
content: The voltage on the main rail is supposed to be:Charger plugged: charger voltage, around 19vCharger unplugged: battery voltage, around 7.4VIf you don't get the 19v when the charger is plugged, then there's something wrong.If you follow the traces, the charger DC IN should supply the RT8205MGQW through two back to back mosfets.When the charger is unplugged, a third mosfet is supposed to connect the battery rail to the main rail.> When started without charger I noticed that LED was blinking orange (which means battery less than 5%) but that was not true....battery was nearly full.Given the symptoms, it's possible that one of the rail is taking more current than it should.Maybe a half shorted capacitor.

author: Libas
author_rank: Regular Contributor
timestamp: October 12, 2022, 02:37:43 pm
content: I have troubles to find datasheet for IC 8782LN...any help? (second photo top right...U14...next to the charging port)

author: florentbr
author_rank: Contributor
timestamp: October 12, 2022, 03:23:55 pm
content: Looks like there's no a public datasheet for this 8782LN QFN-24.The pinout is provided by some schematics:https://www.badcaps.net/forum/showthread.php?t=72808

author: Libas
author_rank: Regular Contributor
timestamp: October 12, 2022, 05:48:58 pm
content: Quote from: florentbr on October 12, 2022, 03:23:55 pmgreat...thanks!