Advice on Lenovo S400 Ideapad no display

[Askic]

Hello guys,

I need a bit of advice how to proceed in trying to repair my own Lenovo IdeaPad S400 Intel i3 3rd gen laptop with Intel integrated Graphics HD 4000.

First of all the exact same situation already happened once before. The laptop just lost picture, like the display is off, but LEDs are working on the laptop (there is one LED around power button). After shutting down (10 s pressed power button), and trying to power on again the following is happening:
- charging LED is ON.
- when power button is pressed, LED button is ON
- fan starts to spin for a few sec and then stops, while computer remains ON
- there is a heat on CPU heatsink and there is a heat on the chipset or GPU (not sure what is it).
- no POST sounds at all

First time this problem appeared, I opened back cover and start measuring voltages. There were voltages present on all big inductor coils. And while I was doing measurements, picture on the display appeared.

The laptop worked fine for a few weeks and last night the exact same problem happened again.

Main rail power as well as 3.3V, 5V and CPU power are present (CPU is getting hot). I can turn on/off the laptop on the power button. When connected to the external display, there is no picture, so laptop in reality doesn't start. First indication is FAN which stop spinning after few seconds even if CPU get real hot 1 or 2 minutes later.

I have tried to exchange the RAM module with known good working one, but that was not the cause.
I suspect that problem is GPU, but not really sure how to prove that.

Do you have any similar experience?
What would be your advice?

[mcplslg123]

Re: Advice on Lenovo S400 Ideapad no display

Take the motherboard out of casing and look for corrossion under microscope/magnifying glass.

[Askic]

Re: Advice on Lenovo S400 Ideapad no display

Take the motherboard out of casing and look for corrossion under microscope/magnifying glass.

By measuring different voltages, I have found that only +VGFX_CORE is missing, but on this forum, on a similar question for Asus laptop, I have found out that this voltage is missing also if there is a BIOS/SPI rom fault.

What is even more strange is that by measuring on different coils and caps, laptop cam back to life. Not once but twice. I was not able to reproduce and find out exactly what I need to press/ push in order to bring it to life.

After shut down or even reboot the problem reappears.
PL 302 produce 2.2V but that is cell voltage for battery, and I guess that is OK.

I managed to measure all other voltages: 20.5V, 5V, 3.3V, 1.5V, 1.8V, 1.0 V(CPU core). On PL902 there is nothing and that is where VGFX_CORE (GPU voltage I guess) is created.

[mon2]

Re: Advice on Lenovo S400 Ideapad no display

Remove the battery and check the laptop. The unit should function without a battery.

Or..is the combination of the adapter & battery required to boot?

Does this laptop use a type c power adapter or the standard coax connector?

[Askic]

Re: Advice on Lenovo S400 Ideapad no display

It is an old laptop from 2014. Doesn't have USB-C ports. Adapter is classical 2 pin 20V.

By closer visual inspection I have found out that is missing PQ903, but it seems it maybe from factory. Anyway it doesn't prevent it to come to life occasionally when "doing something" on the back or measuring random voltages. PQ903 is on the CPU line and that voltage is present.

Very strange issue. There was no liquid damage and I cannot see traces of corrosion anywhere.

Battery is removed all the time.

[Askic]

Re: Advice on Lenovo S400 Ideapad no display

Update after a few more test.
I have placed a completely new SSD and tried a few times. After I disconnected the power adapter and returned battery after cca 3 min after power ON, picture suddenly appeared on the display and FAN started to spin normally. I have installed win 10 and perform a few tests install all drivers, restarted many times. However, after first shutdown (through start menu). The problem is present again. This laptop has integrated Intel GPU, so it is not possible that this is faulty (like cases where people heat GPU in order to make it work).

Really don't know what I can try next. When the laptop is in this mode, not even Caps Look LED works

[Adenitz]

Re: Advice on Lenovo S400 Ideapad no display

Schau mal:
https://youtu.be/113BEhBX8kA

[Askic]

Re: Advice on Lenovo S400 Ideapad no display

Yea, I have seen such videos, but usually CMOS battery cannot cause this. Anyway it is 3.18V, but I tested just in case (had to cut off one leg since battery is a small one soldered, not standard CR2032).

What I found very interesting is I have a voltage drop over PL401, which shouldn't be the case, one one side I have stable 3.3V, but on other side voltage fluctuates, usually it is about 2.55V, but can go up to 5V and even once I saw 6 V. Inductor coil is a short circuit for DC current, so voltage drop across it should be zero, bu it is not the case. I have checked this a couple of times.

Please have a look at the attachment.

[mcplslg123]

Re: Advice on Lenovo S400 Ideapad no display

With a multimeter, it often shows different voltage readings on both sides of coil. Its always the output side which will measure differently every time. this is normal due to current draw. You can measure with DSO and it will show a perfect 3.3V on both sides with different pwm pulse.

[Adenitz]

Re: Advice on Lenovo S400 Ideapad no display

With a multimeter, it often shows different voltage readings on both sides of coil. Its always the output side which will measure differently every time. this is normal due to current draw. You can measure with DSO and it will show a perfect 3.3V on both sides with different pwm pulse.

I didn‘t know that. I would expect that output side have stable voltage reading on multimeter because after coil usually there are filter caps. I would expect fluctuations on the input side (mosfets side) because there are very high frequency voltage changes.
Anyway if the problem is not solved by cmos battery replacement, then most likely is either Bios od even RAM slot. I have seen in the scematics that this model has only one slot.

Good luck, I hope you‘ll be able to fix it.

[Sephir0th]

Re: Advice on Lenovo S400 Ideapad no display

This would be new for me too. Maybe just a mispell by mcplslg123, since it is usually the buck converter side which often can't be catched by some multimeter.

However, I'd go for detailed visual inspection under microscope. Look for loose connection of ribbons/connectors and of course cold solder joints, corrosion, and so on. Maybe you're lucky because the alternatives probably wouldn't be good news.

[mcplslg123]

Re: Advice on Lenovo S400 Ideapad no display

This would be new for me too. Maybe just a mispell by mcplslg123, since it is usually the buck converter side which often can't be catched by some multimeter.

However, I'd go for detailed visual inspection under microscope. Look for loose connection of ribbons/connectors and of course cold solder joints, corrosion, and so on. Maybe you're lucky because the alternatives probably wouldn't be good news.

Sorry. I meant what you typed.

[Askic]

Re: Advice on Lenovo S400 Ideapad no display

Thank you guys for your valuable inputs, I really appreciate it.I am really interested to learn what could be a reason for this. In 1 out of 10 tries, laptop just starts working by itself after running in this no display no POST state for about 5 to 10 minutes. Motherboard graphics is UMA so there is no separate GPU chip that is dying. The only explanation would be a cold solder joint, but in that case I‘d be able to make it work by pressing different parts of the board which is not the case. Same thing happened about a month or two ago but once laptop came back to life, it worked for weeks.
I don‘t have a microscope but have good magnifying glass and cannot spot anything out of order.

[Stevedb]

Re: Advice on Lenovo S400 Ideapad no display

I would do a clean me regiin of your bios image

[Askic]

Re: Advice on Lenovo S400 Ideapad no display

I would do a clean me regiin of your bios image

Just an update on this issue. It seems that problem is solved by writing new BIOS.

Fist of all, the board has two chips, U44 and U46. One is BIOS, other is EC.
In the first attempt, only new BIOS is written to the BIOS chip, and problem seemed solved. Laptop immediately returned back to life.
However, after 2 or 3 hours, it reappeared while loading the windows. Picture just dissipated and the screen shut itself. The problem was back.
After that both EC and BIOS are written, but this time a new chip was soldered on the board (from donor board, similar but not exact).
Now, it passed more that 10 days of everyday use and it is working OK, so I consider this solved.

I still don't understand how corrupted BIOS can have intermittent behavior, just to laptop sometimes just wakes up randomly.

Anyway, thank you all for your valuable suggestions.