Lenovo YOGA 900

[sauce]

Hi,

I have a dead motherboard of a Lenovo YOGA 900-13ISK (NM-A411)

Does anyone know if a NM-A921 is fully compatible (for a YOGA 900-13ISK2) ?

Everything seems the same except a more recent CPU.

Thanks.

[sauce]

Re: Lenovo YOGA 900

Hi,

So i found a dead motherboard for my model.
With this motherboard the fans spin but black screen.

I do not have the EDP_VDD_EN_R voltage. CPU / GPU dead ? How to be sure all others voltages are present.

[SMDFlea]

Re: Lenovo YOGA 900

Hi,

So i found a dead motherboard for my model.
With this motherboard the fans spin but black screen.

I do not have the EDP_VDD_EN_R voltage. CPU / GPU dead ? How to be sure all others voltages are present.

Check voltages on all large grey coils. Search the forum for the schematic, and look for a power sequence or power block and test all voltages to see whats missing

[sauce]

Re: Lenovo YOGA 900

It seems I have not checked GFX_CORE I will try to check it.

I have the schematic.

[sauce]

Re: Lenovo YOGA 900

So here are the voltages of coils near CPU :

PL16 : 0.902VDC
PL25: 1.09VDC
PL26: 0VDC
PL29: 0VDC
PL27: 0.97VDC

So no GFX_CORE.
What could I test after that ?

[Sephir0th]

Re: Lenovo YOGA 900

You can ignore GFX_CORE since it will only show up under load. If the display circuit still doesn't get enables, I'd proceed with a known good BIOS, also check resistance to GND of EDP_VDD_EN_R. If you're out of luck you're dealing with a bad PCH failing in the late sequence here.

[sauce]

Re: Lenovo YOGA 900

EDP_VDD_EN_R to GND is 66k

Just replace ISL95857HRZ because it was the only common thing and now GFX_CORE is 0.480VDC.

But still no display

[Sephir0th]

Re: Lenovo YOGA 900

It is not normal that you can catch voltage at GFX_CORE so if you can (always) measure voltage there now, I really have to assume you made the issue worse. Since you decided to go the random way instead of following what was advised I also cannot assist here anymore.

Good luck

[sauce]

Re: Lenovo YOGA 900

Sorry but I replaced the chip before I read your message

[Sephir0th]

Re: Lenovo YOGA 900

That's another story then and sorry for my rude comment.

If the board deasserts PLT_RST# is usually a good indicator whether it is should be ready to P.O.S.T., ruling out a corrupted BIOS is the next logical step then.

Do you trust 100% in your soldering of the VRM controller?

[sauce]

Re: Lenovo YOGA 900

I think I will resolder the VRM controller it was quite hard to solder

CPU core is still 1V.

Just test the bios CHIP of the donor board no success the fans not spin at all.
I resolder the original the fans spin.

Tomorrow I will try to resolder this VRM controller and I will tell you...

[mcplslg123]

Re: Lenovo YOGA 900

In my experience, if gfx core remains constant readable voltage on SOC platforms, its bad cpu.

[sauce]

Re: Lenovo YOGA 900

Ok even if I have the caps lock that works ?

[Sephir0th]

Re: Lenovo YOGA 900

No, when Capslock LED responds (on external Keyboard) the board does indeed the P.O.S.T.
You're troubleshooting "just" a no picture issue from here.

[sauce]

Re: Lenovo YOGA 900

I do not have the tools to program bios

But i with donor bios it does not work (no fan spin) and when i put original it works (fan spin, caps lock ok...), does it mean the bios is ok ?

[sauce]

Re: Lenovo YOGA 900

Just another question does screen needs to be plugged to test EDP_VDD_EN_R ?

[mcplslg123]

Re: Lenovo YOGA 900

Ok even if I have the caps lock that works ?

Of course not

[sauce]

Re: Lenovo YOGA 900

Anyone knows if Fn+R method to flash bios works on this model ?
And what is the bios name to put on USB drive ?

[sauce]

Re: Lenovo YOGA 900

I managed to program the bios with my rasperry pi but still fan spin and no display.

I have no more ideas

[Sephir0th]

Re: Lenovo YOGA 900

As we had already told: when CapsLock is reacting the BIOS should be fine and you´re challenging a "no-display" issue then. i think nobody suggested to mess with the BIOS so i don´t know what you try to archieve here.
you should put the original dump back to the motherboard and take a closer look to the voltages at the display connector, so enables, 19V, 3.3V and so on. Or even better: take the board to a serious repair shop.