Lenovo Ideapad3 NM-C821 faulty motherboard

[nrj1982]

Hello all,

I have a Lenovo Ideapad3 laptop, that has recently stopped working. When pressing the power button, the led is going on, but nothing else is happening.

I have checked the 3.3V, 5V and 20V - all of them seem present (checked with multimeter and oscilloscope in order to verify that they are stable).
I have checked the voltages around PU1901 - 0.9V, 1.8V, 5V, 2.5v, 0.6V and 1.2V - all of them are present.

Now going further in the debug, I found that the CPU voltages produced by RT3662AC (PU5901) PWM driver are missing. I can see that the 20V are present on PQ5901.

Now I have tested the procedure described in the RT3662AC datasheet, where we have:

I can see the pulse on the EN pin, and the VDD, but PGOOD remains 0, and of course the UGATE is also 0. That is why I am starting to think that the RT3662AC is faulty.

Do you think that there is something else that I can test, before trying to replace the IC? The 0.8Vref from the RT3662AC are present, but looking at the datasheet diagram, this voltage is produced from another part of the IC.

Thanks in advance,
Mitko

[nrj1982]

Some update:
- I saw that there is a very low impedance between the drain and source of PQ5905 (and all MOSFETs connected between the VDDC and GND), around 2.1 ohms.
1. Removed the RT3662AC - still the short is present;
2. Removed all MOSFETs (PQ5902, PQ5903, PQ5905, PQ5906, PQ5908), the short is still present;

Is it possible that the CPU is dead?

Thanks,
Mitko

[reformatt]

2 ohms seems ok to me. What about VDDCR_SOC voltage? That needs to be there first as your main Vcore rails are under control of the APU via the SVID interface.

Lenovo's usually suffer bad balls under the CPU due to the poor quality solder they use. If the fault occurred without any liquid damage or corrosion, this would be my first suspect.

[nrj1982]

2 ohms seems ok to me. What about VDDCR_SOC voltage? That needs to be there first as your main Vcore rails are under control of the APU via the SVID interface.

Lenovo's usually suffer bad balls under the CPU due to the poor quality solder they use. If the fault occurred without any liquid damage or corrosion, this would be my first suspect.

Hi reformatt,

In fact, there is no liquid damage or corrosion. Initially I have started looking for something death, because when I opened the laptop, there were two screws, free rolling over the motherboard, so I was thinking that they made some king of a short. Those two guys were coming from the SSD support.

I can not check the VDDCR_SOC voltage for the moment, because I have removed couple of components (including the RT3662AC), but during the weenkend I will try to add them back. I will keep the post updated with this.

Regarding the Lenovo BGA problem, now I am starting to thing that I am facing exactly the same issue, and I suppose that this will end with the very same problem, but let's first check all the other possibilities.

Thanks you for the help.
Mitko