Lenovo M70Q not booting

[Chura]

I have M70q thinkcentre, that went our of warranty 3 months back, and as expected, its dead now.
nothing happens when I press power button, tried different power supply, nothing.
how can I troubleshoot capacitors or what so ever ?

[mon2]

Hello and welcome. It figures.

Start with the power path at the DCin power connector. Meter in DC volts mode (30v or higher is ok). Measure the voltage to ground at the PL203 or other ferrite beads. What is the measurement?

We are only checking if the physical connector is ok to power this motherboard.

The MAIN power adapter connector appears to be JDCIN4 in the schematic.

[Chura]

Thanks for your reply!
Its showing 20V, all capacitors positive side showing 20v. Also PL201/2/3 the same.

[mon2]

Check if you have this voltage on pin # 7 of PU201. Measure with care since the board is being powered.

[Chura]

Yellow measure 0v, not sure if its because my needle won't touch. orange should be fine ? also 0v

[mon2]

Yes, orange is fine. That is a fan out PCB trace that mates with the same contact on this semiconductor. Even the inductor above the orange circle is fine for this measurement.

[Chura]

Yes, orange is fine. That is a fan out PCB trace that mates with the same contact on this semiconductor. Even the inductor above the orange circle is fine for this measurement.

Its all 0v
and the VIN (ping #15) has 20v
so this is the fault ? I read its a " USB Power-Distribution Switches" what its role ? can I replace it at home easily ?

[mon2]

What is the voltage to ground on pin # 9? This is the enable pin for this USB load switch. If this is a logic '1' = high; then the switch is enabled otherwise the switch is disabled.

Check if there is a shorted part on this rail. Remove all power. Meter in resistance mode. Measure the resistance with one meter probe on pin # 7, other meter probe to ground (metal shield is ok).

[mon2]

Found this:

Lenovo ideacentre AIO 3-24IMB05 won't turn on • VLab

[Chura]

What is the voltage to ground on pin # 9? This is the enable pin for this USB load switch. If this is a logic '1' = high; then the switch is enabled otherwise the switch is disabled.

Check if there is a shorted part on this rail. Remove all power. Meter in resistance mode. Measure the resistance with one meter probe on pin # 7, other meter probe to ground (metal shield is ok).

Pin 9 is getting 3.3v
resistance of pin 7 to gnd is 00.7

[Chura]

Found this:

Lenovo ideacentre AIO 3-24IMB05 won't turn on • VLab

Indeed I get short between ping 7 and gnd, I guess its not suppose to
now, how can I identify which SMD cause that ?

[mon2]

Correct There should not be a short on this rail.

Based on the other post about the same fault, guessing the issue is with a shorted cap.

There are a few methods:

1) inject a low voltage (1 volt should be enough; not higher) onto this rail and check who heats up with a thermal camera or using IPA (pharmacy alcohol) - the IPA will evaporate faster on the heated part

2) use a milli-ohm meter and check the resistance to ground of each part on this rail.

3) remove parts to locate the shorted one - every part on this rail is a suspect.

Let us try option # 3 - flux and remove PC218 and / or PC219. Then test if the resistance is higher or not after the process. If the resistance remains the same, solder these parts back. Be sure to not create a solder short in the process. You will need flux + tweezers + hot air tools to properly remove and replace the parts.

If the short is still present, remove PC213.