T460s no power

[Kad009]

I read that cpu coils have very low resistance to ground. Is it that low?

[Kad009]

L32 to ground 19 ohms
L29 to ground 10 ohms
L30 to ground 9 ohms
In diode mode, all the coils beep to ground

[mon2]

50 Kohms up to 1.5 Mohms

This is all that matters. You do not have a short on this power rail. Continue to test in the same way, each and every inductor on the board. Checking for a low resistance reading.

[Kad009]

I read that the multimeter applies a very low voltage and then calculates the voltage drop, thus calculating the resistance, which charges the capacitors, therefore varying the resistance. I'm not sure if that is correct. I read that on Reddit. Please correct me if I am wrong

[Kad009]

I'm a bit confused
on both my multimeters one probe on ground and the other probe one either side of the L5 coil the resistance keeps changing starting at 50 Kohms up to 1.5 Mohms

[mon2]

Remove all power -> meter in resistance mode -> measure the resistance to ground of the L5 inductor. We are only checking if there is a short on this line. Proceed to check each and every inductor using the same process (always without power). If checking resistor or DIODE mode -> never any power to the board.

Post each measurement and the units of measure which for resistance will be ohms; kohms (thousands of ohms); Mohms (mega-ohms), etc.

[Kad009]

on TPS51285BRUK pin 3(VREG3) reads 3.3v
and pin 13 (VREG5) reads 5v

[Kad009]

So what I think is L5 I circled in red and on both sides I read 0.2v
I don't know if this helps but the input of the mosfet I circled in blue reads 19.6 and the output and gate read 0v

[Kad009]

Oh my bad thank you for clearing that up

[mon2]

Someone is guilty of causing this board to not power on. We are only checking each power rail for the suspects. Each power rail has a local inductor / local current sense circuit. If the current draw is too high (due to a shorted part on the rail) - then that power rail will turn off to ideally prevent damage. This stops the board from booting. Each inductor (often grey in color and will be with 2 leads) should be checked for a voltage. Compare the voltage against the schematics. If in doubt, power down and check the resistance to ground of that same inductor. Some low voltage rails are expected to be low in resistance to ground and that is by design. For example the CPU rail will be a low resistance to ground. Hoping we find that the root cause is a shorted capacitor which is quite common. A shorted capacitor will cause an excessive current draw and power down the board.

[Kad009]

Ok I will check and let you know I'm currently not able to
But correct me if I'm wrong obviously you are miles ahead of me in experience and knowledge
Shouldn't we be trying to get the board to power on then dealing with the battery just my 2 cents

[mon2]

ACOK read 3.18v
VCC3SW 3.28v

These are good measurements. The charger IC is ok with your power adapter and has raised the ACOK flag to a logic of '1'= ~3v. No issue here.

If the battery is attached to the board, measure the voltage to ground on inductor @ L5 (either side is ok on this part). What is the voltage measurement?

Each similar inductor on the board should be measured to check which voltage is present on each coil (inductor). Each inductor is linked to a power rail which accepts the ~20V which we know is present from the external power adapter and lowers it to a suitable voltage = buck regulator style.

[Kad009]

here

[Kad009]

I have no idea what is going in your explanation (due to my inexperience and knowlegde)
ACOK read 3.18v
VCC3SW 3.28v
The picture below is where I tested (VCC3SW) correct me if I am wrong
and the voltages could have a millivolt difference

[mon2]

Ideally the meter should be accurate but let us confirm if the charger IC believes the ACDET to be enough or not.

Check the voltage to ground of ACOK signal @ pin # 5 on the same charger IC (U1). Note that the VCC3SW must be present for this signal line to be a logic '1' state.

Share the measurements of the voltage to ground of the ACOK pin #5 and also the VCC3SW rail. Measure where it is convenient.

ACOK is an open drain pin when the logic state is true. If the charger IC is ok with the ACDET pin voltage then ACOK will be a floating pin (like an open switch). Only then the VCC3SW will pull-up this floating pin state using the resistor R2349. At that point the transistor / mosfet at Q181 will enable and drive the signal line ~EXTPWR to a low state (will be a '1' state otherwise).

That is, when ~EXTPWR is a logic '0', then the logic board believes a suitable external power adapter is connected to the board.

[Kad009]

I don't think my multimeter is perfectly accurate
so it could be above 2.4v

[Kad009]

my bad i checked that already but never mentioned it pin 6(ACDET) = 2.35V

[mon2]

Good. Carefully measure the voltage to ground of pin 6 (ACDET) on the charger ic. It may be easier to check at the resistors that also connect to pin 6. We are wanting to confirm the ACDET voltage is high enough for the charger to proceed. If your probes are not suitable then do not continue and we can do other tests.

[Kad009]

on pin 28(vcc) of Q24780SRUY I read 19.58v

[Kad009]

That is the first thing I checked I got 19.6v
Here is the picture you requested