T460s no power

[Kad009]

Hi hope everyone is well
This is my first post sorry if I miss anything let me know
I have a T460s which shows no lights and does not power on there is 19.6v on the main power rail
The ethernet port lights flash
I reprogrammed bios no luck
thanks in advance

[mon2]

Hello and welcome.

There are few fuses onboard - be sure to check if they are blown or not. Remove all power. Meter in diode mode. Short your meter probes and there will be a tone beep. Touch the probes across each of the fuses to confirm if they are ok or are blown.

Do you have a voltage @ VREGIN20 side ? Connect your adapter, meter in DC volts scale of 30v or higher -> measure the voltage to ground on each side of the fuse(s). This will also confirm if the fuse(s) are blown or not. Red meter probe on the fuse; black meter probe to ground (metal shield is ok on the logic board). Proceed with caution since the board is (partially) alive.

[Kad009]

The first picture is the closest fuse to the input jack so I think that it is DC_PWR20_F
It has continuity and 20v both sides
The second two are by the battery connectors they both have continuity but no voltage on either side
I can't seem to find DOCK_DCIN20

[dudz622]

check also if 5 volts,3 volts and 1.8 volts are present

[Kad009]

I can only find 0.9
I'm not sure really to look i looked by the coils and keyboard connector
when I plug the charger in I get 0.1v at the Ethernet and power button light and they flash
sorry I'm not so experienced

[mon2]

Ok - believe I finally have the proper schematic that matches the silk screening showing in your posted pics.

See attached. Locate the current sense resistor and carefully measure if you can read ~20v to ground. Ground is the large copper area of the logic board.

Red meter probe on the resistor; black meter probe on the copper area. Meter should be in 30V or higher DC volts scale. This check will confirm that the power path is ok up to here before it reaches the battery charger @ U1 = BQ24780S.

After the above check -> locate the square black chip with a 'BQ' topside marking and then share pics of this region. We need to check if the power path is ok at this charger IC.

[Kad009]

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

[Kad009]

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

[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]

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

[Kad009]

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

[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 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

[Kad009]

here

[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]

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]

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]

Oh my bad thank you for clearing that up

[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]

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