Toshiba L50-B-16X powering itself on 3s after successful shutdown

[Vspeed]

Hi,

This laptop has a too long history already. I bought it working but with the hinges broken. When I was trying to fix it, pulled the motherboard out and when I was assembling it again, like many people, I plugged the speaker cable in the wrong connector (white one near the ram slots) and killed the CPU.
I then replaced the CPU i7-4500U with a i7-4510U. Cleaned ME and it was working again fine, or so I thought until I installed windows and saw that it was not completely true.

The issue is, when I shut it down, it shuts down normally and if it has the battery or the power adapter or both are attached, it powers itself on again after around 3s. The power button it working fine.
It only stays off if no battery is connected and I pull the power cord right after it shuts down. Then I can plug the power back and it stays off.

The only thing I can think of is some power signal is telling it to turn on again. Could it be that the i7-4500u and i7-4510u have some different power signal pins?

I have another board with the same reference (DABLIDMB8E0 REV:E) but with a 5th generation i5-5200U and around the CPU there are 2 or 3 resistors set in a different configuration

In bios configuration I don't see any enabled option that could cause this behavior.


Edit: Can it be NPCE985LA0DX IC issue?


Thank you.

[mon2]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

You may have a false wake on lane or similar PCIe wake event. Check your removable PCIe based adapters like ethernet / wifi and remove them for further testing.

[Vspeed]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Just did that. Disconnected everything that I could from the motherboard and it's having the same behavior. Could the CPU not be receiving the signal that tells it to turn off?
It doesn't even stays suspended. It immediately wakes up.

Thanks for the reply

[mon2]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Can you link a schematic for this logic board? (or any other silk screen markings)

1) Review the mosfets linked to the charger IC to be sure that they are not leaking.

Remove all power -> measure their resistance across the mosfet pins:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)


Low resistance = defective mosfet. Check the battery mosfet that is used to power the logic board.

Which charger IC is onboard? TI ('BQ') series ?

2) Aside from the above, search for 'WAKE' signals and note their active polarity. That is, WAKE# = will wake up the board if the signal is LOW.

For now, since the adapter (without the battery) works, review the power mosfets.

[Vspeed]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Here is the schematic. I'm not sure it is exactly 100% for this model.
https://drive.google.com/file/d/1V6N...ew?usp=sharing
Can you open it?

source (1-2-3) & drain (5-6-7-8) - Mhoms
source (1-2-3) & gate (4) - 5k ohms
gate (4) & drain (5-6-7-8) - Mhoms

I'm not sure which mosfet is the battery one. Measured PQ16, PQ17 and PQ9.

Board pictures:
https://imgur.com/gallery/SXXAlUf

[mon2]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

source (1-2-3) & gate (4) - 5k ohms

This looks very low and not normal for a working mosfet.

Can you confirm the reading and the meter scale? Or share a pic while taking this measurement of the meter face.

Focus on the attached area of the PCB -> your battery connector is visible and so are the HIGH and LOW side mosfets that are used to charge the battery.

Respectively, the PCB designer will house the charger IC in this area as well. Look around and share closer pictures. The charger IC should be nearby and also the battery mosfet.

Post the TOPSIDE markings of each such mosfet (black / square looking parts). We can then determine if they are N-channel or P-channel (most likely will be N-channel).

So far, unable to find a similar looking PCB / schematic but for now, it does not matter.

[mon2]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Ok - just received your schematic. Thanks.

Attached for future readers.

See attached mosfet area - interested in the voltage at pin # 2 (gate) of PQ3.

PQ3 will be a small 3 pin part (perhaps SOT23 or SC-70 package). You can post close up pics so we can verify.

This gate voltage will decide if the battery mosfet @ PQ5 is ON / OFF to power the logic board. If this part of the circuit is working then PQ5 needs to be reviewed to see if it is defective.

You can check if it is defective by removing all power / no battery and then checking the resistance across PQ5 pins.

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)


Low resistance = defective mosfet

PQ5 = battery mosfet.

[Vspeed]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Hi,
Sorry for taking so long.

I think the markings on the board are different from that schematic.
The components do not match what I see in the board labeled PQ3, PQ5 or PQ9.

edit: Should I measure with the laptop on or off? I ask this, because If I power off and remove all power sources and then connect them back, it stays off. If I power it on and leave them on, it powers up again by itself.
I'll measure some voltages around with it powered off, just the power adapter connected and post new pictures with some measurements.





Hope you can guide me better with these closeups


edit2: here are the measures with just the power adapter connected and laptop powered off.



thank you

[mon2]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Resistance and diode mode checking are always with the power off. Best to remove all power feeds including battery to be sure.

[Vspeed]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

checked all mosfets, specially the SOT-23 ones and found nothing unusual. Lowest resistance was 90kohms. Diode mode readings are normal.
bough another dead board for comparing values, hopefully doesn't have this issue. It has the CPU shorted. All the visible mosfets in the closeup pics read the same values.

[mcplslg123]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Did you desolder the lan chip as @mon2 suggested or only removed the wifi card??

[Vspeed]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Did you desolder the lan chip as @mon2 suggested or only removed the wifi card??

The lan is in a separate board. I disconnected the flat cable to it, yes.

[Vspeed]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Got a fully working board and while comparing, found two mosfets with a low diode reading. They were PQ16 and PQ21, one near the 19V power input, the other near the DVD sata port. After replacing them, the reading got back to same value as the other OK board. Unfortunately the laptop still has the same behavior, powering on itself.
I'm starting to think that the Nuvoton NPCE IC is faulty. Do you think this is a possibility?


Thank you

[mcplslg123]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

Sio fault is very unlikely. I beleive lan chip and wifi card already removed. So suggest to desolder sound and card reader chip and then check again. If the issue persists even after these steps, then you need to focus on dc-dc conversion circuit where ALW is coverted to VS.

[reformatt]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

NBSWON# and DNBSWON# logic lines? There's 2x ESD diodes, D3 and D6, maybe isolate those? SLP_S3# go low when turned off? Schematic posted here is for a AMD CPU, but OP says it was an Intel CPU that was replaced?

[Vspeed]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

NBSWON# and DNBSWON# logic lines? There's 2x ESD diodes, D3 and D6, maybe isolate those? SLP_S3# go low when turned off? Schematic posted here is for a AMD CPU, but OP says it was an Intel CPU that was replaced?

I'll try to check those when I find the time. Yes, I swapped a dead i7-4500 with a i7-4510. I know the schematic is not exactly for the same board but I cannot find one for this exact model.

[Vspeed]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

I just checked those SWON logic lines and SLP_S3 (NPCE pins 95, 94 and 91) and they go low when I shutdown the laptop. They come back high (2.3V, 2.6V 3.3V) when the power LED comes ON again.
Those diodes are not present in the intel motherboard version. The power board doesn't have any diode, just two resistors and the motherboard also doesn't have any diode near the power button connector. I also compared all the diodes against the good board and they read the same values. I was not able to find anything else reading different values.
I must say that the laptop doesn't power on if I disconnect all the power sources and then connect them back. It just does once I power it via the power button and then shut it down or just press the power button to force it to shutdown.
I read somewhere that the CPU might not be receiving the signal to power off so it wakes the computer again.

Your feedback is appreciated.

[Vspeed]

Re: Toshiba L50-B-16X powering itself on 3s after successful shutdown

I just checked those SWON logic lines and SLP_S3 (NPCE pins 95, 94 and 91) and they go low when I shutdown the laptop. They come back high (2.3V, 2.6V 3.3V) when the power LED comes ON again.
Those diodes are not present in the intel motherboard version. The power board doesn't have any diode, just two resistors and the motherboard also doesn't have any diode near the power button connector. I also compared all the diodes against the good board and they read the same values. I was not able to find anything else reading different values.
I must say that the laptop doesn't power on if I disconnect all the power sources and then connect them back. It just does once I power it via the power button and then shut it down or just press the power button to force it to shutdown.
I read somewhere that the CPU might not be receiving the signal to power off so it wakes the computer again.

Your feedback is appreciated.

I was measuring the wrong points. Here are the correct measures and finds.
All SWON points go low when I press the power button and the laptop turns off, same as the good board.
I measured some other points that I think might be interesting. They are:
11 - TP ON OFF
15 - VRON
16 - MAINON
22 - SUSON
26 - S5_ON
27 - DISPON
73 - SLP_S5 (always 3.3V both boards)

They all go low, except DISPON that once the laptop is powered for the first time, it remains high even after pressing the power button.
The test board sets this signal low.