ASUS TP412UA GPU or CPU not turning ON

[sikocan]

Hi all this relates to the issue where the computer turns on but nothing else. The only coil not getting power is COIL Numbered 8. I have provided as much details as possible and images as well and also link to the post where initially I thought it's a BIOS problem, maybe it is, the last COIL is not being turned on.

Original post to BIOS with full details are on this link:
https://www.badcaps.net/forum/showthread.php?t=93187

NO Power or Battery os CMOS Battery
COIL Ohms
1 179k
2 5.95
3 8.2
4 58
5 19.17k
6 70k
7 273
8 1.85

DC Jack in Turned Off No Battery
COIL Voltage
1 0
2 0
3 0
4 0.999v
5 3.33
6 5.15
7 0
8 0

DC Jack in Turned On No Battery
COIL Voltage
1 8.4
2 0.94
3 0.78
4 0.997
5 3.33
6 5.15
7 1.2
8 0

COIL 8
Leg left 4.35k
Leg right 3.22

COIL 8's MOSFETS OHM Readings
MOSFET 1
Gate to Source 2.93
Gate to Drain 1.74M
Drain to Source 80K+
MOSFET 2
Gate to Source 4M
Gate to Drain 4M

COIL 8's MOSFETS V DC Jack In Not Turned ON
MOSFET 1
Drain 19.17
Source 0
Gate 0
MOSFET 2
Gate to Source 0
Gate to Drain 0

Power injected to LEG 2 of COIL 8 and middle section of the GPU/CPU gets hot which I suspect is normal as that's where the power is going and connected to.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

More pictures uploaded.

[paulo66]

Re: ASUS TP412UA GPU or CPU not turning ON

Hello, are you sure about the resistance readings re left right legs to ground? Looks like coil 8 might be open.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

Another member on Discord forum of Electronic Repair School, Seeker, pointed out that the Gate to Source on High Side Mosfet 1 is not normal. I pulled them both out, although they work well for example when I put my finger on it to reset, they reset, I apply positive V to gate and Drain and the Drain to Source opens however when I attempt to get Resistance readings it's all random and most times I can not get a reading for both of them and mainly for Source and Gate. I do get readings for Source to Drain in closed position of 2.8M ohms but never a reading for the GS on either of them or Gate to Drain.
I'll have a go at replacing them tomorrow.

COIL 8
Leg left 4.35k - This goes to the Mosfet
Leg right 3.22 - This goes to the CPU/GPU area.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

MOSFET 1 and 2 are reading O.L in 200ohms range for all legs, G>S G>D D>S

Source to gate on the motherboard for MOSFET 1 location is 2.26k

[paulo66]

Re: ASUS TP412UA GPU or CPU not turning ON

Look, a coil is nothing but a piece of enameled wire wrapped around an iron core. So it's basically a short-circuit for DC. The DVM ought to read continuity between both ends of the coil. Measuring their resistance to ground gives the same result as measuring two resistances in parallel. Unless of course there are two distinct grounds.

[paulo66]

Re: ASUS TP412UA GPU or CPU not turning ON

OH I can see now in the first picture, you removed the coil prior to the readings. Sorry if I sounded patronizing.

[paulo66]

Re: ASUS TP412UA GPU or CPU not turning ON

Are there any PWM signals at pins 4 of the fets?

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

Hi Paulo,

I'm sorry I made it look confusing, at time of deciding to take more measurements I had the coil out, I did it put it back. Pin 4 does not have a voltage hence the mosfet not turning on, if it did, MOSFETs would work well as they do outside the circuit. I don't know where this Pin 4 of the MOSFET goes, I'm assuming your pointing to Gate. I don't really want to run a wire source to drain as that would push 19v through from the Drain.

[paulo66]

Re: ASUS TP412UA GPU or CPU not turning ON

Yes, pin 4 = gate. I believe these fets are not being used here where Vin = Vout. Instead, they are switching on and off at very fast rates to convert the 19V at the drain of MOSFET1 to a much lower voltage. The coil reacts to AC, the higher the frequency, or the rate at the voltage changes, the higher the reactance. This AC is a series of pulses. You have to use an oscilloscope or a logic probe to detect their presence. If the pulse trains are arriving at the gates, most likely one or both fets are faulty. If not, maybe there´s a fault in the controller that sends the pulses, or a cut in the tracks or, maybe it´s the BIOS that is not sending the right commands to the controller, or some "EC ready" is not arriving at the controller.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

Hi Paulo, I do have a logic analyser but not sure if it can handle voltage arriving to gate? I assume it's less then 5V? I'll check using logic analser today and take a risk and if it is arriving as you said, and mosfets are not working, then I'll replace them.

This style mosfet is new to me. Maybe before that in continuety mode find out where the gate is going on the board and see if there is a fault there.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

So I figured out that the High Side Gate is connected to Pin 25 of Richtek RT3602AC a triple channel PWM controller with integrated driver for the Mobile CPU Power Supply.

https://datasheetspdf.com/pdf/141224...tek/RT3602AC/1

I'll check with logic analyser today see what's going on.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

I have monitored the activity of the Gate with logic analyser, you are right sir, I did see pulses very very fast but only for a brief time when mosfets were OFF the system. I did replace the 2 mosfets with the exact same model from another laptop and the reaction is same no change. Only 2 options left which I still think it's a BIOS issue No. 1. or worse case is the Richtek RT3602AC which I doubt at this stage as it's a very busy chip and it's doing other things at the same time correctly hence it's able to turn and work with other mosfets in the system.

I have started uploading all my work so far onto Youtube and I'll update the link so you can see and have a better idea. Any other options?

It could even be the onboard RAM but I have no way of knowing how to disable it.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

The video is now live:
https://youtu.be/SCqTQkvmqas

I suspect ram or bios.

[piernov]

Re: ASUS TP412UA GPU or CPU not turning ON

https://logi.wiki/index.php/User:Pie..._I_solve_it.3F

The iGPU core voltage is almost never relevant. It typically only comes up when there's a significant load on the iGPU. It can often be seen spiking a couple of times on the oscilloscope when POSTing.

In other words, it's generally normal that it's missing. If you have some kind of issue with the machine, the cause is most likely elsewhere.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

Then it's the ram last resort.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

I did see the spike/initial working stage using Logic Analyzer, the PWM controller was sending rapid pulses, this happens at turn on time very briefly, not detectable using multi Meter. It's Also in the video.

[piernov]

Re: ASUS TP412UA GPU or CPU not turning ON

If it's not POSTing (caps lock key not triggering caps lock LED for example), I'd try a few BIOS as usual. Not that the vietnamese website is a reliable source but it has a good bunch of dumps.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

I've tried 1 here and 1 of my with cleaning. I've got same model working coming on Wednesday next week, but until then I wish to be able to fix this.

[sikocan]

Re: ASUS TP412UA GPU or CPU not turning ON

Bios flashing fixed. Found one on the net, it worked but 30 sec delay and didn't detect ram. I have fixed those in the attached cleaned me region for others to use.

Bios moved to "Bios requests ONLY!" section - https://www.badcaps.net/forum/showpo...85&postcount=6

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