ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

[alb3rt121]

At the beginning, as a new user, he would like to welcome the group of forum users. I hope you will help.

The topic concerns
Model: Asus TUF Gaming FX505DT
Platform: FX505DD rev 2.0
Processor: Ryzen 5 3550H YM3500C4T4MFG
Graphics: Nvidia GTX 1650 N18P-G0-A1
KBC: IT8987E
BIOS chip: MX25U12873

In the laptop, after connecting the power supply, only the keyboard is illuminated.
No reaction to the switch, no diodes light, no battery charging.

Current consumption after applying voltage 0.04A without frames and batteries. Slightly warm CPU.

In my opinion, coils without description have good resistance to ground, so I did not select it.
Transistors checked. No short circuits.

What else can I check? Please note that I do not have extensive experience in repairing plates.
Greetings.

[Stevedb]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Can you toggle capslock on extern keyboard?

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Unfortunately, I don't have a keyboard now.
On another forum I was told that the CPU might be damaged

[Stevedb]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Or you can use an usb mouse or usbstick too or internal keyboard. If it doesn't react then it is probably bios issue.

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

The voltage on the USB port is not present. I checked in the diagram where the control signal for the power transistor comes from. It comes with the CPU

[Stevedb]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

The i would try to flash bios but make sure you keep your original dump. I would try first to clean me region of your original dump.

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

I have already flashed the bios from Asus website once. Without result.

I also noticed that pressing the ON button causes the voltage on the IT 107 leg to drop from 3.5V to 3.2V

[mcplslg123]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

If it's not turning on, just follow basic steps to diagnose. Start with dc-in mosfets, check the voltage on gate(pin4) of mosfet, then proceed to check whether +19V is present on CLR. If yes, then proceed to 3V/5V PWM ic and check whether +3V LDO/+5V LDO is present or not. If +3V LDO is not present, your kbc is not powered, so it'll remain dead.

Update us about the findings.

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Measurement

CLR +19v- Present
LDO +3v - Not preset. I can't find where it comes from

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

I found a pwm controller.
Measurements in the attachment

[mcplslg123]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Measurement

CLR +19v- Present
LDO +3v - Not preset. I can't find where it comes from

Pin3 of RT6575B is your 3V LDO. Going by your measurements, its present.

[mcplslg123]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Current consumption after applying voltage 0.04A without frames and batteries. Slightly warm CPU.

Is your dc supply 3 digit or 4 digit?? If it's 3 digit, then consumption is 40mA-so something must be slightly hot.As per your observation, its cpu which is getting hot-not a good sign.

Measure resistance on each and evry coil .

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

My power supply is 4 digit (0.000). After put voltage to motherboard 0.045A
The measurements are in the attachment.

Coil at CMOS battery - 122 ohms. I forgot to add in the photo

[mcplslg123]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Locate the dc-dc converter ic for +3V/+5V to +3VS/+5VS and check resistance on ALW as well VS side of this converter. Something is not hot?? Consumption at 45mA is abnormal in standby. I doubt mb is perhaps partially switching as u got kbd backlit which is not powered by ALW rail.

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

The CPU is slightly warm, as I said, but not hot.
I will check the converters as soon as I can. I will let you know about the results.
I would like to know why there is a low resistance of 0.9 ohm on the GPU power supply. This is normal?

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

You mean + 3VSUS + 5VSUS?

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Can such symptoms be caused by a damaged SIO?
I noticed that on IT there is no 3.3V on legs 11, 83.

[mon2]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Unable to locate the schematic for the FX505DD but have the FX505DU in the (paid) locked database.

1) Is FX505DU similar to your logic board ?

2) Are you using the recommended 150W power supply ?

3) Remove all power. Meter in resistance mode.

Check if the first 2 mosfets are damaged or not with resistance checks.

Meter in 2k scale (or similar).

Check the resistance of:

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


Post the readings. Checking for low resistance readings = defective mosfet.

Check both of the first 2 mosfets - see attached.

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

Thank You for help.

1. The schematic of the Fx505DU is the closest to the DD.
2. I use oryginał 150W power sipply.

I will let you know when I take the measurements.

I am attaching the diagram of the FX505DU board

[alb3rt121]

Re: ASUS Tuf Fx505dd rev2. Does not start up, does not charge the battery.

I just found out how MOSFET works using diode and resistance mode. lol. By the way, I found a MOSFET with a low resistance between G and S. This is the VVT and DDR power supply (I don't know what VVT is) After the measurements, it turned out that the U8300A chip
RT8231BGQW legs 16, 17 are mosfet controlled. The IC didn't look very good, it had changed color like burnt. I have ordered parts so I will reply soon. May it work.