ASUS UX360UA Turns On No Image

[CohenC]

Hiya,

I'm trying to delve into the world of electronics repair, this forum has been of great help in my research to date, but today I am here with a question of my own.

I've been given an ASUS UX360UA to work on, the laptop powers on and charges, the keyboard 'lock' keys respond correctly and the USB port receives power, however, the OS does not seem to load up as I get no HDMI output or sound when I plug in the USB. I also see no obvious thermal mass through a Seek CompactPro.

I've taken measurements off of the motherboard and found that one of the coils near the CPU reads zero voltage and is shorted to ground, along with all of the capacitors nearby.



Being an ASUS there are no schematics or board view available and this is my first time working on a laptop without them; I'm a bit unsure of where to look next, the board has almost no traces on the top and the entire bottom of the board is just traces.

Any pointers would be much appreciated

[stingerchamp]

Re: ASUS UX360UA Turns On No Image

Hi,

Seems bios issue as no Volt on pin 5,6

If you have oscilloscope
Check pin 5,6

Flash a good known bios

Core coil will always show short to ground as less ohm
Resistance

[CohenC]

Re: ASUS UX360UA Turns On No Image

Thanks for your response.

I had read about certain rails always shorting to ground, but it's nice to see it in practice

I don't have one, however, this is now a good reason to get one, it's been on my bucket list for a while.

I will attempt to flash the BIOS and get back to you!

[caspian]

Re: ASUS UX360UA Turns On No Image

how much is the resistance to GND on the 0-volt coil?

[piernov]

Re: ASUS UX360UA Turns On No Image

If caps lock key triggers caps lock LED it typically means it's POSTing correctly. Check if it does the same with external keyboard.
Also what about image/backlight on internal display?

[CohenC]

Re: ASUS UX360UA Turns On No Image

how much is the resistance to GND on the 0-volt coil?

9.5-10 Ohms

If caps lock key triggers caps lock LED it typically means it's POSTing correctly. Check if it does the same with external keyboard.
Also what about image/backlight on internal display?

That's what I came to believe as well, but would it be common for a BIOS chip to have 0-volt pins?

Nothing on the internal display and many 0 volt pins on the connectors connecting the screen as well; yeah the LEDs on an external keyboard do respond to lock keys.

I'm assuming the 0V coil is which is closest to the SSD powers that, would I be correct in assuming this likely won't be activated until it is called for by the BIOS?

[caspian]

Re: ASUS UX360UA Turns On No Image

Disconnect the internal display and HDD, then test HDMI.

[stingerchamp]

Re: ASUS UX360UA Turns On No Image

If external keyboard is working then it is indeed not a bios issue but bios chip pin ,1,2,5,6 should have voltage fluctuating or stable as frequency signals
Maybe different bios chip

Do as suggested above

Hmm interesting

[CohenC]

Re: ASUS UX360UA Turns On No Image

Disconnect the internal display and HDD, then test HDMI.

No dice, same result. The display connectors have multiple 0 volt pins as well.

If external keyboard is working then it is indeed not a bios issue but bios chip pin ,1,2,5,6 should have voltage fluctuating or stable as frequency signals
Maybe different bios chip

Do as suggested above

Hmm interesting

Have ordered a programmer, will arrive in a couple weeks I hope.

In the meantime, I monitored pins 5 and 6 during the boot cycle and they DO indeed fluctuate for the first 10 or so seconds before stabilising at 0V afterwards; pins 1 and 2 remain largely stable.

[caspian]

Re: ASUS UX360UA Turns On No Image

Now, more tests have to be done on this laptop to find more clues. such as DVD drive and HDD activity.