ASUS VK191S - no power

[ragis]

Hello again, folks !
This time i have a monitor which don't power on or stand by.
PSU - tip019at-01

Checked:

STK0765 - not sure how to test mosfets (put com to source and then charge gate then red probe to drain - gives 1.500 for a sec.) so i'm not sure if it's OK
SBT150-06 - Readings 135 ohms on the two anodes (i think it's ok)

LD7575PS - VCC is 11.25V no shorted legs

Both fuses are OK

The output is 5.0V

There is voltage to the main board and to the button board but there is no power on or stand by

Checked the button board led - OK
I don't have schematic for the psu...

Thanks, again for your kind help and support !

Best regards, ragis

[stj]

Re: ASUS VK191S - no power

nice low-res foto's

list the pins on the psu and what comes out of them.

[ragis]

Re: ASUS VK191S - no power

Sorry for the photos, here's new ones

On pin 3,4 - 5.10V
pin 1,2,5,6,7 - 0V

[stj]

Re: ASUS VK191S - no power

there are a lot of cracked solder joints on that - and i'm not refering to the flux covered resoldered pins.

[ragis]

Re: ASUS VK191S - no power

The solder joints are ok, it seems like that from the flux i used around the pins
But i can resolder them if you think there is a problem, could you be so kind to show me the cracked ones ?

[budm]

Re: ASUS VK191S - no power

The power supply is an always on power supply, since you are getting the 5V for the logic board and the 12V for the inverter circuit, the power supply is find but it is not receiving the command signals from the main/logic board to turn on the backlights inverter circuit or the dimming command signal. The problem is not the power supply board.

[ragis]

Re: ASUS VK191S - no power

The client told me that there was a surge shock and the monitor stopped working i can't locate any burned component .. Can be the logic board get demaged.And last thing how can i test the inverter ?

[stj]

Re: ASUS VK191S - no power

i still see bad solder joints - NOT THE ONES YOU DID.

[budm]

Re: ASUS VK191S - no power

You can test the power supply/inverter board by itself.
I can see three small control line traces, two I can see, the third one I cannot see.
I suspect them to be BL-ON, PWM-DIM, ANALOG DIM.
You can disconnect the logic board from the power supply board, then solder 1K resistor between # 1 and the 5V pin, then a second 1K resistor between #2 and the 5V pin to see if the backlights will come on the second you plug the monitor into the AC outlet, if not add another resistor between # 3 (which I cannot see due to cruds on the pins) and the 5V.
The surge may have come through the Video connections.

[ragis]

Re: ASUS VK191S - no power

Ok, so i added 3 1K resistors to the 3 pins and then without logic board i plugged the monitor in AC and the backlight started blinking.I think that means the inverter is OK.But why it can't power on the monitor and even go to stand by mode... What can i do now ? Thanks again for the help to check the inverter

[ragis]

Re: ASUS VK191S - no power

Just one simple question:
on the logic(main) board there are 2 voltage regulators U1 and U2
U1: pin3(input) - 4.74V pin2(output) - 3.28V pin1(adjustment) - 0V
U2: pin3(input) - 3.28V pin2(output) - 1.78V pin1(adjustment) - 0V
They are both 1117 but i don't know if they are fixed or adjustment the marks are:
U1: 17-33
U2: 17-18

Thanks again

[budm]

Re: ASUS VK191S - no power

U1 is 3.3V fixed
U 2 is 1.8V fixed
So they are OK.

[ragis]

Re: ASUS VK191S - no power

Ok, any other sugestions ?

[ragis]

Re: ASUS VK191S - no power

OK, monitor repaired !!!

The problem was in the logic board SPI flash IC - SST25VF010A
I used a flash bin from VK191D and it worked
Thanks again for the replies and help from stj and budm
As stj recommended i resoldered the whole PSU.

So the solution is to reflash the IC !
Thanks again and best regards, ragis !