Asus VH238 Shortcircuit

[lion_sta]

Hello,

I had this monitor for 3-4 years or so. About half a year back (when I knew less about monitors than I know now) it started shutting of after a couple of hours and I would have to let it through the night to be able to start it again.

Recently tried turning it on after quite some time and it wouldn't.

So I disassembled it and turned it on to see if something is wrong. Long story short, a metallic foil got on the power board and made a short - there was a spark. It wouldn't start at all.

Ok, damage check - removed quite a few components and most seemed to be fine. There was a resistance that didn't show any value - open probably.

Would try to replace it but it has some weird lines and cant understand what is its resistance - It's the small one in the image with two resistances: Violet, Green, Silver, Gold, Green.
The silver line has me baffled.

For now I would appreciate some help with identifying the resistance.

Thank you

P.S. I have repaired one monitor already thanks to you

[1supertech]

Re: Asus VH238 Shortcircuit

According to my trusty cell phone resistance calculator The silver line has to be gray resistance is 75.8 +/- 5%

[stj]

Re: Asus VH238 Shortcircuit

some bad solder joints there
and one foto looks like the audio amplifier may be burned

[lion_sta]

Re: Asus VH238 Shortcircuit

I see. Will look for that resistance.

The audio part - not such a big deal.

Any of you have the service manual or the schematics of the board? I will want to know what voltages I need to have at the exits, where is the ground.

[lion_sta]

Re: Asus VH238 Shortcircuit

Also, if I can't find this very resistance, what is the closest resistance that I can get away with?
50 Ohm I think would be too little?
100 Ohm, will it start at all?

[stj]

Re: Asus VH238 Shortcircuit

I see. Will look for that resistance.

The audio part - not such a big deal.

it is a big deal, if it's burned it could be shorting out the supply section!

[lion_sta]

Re: Asus VH238 Shortcircuit

Right. If I remove it completely, would that do?

but first I'll check if it's actually faulty. Thanks.

[stj]

Re: Asus VH238 Shortcircuit

if it's shorted out, you must remove it, but the monitor will run fine without it - so no need for a new one.

[lion_sta]

Re: Asus VH238 Shortcircuit

How about that resistance, do you think I will mess it all up if I replace it with something not quite the same?

[budm]

Re: Asus VH238 Shortcircuit

That is 0.15 Ohms resistor for the Source pin of the power MOSFET (which drive the main power transformer), if that resistor shows open circuit then the MOSFET is shorted out which in this case the SMPS IC should also be replaced at the same time.

[lion_sta]

Re: Asus VH238 Shortcircuit

Wish I knew how you figured that out.

Thank you either way.

Do you mean I need to also replace the one I marked with one?

[budm]

Re: Asus VH238 Shortcircuit

Does that '1' MOSFET has low resistance reading between Source pin and Drain pin, Gate pin and Drain pin?
BTW, before you removed bunch of parts from the board, did you check and see if you have any DCV at the white connector that goes to the main/Logic board?
So that 0.15 resistor shows <1 Ohms on your meter?
Also when you said the monitor starts shutting down, do you still see power LED is still on?

[lion_sta]

Re: Asus VH238 Shortcircuit

That resistance, that is also circled in the image, shows open circuit. No reading whatsoever.
Without removing the MOSFET from the circuit I get very low resistance between the S and D, G and D, and S and G.
I did check but wasn't sure what values I was supposed to have or which one was the ground pin. This is why I haven't put down the results. So not sure.

[budm]

Re: Asus VH238 Shortcircuit

That resistance, that is also circled in the image, shows open circuit. No reading whatsoever.
Without removing the MOSFET from the circuit I get very low resistance between the S and D, G and D, and S and G.
I did check but wasn't sure what values I was supposed to have or which one was the ground pin. This is why I haven't put down the results. So not sure.

You need to remove that MOSFET and test it again off the board at this point.

[lion_sta]

Re: Asus VH238 Shortcircuit

Did that with the MOSFET out of circuit and the same thing. Very low resistance among all pins. Guess it's bad.

[budm]

Re: Asus VH238 Shortcircuit

Did that with the MOSFET out of circuit and the same thing. Very low resistance among all pins. Guess it's bad.

And that 8-pin SMD IC close by that MOSFET should also be replaced too.
You also need to check the resistors/Diode that are connected between the Gate pin and the IC to see if they are also damaged or not too.

[lion_sta]

Re: Asus VH238 Shortcircuit

Can that SMD IC be checked?

I am going to hate these resistances by the time I'm done with repairing. The other two are not too clear either. One of them shows no result. The other one shows something in the Mega Ohms.

[budm]

Re: Asus VH238 Shortcircuit

Can that SMD IC be checked?

I am going to hate these resistances by the time I'm done with repairing. The other two are not too clear either. One of them shows no result. The other one shows something in the Mega Ohms.

No way to be 100% sure if the IC is bad, you can do resistance testing between pins but you will have to get the spec sheet of the IC first to get the pinouts of the IC.
If you do not change the IC, there is real chance of blowing up the new MOSFET and the resistor.

[lion_sta]

Re: Asus VH238 Shortcircuit

I can't seem to find anywhere that IC.

Worst case scenario I will order the whole power board from Aliexpress.

But I will try to start it with the new mosfet and resistances.

[lion_sta]

Re: Asus VH238 Shortcircuit

Ok, I need your help guys.

I have the A 2761I MOSFET and the SMD IC - SPW-205 (SBI4 . 2 E156193 FEC 1110 A)

I cant find them both here, where I'm from. On Aliexpress I can find only the MOSFET.

Is there some alternative to these components?