Asus VW221 (model VW221d)

[bocca]

Hi guys

So I have this Asus VW221. Its problem is, the backlight's not working at all. No seconds to black. It's all black right away. There's a picture on the screen, all OK as it should be, just no backlight.

I opened it up, and there are no bulged caps, visually, nothing out of the ordinary. Little did I find about this screen and this problem, but some are talking about trafo(s).

Here are the photos, and I hope someone will be able to help

[budm]

Re: Asus VW221 (model VW221d)

Check the SMD fuses (F801, F902) by the connector CN902. If F801 is blown, then you may have bad Q802, Q803.

[bocca]

Re: Asus VW221 (model VW221d)

they're up and running

[budm]

Re: Asus VW221 (model VW221d)

How? Details?

[bocca]

Re: Asus VW221 (model VW221d)

I meant fuses, sorry. They are not blown

[jetadm123]

Re: Asus VW221 (model VW221d)

Check to see if the 12-14VDC is present at the fuses F801 and F902.

[bocca]

Re: Asus VW221 (model VW221d)

16.13 V on both fuses

[bocca]

Re: Asus VW221 (model VW221d)

And one correction. Picture appears for about half a second. I was mistaken at first

[budm]

Re: Asus VW221 (model VW221d)

Can you provide the P/N as printed on the two inverter transformers so we can look up the pinout to check the HV winding resistance? Also get te P/N of the two SMD MOSFET so we can verify if they are OK or not.
You can have lamps problem also.

[bocca]

Re: Asus VW221 (model VW221d)

Here's trafos.

Now, if I'm not mistaken, I see four mosfets here. One on the top side, a three on the bottom side. Which ones are you interested in?

[budm]

Re: Asus VW221 (model VW221d)

There are only two power SMD MOSFET: Q802, Q803. They are Dual-MOSFET (two MOSFETs in one package).

[bocca]

Re: Asus VW221 (model VW221d)

Dammit, now it's so obvious. Well, excuse my ignorance.

"NIKOS P5506HVG" both of them

[jetadm123]

Re: Asus VW221 (model VW221d)

You can try taking a resistance measurement across the secondary of each inverter transformer. I believe they are pins 8 and 9 stamped on the bottom of the board.

You can check each of the P5506 mosfets for shorts. Each P5506 contains two mosfets. With your meter set to resistance check the combination for each P5506:

G1-->S1
G1-->D1
S1-->D1
G2-->S2
G2-->D2
S2-->D2

[bocca]

Re: Asus VW221 (model VW221d)

With my multimeter (Mastech MS8200G) set to 2k the inverter transformer readings are:

T802 - .813
T801 - .838


As for the mosfet readings, my multimeter is set to continuity test, or 2 ohms. That is the only setting that gives any reading.

Mosfet Q802:

Red probe on S1 Black on G1 - 1.305
Black on S1 Red on G1 - .664

Black on G1 Red on D1 - 1.879 after some time. Looks like mosfet is charging up.
Black on D1 Red on G1 - .961 (meter beeps for continuity for a second and then stops and gives measurement. edit: beep happens only the first time. every other measurement gives no continuity)

Black on S1 Red on D1 - Meter beeps for continuity for a brief moment and then it goest to infinite resistance
Black on D1 Red on S1 - Meter beeps for continuity for about a second and then measures .315



Red probe on S2 Black on G2 - 1.305
Black on S2 Red on G2 - .663

Black on G2 Red on D2 - 1.885 after some time. Looks like mosfet is charging up.
Black on D2 Red on G2 - .959 (meter beeps for continuity for a second and then stops and gives measurement. edit: beep happens only the first time. every other measurement gives no continuity)

Black on S2 Red on D2 - Meter beeps for continuity (only the first time) for a brief moment and then it goest to infinite resistance
Black on D2 Red on S2 - Meter beeps for continuity (only the first time) for about a second and then measures .314

[bocca]

Re: Asus VW221 (model VW221d)

Mosfet Q803:

Red probe on S1 Black on G1 - 1.303
Black on S1 Red on G1 - .663

Black on G1 Red on D1 - 1.880 after some time. Looks like mosfet is charging up.
Black on D1 Red on G1 - .958 (meter beeps for continuity for a second and then stops and gives measurement. edit: beep happens only the first time. every other measurement gives no continuity)

Black on S1 Red on D1 - Meter beeps for continuity for a brief moment and then it goest to infinite resistance
Black on D1 Red on S1 - Meter beeps for continuity for about a second and then measures .313



Red probe on S2 Black on G2 - 1.303
Black on S2 Red on G2 - .662

Black on G2 Red on D2 - 1.885 after some time. Looks like mosfet is charging up.
Black on D2 Red on G2 - meter beeps for continuity and then shows infinite resistance

Black on S2 Red on D2 - Meter beeps for continuity (only the first time) for a brief moment and then it goest to infinite resistance
Black on D2 Red on S2 - Meter beeps for continuity (only the first time) for about a second and then measures .313

[jetadm123]

Re: Asus VW221 (model VW221d)

I believe the continuity setting on your meter is the same as the diode check setting and what you're reading is voltage and not resistance. From what you said, you tried measuring resistance on all resistance settings and saw nothing? The meter does read zero ohms when you touch the pos and neg probes together, correct? Is it's battery good?

[bocca]

Re: Asus VW221 (model VW221d)

Battery is new.

Yes, resistance is zero on all other settings

[jetadm123]

Re: Asus VW221 (model VW221d)

I don't think I've ever heard of all 4 mosfets on Q802 and Q803 shorted out, but if you're reading zero ohms for each measurement, then they'll need to be replaced.

[bocca]

Re: Asus VW221 (model VW221d)

well whadiya know. I replaced the battery and the results were the same.

So i got another multimeter (another mastech) and the results are now different


multimeter's set to 2k.

q802

G1-->S1 - 1.609
G1-->D1 - 1.094
S1-->D1 - 0.267
G2-->S2 - 1.612
G2-->D2 - 1.093
S2-->D2 - 0.267

q803

G1-->S1 - 1.609
G1-->D1 - 1.093
S1-->D1 - 0.267
G2-->S2 - 1.612
G2-->D2 - 1.093
S2-->D2 - 0.267

[jetadm123]

Re: Asus VW221 (model VW221d)

Check T801 and T802 again. If those readings are consistent I would check the CCFL bulbs using budm's method in post #2.