Asus VS278 not powering on

[No1baggiesfan]

Hi all,

My daughters BF gave me this monitor to "look at"
It showed a blue LED the first time it was powered, but would not turn on, saw a couple of threads on Asus monitors here, left it a few days, not even a blue LED now.

Story so far......
Fuse tests ok for continuity 0.03 ohm
Big cap 100uf 450v. Old one showed 8.8vdc on live test, replaced it and it now shows 22vdc and dropping, I presume it should be at least 240v ?
Replaced most of the electrolytics, just have 2 left to change.

Havent done V tests on ribbon as the monitor still does not show life and the cap V is too low.

not 100% sure where to look next, was considering changing the 2 small blue caps too.

any help would be appreciated.


PS. the chalk/white lines were already there.

[No1baggiesfan]

Re: Asus V278 not powering on

It is a VS278 lol, cannot edit title

[CapLeaker]

Re: Asus V278 not powering on

Low DC voltage on the 450V main filter capacitor, should be easy fix.just go from that cap backwards.
In standby you should have 325V DC. With the PFC on, you should have something like 400V DC at that main filter cap. That leaves the bridge rectifier, the filter inductor, the fuse and the plug / cable. See if you loose the AC somewhere.

[No1baggiesfan]

Re: Asus V278 not powering on

Thank you for the reply.

240vac at all points before the rectifier, both sides of cap test 240v too, but only 20v across it.

[No1baggiesfan]

Re: Asus VS278 not powering on

Brain fart moment when tested previously, I hadn't bridged the 240v switch DOH!

Ok, 327v across the cap, so I tested v's on the multi lead:

green 0v
yellow 0v
orange 0v looks like ground anyway
blue 5v
grey 5v
purple 5v
brown 0.02v
black 0v

Cannot find a schematic for this board/monitor so I cannot say what voltages should be present at that connector.

[No1baggiesfan]

Re: Asus VS278 not powering on

Bump

[CapLeaker]

Re: Asus VS278 not powering on

Brain fart moment when tested previously, I hadn't bridged the 240v switch DOH!

Ok, 327v across the cap, so I tested v's on the multi lead:

green 0v
yellow 0v
orange 0v looks like ground anyway
blue 5v
grey 5v
purple 5v
brown 0.02v
black 0v

Cannot find a schematic for this board/monitor so I cannot say what voltages should be present at that connector.

Look at the PSU on both sides to see if you find a legend what each bin is. Green 0V doesn't mean anything to anyone. However PSon 0v for example tells the story very quickly.

[No1baggiesfan]

Re: Asus VS278 not powering on

Look at the PSU on both sides to see if you find a legend what each bin is. Green 0V doesn't mean anything to anyone. However PSon 0v for example tells the story very quickly.

There is no legend anywhere, the only markings are on the HDMI board,
black - TP75
Brown - TP76
Purple -TP77
Grey -
Blue - TP72
orange -
yellow - TP78
green - J8 J5

[Lisa Su]

Re: Asus VS278 not powering on

I'm not sure if this is useful since it doesn't contain schematic

[No1baggiesfan]

Re: Asus VS278 not powering on

I'm not sure if this is useful since it doesn't contain schematic

Thank you for posting, I had a similar manual already, but without any pictures lol, the schematic would make things a lot easier tho, there isnt much on the web regarding this monitor.

[No1baggiesfan]

Re: Asus VS278 not powering on

Bump