Asus Power supply Help

[Crazycuda]

Hi all,
First time post could really use some help on this one. Brief story its an asus 27" monitor that the cat knocked over and it never powered on again, not even the power light comes on. Anyhow I pulled it apart and saw 2 caps were kinda bulged on the top. (Marked with red dots in pict) so I replaced them. I also checked all the fuses on the board they passed. Tested it and still no power, I checked the main cap and when the board is plugged in its showing approx 170vdc. If I pin test the connector (all the +5v wired that goes to the logic board) are only at 1.7v.
One thing I did note and hopefully it can be seen in the Pict is the back of the power supply board did make contact with the back of the lcd display and left a few burn marks on the metal display backer.
Anyone have any suggestions on where I should go next or where I can test to verify where the issue is. I have hunted and no luck on finding a flow chart for this board. I have even hunted for a replacement board and it seems to be that one odd ball no one has.

[CapLeaker]

Re: Asus Power supply Help

We are going to need a high resolution, straight shot picture of the back of the PSU. We need to be able to see details on it.
Unplug the main board from the PSU, plug the PSU into mains, then measure the DC voltage on each pin (pic 5). Post the pin out names with the voltages measured.

[budm]

Re: Asus Power supply Help

Those two red box fuses are good?

[Crazycuda]

Re: Asus Power supply Help

Best pict i could do with the lighting in the room... Will post power numbers shortly..
all 3 red box fuses check good

[Crazycuda]

Re: Asus Power supply Help

Using pict 5 as reference
pin 1 ground
pin 2 na
pin 3 2.2vdc
pin 4 2.2vdc
pin 5 0 (dimm)
pin 6 0 (on/off)
pin 7 na
pin 8 na
pin 9 na
pin 10 2.2vdc
pin 11 2.2vdc
pin 12 ground
pin 13 ground

[CapLeaker]

Re: Asus Power supply Help

That's with everything disconnected from the PSU? Check D908 or D906?

[Crazycuda]

Re: Asus Power supply Help

Yes,
Testing the board on the workbench.
No I haven't checked those yet. That was going to be tonight's project

[Crazycuda]

Re: Asus Power supply Help

DE-soldered and tested both parts. According to my Mega328 tester they are good. What has me scratching my head is the 4 wire connector/harness (3 yellows and one black) are reading over 5v (yellow wires) I'm partly wondering if one of the coils could be bad. If i probe on L905 i get 1.9v on one leg and 0 on the other. I tried hunting that parts PN. to see if I could find any specs and no avail on google.

[CapLeaker]

Re: Asus Power supply Help

Take it out and check the inductor. Maybe it is open. Could be, wouldn't be the fist time that a inductor broke a leg etc. Look further upstream. Usually there is diode, a capacitor an inductor, another capacitor etc. Take that inductor out and check the cap after the diode.

[Crazycuda]

Re: Asus Power supply Help

De soldered the inductors , and every diode checked each one. All checked ok, Found another psu on ebay going to pick it up. (supposedly new) Once it gets here (and test it) I am going to use that as my reference to figure out what went bad on this board for my own sanity lol. Ill post what I found to be the culprit.

[budm]

Re: Asus Power supply Help

It looks like all 3 power supply outputs are all low, it can be bad feedback due to bad ref diode such as TL431, opto, etc.
You have 3 rectifier diodes that for sure all tested good?
The output Voltages (+5V, +5V1, +18V) on all 3 test points I marked are stable?

[Crazycuda]

Re: Asus Power supply Help

Attached volt notes to pict.