Help needed to revive dead Asus EXA082XA AC adapter

[mikey5791]

Hi all,
This model EXA082XA Asus ac adapter just died.
Opening the case, there is no burn mark or any damage component. Glass fuse still has continuity. Diodes and 2 transistor has not shorted. I just suspect a 8 pin ic label Chip Rail CR-LSN69 but unable to get any datasheet.
Does anyone know how to test this ic or any equivalent substitute such as TOP258PN can be used?

Any kind assistance and guidance is highly appreciated. Thank you.

[stj]

Re: Help needed to revive dead Asus AC adapter

check the output cable for breaks or shorts.
people like to abuse psu's by wrapping the wire around them all the time.

[mikey5791]

Re: Help needed to revive dead Asus AC adapter

Hi stj,
Checked the output cable. It has continuity from multimeter probing. No breaks or shorts.
I did a dc voltage checking with live ac power on.
The big brown main cap and the nearest 3 pin transistor has about 250v dc. But there is no voltage on capacitor C5(22uf50v). This should be the startup cap. So i suspect the 8 pin ic on the primary side is bad. Fyi, i don't detect any other voltage beyond the C5 cap.

[lotas]

Re: Help needed to revive dead Asus AC adapter

You should have a big capacitor around DC 300v, check that capacitor.

[mikey5791]

Re: Help needed to revive dead Asus AC adapter

Hi lotas,
Sorry my mistake was that earlier on i took dc reading from an analog multimeter. Using a digital multimeter, i got 324vdc from the main big cap.

[stj]

Re: Help needed to revive dead Asus AC adapter

yea, rectified mains is x1.41
check for bad resistors that feed the mains dc to the startup cap

[stj]

Re: Help needed to revive dead Asus EXA082XA AC adapter

based on this:
http://www.chiprail.com/pd.jsp?id=86#_pp=2_321

[mikey5791]

Re: Help needed to revive dead Asus EXA082XA AC adapter

Hi stj,
Sorry for late reply as i had been occupied with some other matter.
Found one resistor R76(brown,black,green,gold) which should be 1M ohm but no reading on DMM after i desolder one leg.
I will look for replacement and see if it fix the no power issue.

[mikey5791]

Re: Help needed to revive dead Asus EXA082XA AC adapter

Hi stj,
Finally i got time to buy the 1M ohm resistor and replaced the bad one at R76.
Now the AC adapter output led lights up and it is working. Great thanks to stj for the help.