Help with adaptor 2001fp from dell

[charliemany]

Hello,

This is my first post. I am a student, who is just starting to become a mechanical engineer.

I have an old dell monitor that doesn't work. As the headline states it is a 2001fp and the adaptor goes AC to 20v 4.5A DC.

What I have done so far...

Plugged into a working outlet. OK
Tested the 2 piece cable from wall to adaptor. OK
Tested Adaptor to monitor. NOT OK
Opened adaptor, properly discharged the Capacitors and took a look, seems fine.
Desoldered the DC cable from the PCB and tested continuity. OK

Plugged in the adaptor. LED came on. Voltage at DC output starts at 20V and fades to Ziltch. Everytime I unplug it and wait a bit then plug in, the LED comes on and then the DC voltage slowly fades out. The large Cap is also discharging without help.

Anyone have a clue how to help or whats going on? I'm new to electronics and thought this would be a nice beginners experience.

I'm guessing that there is a short back to ground or something?

Going to bed now, so no rush.


Two holes (first pic) on left bottom and (second pic) left top, are DC 20V output where the cable was removed. Just to get an idea what I'm looking at.

 

[Harald Kapp]

Your images are of low quality, hard to judge anything by them.
The standard culprit would be one (or more) electrolytic capacitor, presumably the big one lying sideways. Check all electrolytics for signs of swelling or leakage.

I'm guessing that there is a short back to ground or something?

A short wouldn't allow buildup of the output voltage in the first place and would also drain any capacitors rather quickly, not slowly.

I'm new to electronics and thought this would be a nice beginners experience.

Actually a switch mode power supply is not a good starting point for beginners as it deals with high voltages and/or currents and is also technically not a simple circuit.

 

[charliemany]

I have decided to just disassemble the unit for components and use them to build simpler circuits. I don't have a very good soldering iron and I accidentally made a mess of the resistors in my attempt to remove the large capacitor. I dare not run power through the brick now.
There was no swelling or leakage that I could see on any of the capacitors that I could see.
I am on he look out for a working power brick and will just solder on the Dell proprietary cable since it has continuity at all pins.
Thanks for the reply Harald