OK, this may seem like a waste of time considering desktops are practically obsolete and power supplies are widely available. Why would anybody want to fix this component?
Well, as it turns out I truly need to fix this power supply and I am thinking some member may have actually gone to the trouble of fixing (or at least trying to fix) this kind of power supply. Unless of course, the typical failure mechanism is some kind of proprietary chip in which case all hope is lost…
I already purchased a spare, but I could truly use one TODAY! (ahh, Murphys law…)
What I see is that the amber light inside of the mother board lights up, but the computer does not respond to power on commands. I have seen this before on previous defective units. Oh yes! I have a pile of defective units which is why I am wanting to try and fix them up instead of buying more!
Needless to say, I know the problem is the PS and not the mother board or any other component. It is the darned PS, which is made like a frigging fuse! On its behalf, the unit was subjected to a bunch of GFCI kicks a few days ago, so it doesn’t surprise me if this is what cook it.
What does usually goes with these guys? Are they simple to repair? Thanks for any input on this matter!
Here is a post I found on that (and a common issue with computer power supplies in general)
“Just an FYI, I was able to revive a fairly new Dell power supply XW784
aka DPS-250AB-28 that was out of a Dell Inspiron 531S that wouldn’t turn
on. There was a lone 16v 1500uf cap that had bulged. I didn’t
desolder it but just pulled it out with pliers, I noticed that one of
the leads just pulled right out of the solder joint as if it wasn’t
attached. I soldered a new Rubycon in and it started right up!”
In general with unknown electronics, try to use your senses. Visually inspect and sniff - do you smell a burned component? Do you see a charred power resistor or a burned up trace? Is there an obvious cold solder joint or a component that was never soldered properly? Besides the bulging caps, another visual is a regulator or IC that has overheated and leaves a characteristic hole or radial cracks in the ceramic / plastic encapsulation. (attached visual)
It may be as simple as one component, or you could have a cascade failure. I have seen shorted caps / diodes take out a power resistor, trace and a regulator if you are particularly unfortunate. But having no cues at all makes it rather difficult to troubleshoot without a schematic that documents typical voltage readings. (but you do have the other supplies to compare against)
Since this works on 120 VAC, I have to caution about diagnosing this as the main power caps may still be charged and can deliver a jolt even when unplugged. If you decide to take measurements while it is energized, (and I can’t officially advise that you do this) you have to trace your power through the transformer, bridge rectifier, regulators, etc. and it helps to have good sharp probe tips that won’t slip and short something else out.
In support of JAGMAN’s post, one of the most common components to fail on any piece of electronics is a capacitor. It’s usually a good place to look first. That’s especially true of power supplies.
Beware of working on power supplies; they will maintain a lethal charge on the good capacitors for up to a few days after they have been powered. Always short your power capacitors before working on them. You should also follow the “one-hand” rule, that is, only use one hand inside high voltage electronics. The theory is that if you do short out a high-voltage component, the current would go down your side, instead of through your heart. It only takes a milliamp to stop a human heart.
Most techs or shops in the US don’t repair power supplies, largely because power supplies are so cheap and easy to get. I was surprised to see repair instructions on a newsletter that I get from India. Apparently, they find it worth their while to do those repairs.
The Electronics Lab now has an ESR meter that you can use to test for bad caps in power supplies for PCs, monitors, TVs, etc… It will show you that caps that physically look good, have good capacitance readings, but yet will cause failures in circuits because of being way out of line on ESR.
Also, if you want to learn more about repairing switching power supplies, check out this entry in my repair logs out on the NLG forums: