it's possible to trace the location with a current source (bench top power supply) and a sensitive volt meter by measuring the voltage drop along the current path.
I think you mean current injection, I learned about this technique and I'm interested to use it.
I have a bench power supply, I might try to apply this method but the problem is that where I start to inject the current ? Because I don't have the schematic, so I might continue to just take off the components until I find the faulty one.
I imagine I'd lack hope of reassembling the entire unit.
I recorded them with the component value and its number on the PCB, nice thing that Dell put the parts' names on the PCB, otherwise things could be more difficult and I may not be interested to work on such unit.
suggesting failure of a component at the heart of operation
I checked the SMPS switcher but it didn't measure short. I'm thinking of the PFC.
I'm going to take off the components one by one until I find the faulty one.
Can you locate the 5v & 3.3v smoothing caps, remove and test them?
That's what I did in the picture in #2. If you check the picture in #1, the caps on the left are the output caps, in the 2nd picture I took them all off.
I tested them and they all charge up with the ohmmeter. But there's one that's a little bit bulged but when I tested it, it still works.
I think you may be repeating a mistake made by many people. The rectifiers (marked with 'D') on the PCB will have a low resistance transformer winding across them so it is quite normal to measure them as short circuit while in the PCB. The only way to test them is out of circuit.
Yep, that's what happened and I took them off, tested them and they are working.
It is also normal to measure a low resistance, although not zero Ohms, across the 3.3V and 5V outputs
That's still a not clear area for me, I just now checked my Corsair PSU that's on the shelf for months and the output rails measure very high resistance from hundreds kilo ohms to mega ohms.
And when I short them out, and start to measure them again, the resistance is increasing, meaning the output caps are charging.
Now I'm starting to connect some thoughts; the last thing I tested on the faulty PSU when I took all the output caps off, the 12V short went away and measures like 143 ohms, but the 3.3V and 5V are shorted out.
So if the output power MOSFETs are off the PCB, then I'm thinking of the HFT that is not likely to be broken but I might take it off eventually to trace the source of the shorts, but I also might take all the components before taking the main HFT.
If removing the capacitors on the 12V output took the short away, that may be the only faulty part.
Only the short on the 12V rail went away but still on the 3.3V and 5V rails.
I'm planning to take everything off until the short on the output rails is fixed, the PSU is considered out of service and going to be thrown anyway, and I like to fix them with the good protection of using the lamp limiter so I feel safe not to have explosions from failed repair attempts.
Note that it may not work if you simply leave the capacitors out of circuit because the ripple on the feedback path may be too much and cause a shutdown.
I won't do that, when I find the faulty component, I will order a replacement, and then put everything back to its place and run the PSU.
Of course I'm using the lamp limiter, in case, if I didn't do the repair process correctly.