Dell PC Hardware Problem

I have a Dell XPS410 desktop PC. It’s about 5 years old, I’d guess, and FWIW, runs Win 7 only - no dual boots or anything.

I don’t think that’s relevant, though, because the machine will not even come close to booting. It conked out while I was using it about 8 hours ago, and when powered on all I get is an amber power light (it’s usually green) for a few seconds. I hear the PSU fan spin up for maybe two seconds, then it all powers down. If I leave it connected to mains power, this simply repeats ad infinitum. Nothing on the screen, no Dell diagnostic lights.

I have tried disconnecting the 24 pin motherboard connector and jumping the green and black leads - PSU fan spins up like it was going out of fashion, so PSU probably OK? I have removed all PCI cards (graphics and a sound card), disconnected all drives (2 HD and 2 DVD, all SATA), and removed the 4 1Gb memory modules. I have also disconnected the internally connected USB multi card reader.

All to no avail. Is there anything else I could try? Or should I treat this as a dead motherboard? If anyone has any thoughts, I’d be very grateful.

Most likely bad PSU. Happens all the time.

Think so? That would be good, because I could easily replace a PSU (have done so in the past) but wouldn’t relish attempting a motherboard.

Plus, I could probably find a spare PSU without too much trouble and for no money, though not a Dell one.

PSU’s often just fail on one line, you may have good 5v but not 12v or vice-versa.

That seems unlikely, since all of the voltages come from one transformer, as shown here, and failures in a switchmode power supply usually involve complete failure (I have never seen such a failure that didn’t knock out the whole thing). Note however that newer PSUs have a standby power supply (not shown with the example I gave, which was an older design, but they are still basically the same) which supplies power all the time; a failure of the main power section, if the fuse doesn’t blow, won’t knock the 5 volt standby output out, which might cause the odd symptoms reported by the OP. A more likely cause is defective capacitors in the power supply, which will cause it to shut off due to excessive ripple and inability to regulate (a good power supply should shut off and stay off though, not cycle on and off)

Thanks guys. I’ll look for a spare PSU somewhere and test.

I don’t really have a way to test the different rails that I know of - PSU won’t stay alive for long enough to use my multimeter, so I have no idea if the 12v is OK while the 5v has failed, or whatever.

Please keep us posted Paul, We Dell owners have inquiring minds!