Hello Folks !
Here's my latest cause of neuro-hypertension !

I approach my CPU (an old P3 having an Intel 810 chipset with CD R/W, 512 MB Ram, 160 GB HDD, Floppy, USB controller) with noble intensions.

As I turn push the power-supply on-off switch, I hear a wierd, cracking sound and the next instant I realize that my lights are out ! The mains of my electricity fuse box trip ! I pull the circuit breaker back up and try to repeat the now nerve-wreking task of turning on my CPU. It's dead ! It won't respond to the switch: no leds, no fans, no motors run ! My monitor which recieves its supply from the CPU (via the mains cable) turns on !

Next, I open the CPU with an attempt to find smoke, melting plastic. Fortunately (or unfortunately), there's no trace/smell of smoke. Now I try and hunt for the fuse, but alas, the damn PCB is so cluttered, that I can't find it.

So now I'm trying to trouble shoot whether it's a repairable problem (a simple task of changing the fuse somewhere) or whether my PSU has gone dead !

Needless to say, this is the first time, I've encountered such a problem and have no clue how to proceed. I shall lay my hands to a DVM to rule out the PSU...but first I need to buy a DVM ! (i've moved out)

Can someone throw some time to solve this mystery ?

 

Presumably the PSU has died?, as it tripped your mains then obviously something has gone S/C. Best idea is to just buy a new PSU, they are freely available at reasonable cost.

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The power for the monitor is in parallel to the input, so it makes no difference if the rest of the supply is cactus. Which is why your monitor is still turning on.

Computer PSUs don't generally have a fuse, so there is minimal point looking for it.
The switch is wired to the motherboard, the motherboard tells the PSU to turn on, so you could have fried your MB too... the way to check to see if the psu is still working is to short the green wire coming from the PSU to one of the black ones (doable by removing the connector from the MB and using a paperclip). Ensure you exersice caution in doing this.
If the PSU turns on, then you know it is still working. If you hear EHT rush (or absolutely nothing) then you know it's cactus. You can now rule out the PSU or MB. Then you get to work on the other one.

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What is a joule per second?

 

Is it the fuse breaker thats gone or is it an earth leakage circuit breaker ?

If its the earth breaker then it could be the input filter breaking down.

 

This is an AT system, so is there a connection to the motherboard ??

Besides I've disconned by PSU out of the system, its only got the regular bunch of voltage and gnd wires (yellow, red, black, orange, blue, white) and 4 wires that clip into the DPDT switch. Another question...the wires to the DPDT s/w are blue, white, brown, black. In my ravenous desire to check my PSU, I did not pay attention to the orientation, can you tell me what goes where on the s/w ?

 

Ahh that could well be your problem then - there is a neutral and live feed to two terminals of the switch which then goes to the neutral and live input to the power supply (the other two terminals). Sounds like you have the DPDT switch wired up to short out the live and neutral feed.

 

ahh you see, this is where the diode tester comes in handy on the DVM... lol..
get your hands on a multimeter, even if it doesn't have a diode tester just use the resistance tester, and check to see which terminals are shorted togethor when the switch is pressed.

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What is a joule per second?

 

Yup, that was it ! I had checked it on a DVM, it was dead ! Perhaps one of the components gave way, system went s/c. Lasted me for 7 years though !
Got a new one, up and running