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repairing a psu

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#1
Will

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Hi all,
I need to replace a psu fan (custom compaq deskpro EN psu).
I know the capacitors are slightly dangerous, do they discharge over time. or is there a 'correct' way to safely discharge them.

Don't wanna get fried AGAIN!

Will

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#2
fraser

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It's 12V, provided that your hands are dry you shouldn't be getting any shocks. Wait an hour or two to be safer, and if you are really paranoid, use a 1 Meg Ohm resistor to discharge.

In a PC power supply, the capacitor is on the secondary stage, and it should be low voltage.

Leave it connected to a PC overnight, with no mains supply connected if you want complete discharge.

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#3
Will

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ok i'll try later on..

also a fan on a psu, (this is wierd! it's on the 'inner' side of the case.
should i suck or blow (i guess blow, as then it will blow air over the cpu heatsink?)

Will
(buy case and chip for a fiver, spend 20 hours repairing.. what a deal!)

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#4
fraser

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Today is your lucky day! I have a Compaq EN myself, the slimline one.

There are two fans in the PSU, yes? I think they provide a flow through the PSU, the internal one draws air from inside the computer, which goes through the supply and out the back fan.

I'll check tonight when I get home for sure, but I think that's how it goes. Need to be careful inside my EN though, I've 'modified' it to take two hard-drives by removing the floppy and doing some rewiring...but the wiring was done before I realised you could get PSU Y-splitter cables, so I'm using terminal blocks to get the power to the drive. :)

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#5
Syvwlch

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Well...

Now we know how much you think your time is worth! Have you shared with your employer?

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#6
fraser

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It's a slimline PC, Compaq would probably charge an arm and a leg for a replacement PSU. It's a wierd shape.

The EN is a funny machine. It's designed for businesses, so everything is hinged for easy access. You can take one apart in seconds, but spares probably aren't easy to come across.

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#7
HelloDave

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Be careful with computer PSU's - switching power supplies carry a lot of current in their capacitors even after they're switched off, as anyone who's got a shock from the SPV charger will testify! If you touch the wrong part at the wrong time it could be serious! Just because the PSU outputs 12v doesn't matter, it still takes mains voltages in, and also outputs quite a bit of current - they have special security screws in for a reason! Replacing a fan should be OK, but being cautious is the best approach; other people have modded PSUs so a Google search could be useful. BTW, normally fans have a helpful arrow printed on them to indicate the direction of airflow - have a look for one before you take the fan out and can't remember which way round it was!

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