Re: [Sheflug] Power Failure - Dead machine. What to check?

[Alex Hudson <nospam [at] alexhudson.com>]

On 31 Jan 2001 14:36:48 +0000, Barrie Bremner wrote:
> The fuse in the kettle lead hasn't blown, and I've got the PSU apart to
> check the fuse (6.3A) in that. However, is there anything obvious I can
> check?


Yes. Scorch marks. If the psu took a bigish voltage hit, I would expect
to see a few capacitors blow their top. You can't miss it. Same for
resistors - they go a charred black colour, and the board will have
brown marks surrounding the device both on top and below.

Other thing to check - scorched tracks. Follow the tracks on the board,
and see if any have cracked / melted / lifted, which is unlikely but
possible. If you have a multimeter, you can check for continuity.
Another thing to check for is the diode rectifier if you have one - it's
square, black, big and has four pins in each corner. It should allow
current from pin to next pin in one direction only, and you should see a
~.7V drop across them, depending on type. If it allows current both
ways, or neither way, you're not producing DC voltage hence no power to
motherboard. Apart from that, there's not much in a power supply,
depending what type it is. If it's switched mode (most likely) there
could be some big trannys on there as well, which would probably shed a
leg or two in 'bad' conditions ;)

Replace the PSU, if you can, and check the mobo. It's possible it's
fried. If you can, check the voltage on the PSU. Plug it into the mains,
and turn it on. If it's an old PSU, it's not gonna start - the fan won't
even turn around. If it starts (i.e., the fan goes round) you can be
fairly sure it's working. If it doesn't start, you need to find a load.
I would suggest a disk drive, or hard drive, or something else. It's not
likely that plugging in something working to a bad PSU will make the
working device break, but it's possible, so be warned. If the PSU
doesn't start even with something plugged in (i.e., a device of some
sort) your PSU is bust.

Warning: OPENING A PSU IS DANGEROUS. YOU **CAN** PUT YOURSELF IN DANGER.

Even a PSU not plugged into the mains is NOT safe. For it to be safe you
need to leave it about 24 hours. At best, all you'd get would be a shock
or a spark, at worst, depends on the PSU.


> Is the PSU going to take the hit if there was any kind of surge, or is
> it going to take the mobo+chips out? Can't see any obvious damage.


Get a multimeter and find out. DON'T TOUCH YOUR CASE while playing with
a PSU. If your earth is playing up, you could get a shock. Remember,
PSUs sink electricity down cases, and if the earth is blocked the
current sinks down you when you touch it. Same goes for the case of the
PSU. 

In terms of chips, the ones most likely to go would be the RAM or the
BIOS  - I would doubt it would be the processor, but anything's possible
I suppose. 

Hope that helps!

Cheers,

Alex.
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