Taking apart PC power supply precautions?

[smoguzbenjamin]

Hey everyone,

I am about to take apart a PC PSU I have to salvage the 12v transformer and the regulator etc, plus the wires. Are there any precautions I have to take before desoldering everything or is the thing relatively safe?

Cheers,
Ben

[Paul Perry (Frostwave)]

If it is a switch-mode power supply, then one capacitor might be charged to a couple of hundred volts when it is working. Personally, if it hasn't been working for a few weeks, I would assume it to be discharged, but if you wanted to be 100% sure, you could short out any high voltage caps.
(no point shorting out LOW voltage caps, naturally).

[smoguzbenjamin]

I last used it about 4 days ago... But holy crap there's 2 HUGE black caps in there.... And it's riveted together so I'm slowly hacking away  at the enclosure... But I'll short those caps out with a resistor... 470K good enough? 1M?

[Paul Marossy]

They have probably drained by now, but try draining them with a 470K resistor just to be sure.

I have gotten A LOT of wire and caps and stuff from two dead computer power supplies that were thrown away where I work... and they threw out an old fax machine once, which was a gold mine for salvaged parts!

[smoguzbenjamin]

I took it apart, no shocks, thank heaven. MAN there are lots of caps and stuff in there, along with a good heatsink, me happy :mrgreen: Now to identify the tranformers, since there's about 5 of them. How would I go about that?

[Peter Snowberg]

You won't find a 12V transformer or regulator in there. Sorry. Switch mode and linear supplies are totally different animals. (linear supplies are what you want for effects)

You have to be either slightly insane or a severe masochist to design switching supplies such as those. All the transformers will be custom jobs made to operate at very high frequencies. The output voltage is regulated by adjusting the duty cycle of the PWM that feeds power into the transformer primaries. (thus the term switch-mode regulation)

Any parts you can identify on the surface will be good for re-use, but don't count on identifying much in there.

Look at the datasheets for the LM3524 for more info on these beasts.

Take care,
-Peter

[smoguzbenjamin]

Well Peter I wasn't counting on anything much :mrgreen:

I have however found something neat, looks like a diode bridge type thingy. It has 4 legs, like this: - ~ ~ + Other markings are GI9536, that's it.

Is that what I think it is and will it take my AC and rectify it?

Plus, theres a heatsink in there which saves me buying one

[Peter Snowberg]

Yes... that's a good heavy duty bridge rectifier.

Switching supplies work by first making HV DC out of the mains AC. That DC is then chopped back into AC at a very high frequency. The high frequency allows the transformers to be TINY in comparison to the size required at 50Hz.

At the least you should be able to get that bridge rectifier, some HV caps, some low voltage caps, and some diodes out of there. Some of the diodes are probably dual units in a TO-220 package. As you mention, they're usually a good place to get nice heat sinks too.

Take care,
-Peter

[smoguzbenjamin]

Yeah I found some diodes packed in a To-220