ATX power supplies, even dead ones, can have a whole host of recyclable parts hidden within them. Some of the usefull parts are right there looking at you.

Ok so we have a mains socket, a switch (sometimes not), a fan, a metal box and some wires.

What else is there?

Look at all the parts! There's capacitors, heatsinks, a big iron cored choke for the passive power factor corrrection, ferrite transformers (see how to recycle those here), transistors - both high and low voltage, diodes, resistors and more.

Often what has gone wrong with the supply, and hence what is broken, can be seen from just a visual inspection of the components.

The fuse is usually a good indicator of what's gone wrong. If it's blown, like this one is, it usually means bad things happened and there will be other blown parts.

If however the fuse is intact it can often mean that it is just a startup resistor or, more likely, an electrolytic or two that has failed.

As long as there are electrolytic capacitors there will be dead switch mode power supplies. Like most of the failures the two on the left are in the standby supply circuit.

While it isn't overly obvious in the image, the two failed capacitors have bulging tops much like two of the capacitors you can see here.

Visual identification like this is usually a dead giveaway of a failure but to test all the electrolytic capacitors that still look good you really need an ESR meter.

In any ATX power supply that has fan speed control you will usually find one of these attached to one or other of the heatsinks. Most likely, as in this case, the low voltage side diode heatsink.

This is a type of resistor whose value changes significantly with temperature and is used in this case to monitor the heatsink temperature. When the temperature rises the value of the thermistor changes and the fan speed control circuit makes the fan spin faster.

This is the most likely part to fail in an ATX power supply because it is usually left on all the time, even when the computer itself is off.

If you're lucky it will just be one or two electrolytic capacitors that need replacing but often the first sign that anything is wrong is when the switching transistor fails and blows the fuse.

That said you can often source enough parts from the rest of the power supply to get the standby supply to work. While the standby output is only a single 5V rail there is often also an internal 12V to 18V supply used to power the main switch mode controller circuit. This can make a handy low wattage supply for other projects.

There is usually at least one of these, sometimes with a different suffix such as LM431 or AZ431, in every switch mode power supply. It is the part that does the sensing for the standby supply output voltage regulation in ATX power supplies.

This is a very usefull part which I've put to work in other projects.

Where there is feedback across the mains isolation barrier there is usually one or more of these.

These are an LED and a phototransistor all in one opaque package. Current through the LED makes it shine on the phototransistor, this allows current to pass from the collector to the emitter just like any other bipolar transistor. The advantage here is that the LED and phototransistor are electrically isolated and no current will flow from one to the other even if there is many hundreds of volts difference in potential between them.

There are usually two high voltage power transistors that go to make up the main power half bridge switch. These can be bipolar, as in this case, or MOSFET and are often rated at 400V and 6A or more.

As it is usually the standby circuit that fails in ATX power supplies this pair of transistors are often good and can be reused.

The standby supply transistor usually isn't rated for the same current as the main supply transistors and may not even be a discrete transistor but a complete power control IC in a TO220 case, such as a TOP222.

You will usually find a few small signal transistors like these.

The transistors pictured are quite common and are 2SC945 equivalents. They can have a variety of prefixes before the 945 number but they are all the same 50V, 100mA, NPN transistor with an Hfe of around 200, very usefull for lots of circuits.

There is often a couple of PNP small signal devices as well, one in the fan control circuit and one in the 3.3V regulator circuit.

This is a special type of inductor that can be easily saturated and is often used in the 3.3V regulator circuit.

This inductor, along with the 3.3V filter inductor, is used as a type of magnetic amplifier to control the 3.3V rail voltage.

There are usually a few of these large size, low value, high power resistors scattered around the ATX circuit.

The ones here fulfill the minimum load requirement for the power supply and have been built into every ATX supply that I've ever opened up. Even the cheapest of them that omit every component they can get away with, like the mains filters, have them.

So if you're using an ATX power supply as a bench PSU then you don't need to add some huge ass expensive power resistors just to make it play nice. If it doesn't work without an external load then it is broken and needs fixing - or recycling.

Who doesn't need wires, lots and lots of not very long and not very short wires.

Black wires, red wires, yellow wires, orange wires, blue, green, grey and purple wires.

Wires!

Like the thermistor that is used to control the fan this one also changes value with temperature.

Unlike the fan control one though this one is designed to pass a relatively high current and have a relatively low value, usually less than an ohm, at the operating current. The relative change in resistance can be as much as 30:1 between its high, cold value and its low, warm value.

The diodes that make up the main bridge rectifier are usually high voltage silicon diodes.

These are your standard diodes with the standard 0.7V or so forward drop.

The diodes on the output side of an ATX power supply are usually paired high current schottky diodes in TO220, or bigger, packages.

There are often also a number of discrete schottky diodes used for the low current negative rails two of which can be seen in the lower left of this image.

These will have a much lower forward drop than silicon diodes, about 0.3V or so.