ComputingYou will see this often

Desktop PC

Also called ATX tower, old computer, desktop case.

The highest-value carcass in ordinary e-waste if you keep the supply, the fans, and the case together. The motherboard is a poor source of identifiable chips and a decent source of hardware.

A donor is the dead machine. The parts below are what is still worth removing from it. “Leave it” is a part that is physically in there and should stay in there: too dangerous, too worn, or only useful as part of a repair you are not doing.

The wires that matter on a computer supply

Yellow is 12 volts, red is 5 volts, orange is 3.3 volts, black is ground. The supply stays off until the green wire is connected to a black one. Purple is a standby 5 volts that is present whenever the cord is plugged in, even if the fan is still. Unplug and discharge before you open the metal box.

Why it is in the trash while the parts are not

Slow, or it doesn't boot, or the disk died. The supply and the fans are usually fine. Bulged motherboard capacitors are a common silent killer on older boards and those capacitors are not the ones you keep.

Before you open it

Do this while it is still unplugged, cool, and not leaking. Unplug the IEC lead. The supply's primary capacitors stay charged. Purple 5 V standby is live whenever the cord is in, even with the switch 'off'.

Where the dead machine usually is

Home office — In the house
Office cleanout — Commercial
Bulk trash day — Curb
Move-out week — Curb

Office cleanouts produce them by the pallet. Ask before the recycler owns the pallet.

How it comes apart

Side panel off. Photograph the motherboard model if you might want the manual. Pull the drive whole — do not strip a hard drive on the computer bench, do it as its own donor. Bag the screws by thread.

Tools: Phillips, Meter, Flashlight.

What to take

The table is the short version. The notes under it describe that part inside this machine, not only the general description.

Parts in this donor
Part	Call	How many	How often	Where to look
ATX computer supply	Prize	1	always	Top or bottom of the case, IEC inlet.
Axial fan	Prize	1–4	usually	Front, rear, and on the CPU or supply.
Enclosure	Prize	1	always	The case itself.
Heat pipe	Bonus	1	sometimes	On a discrete graphics card.
Mains cord	Worth pulling	1	always	IEC lead.
Signal and hookup wire	Worth pulling	a harness	always	Supply cables.
Coin cell	Worth pulling	1	usually	Motherboard, near the southbridge area.
Heatsink	Worth pulling	1–2	usually	CPU, sometimes chipset or GPU.
Power inductor	Bonus	several	usually	VRM next to the CPU socket.
Pin header and connector	Bonus	many	always	Front-panel, USB, fans.
Screws and standoffs	Worth pulling	a bag	always	Throughout.
Electrolytic capacitor	Leave it	many	sometimes	Motherboard and supply.
Power MOSFET	Leave it	several	usually	VRM.

Prize

Prize — take this firstATX computer supply1 · always
A multi-rail supply. Treat the label wattage as a claim, not a measurement.
Top or bottom of the case, IEC inlet.
Four screws, unplug the harness. Keep the case closed if you will use it as a bench supply.
Often fine when the PC was scrapped for speed. Reject it if the fan is dead or the caps are bulged.
Prize — take this firstAxial fan1–4 · usually
12 V, 80–140 mm. 3-pin or 4-pin.
Front, rear, and on the CPU or supply.
Unplug. Do not salvage a screaming one; the bearing is the failure.
Good if the machine was quiet.
Prize — take this firstEnclosure1 · always
A steel project box with bays, a fan grid, and usually an IEC hole.
The case itself.
Leave the supply in if you want a powered box.
Dents do not matter. Rusted interiors do.

Worth pulling

Worth pullingMains cord1 · always
C13, usually 10 A class.
IEC lead.
Keep it with the supply.
Nicks and tape are a reject.
Worth pullingSignal and hookup wirea harness · always
Color-coded 12 V, 5 V, and ground, already terminated.
Supply cables.
Cut the connectors you will reuse and label them.
Insulation is usually still good.
Worth pullingCoin cell1 · usually
CR2032 in a holder. The holder is the part.
Motherboard, near the southbridge area.
Pop the cell. The holder desolders if you actually want it.
The cell is often near the end of its life. The holder is not.
Worth pullingHeatsink1–2 · usually
Aluminum or a heat pipe on a copper plate.
CPU, sometimes chipset or GPU.
Release the retention. Clean the paste. Do not cut a heat pipe.
Reusable if it is not bent.
Worth pullingScrews and standoffsa bag · always
M3 screws, standoffs, drive screws. 6-32 on some older cases.
Throughout.
Bag and label. Do not mix with laptop screws.
Good.

Bonus

Bonus, if you are already in thereHeat pipe1 · sometimes
A sealed copper pipe on the GPU cooler. Do not kink it.
On a discrete graphics card.
Take the whole cooler.
Good if it is not crushed.
Bonus, if you are already in therePower inductorseveral · usually
Shielded inductors, often marked in µH.
VRM next to the CPU socket.
Desolder only if you can read the mark.
Fine electrically; the value is the question.
Bonus, if you are already in therePin header and connectormany · always
0.1 in headers and the matching front-panel leads.
Front-panel, USB, fans.
Unplug first. Desolder headers only if you need them.
Good.

Leave it

Leave it — present, not yours to reuseElectrolytic capacitormany · sometimes
If the board died of capacitor plague, these are the evidence, not the harvest.
Motherboard and supply.
Do not collect a jar of them.
Suspect.
Leave it — present, not yours to reusePower MOSFETseveral · usually
Short house markings, not a catalog number you can trust at a glance.
VRM.
Leave them unless the full part number is printed and you use that part.
Unknown.