Desoldering a PSU Circuit Board

Making use of old junk is what I do best. Salvaging useful parts from old electronics and machines is a hobby I really enjoy.

In this project, I will show you how I desoldered several old PSU circuit boards I got from thrown-out computers in the junk pile at school. I will also feature the case/safe I built specifically for this operation.

I removed the metal hosing from the units that were very useful in my computer deskfan project and to make some of the drawers in my case/safe project. I have a total of 8 circuit boards to work with, but in this case, 'no pun intended' I will be focusing on just one.

To be safe working with a circuit board that uses mains voltage, the reservoir capacitors must first be discharged. To prevent electric shock, do not touch the underside of the board (shiny soldered metal contact) when holding it. Hold the board by it's sides or something sturdy such as the heatsink.

The mains/reservoir capacitors are the two large cylinders shown above. Think of them as storage tanks of electricity or as the name implies, reservoirs.

To discharge them, use a screwdriver to short the two metal leads together for each capacitor. If you see a large spark, that means that the capacitor still had a large charge stored in it in the range of 110V -240V dependent on the input voltage and may have been lethal if ignored.


Disclaimer:
This is not to scare or discourage you but, handling the circuit board can be very dangerous if the mains/reservoir capacitor is not first discharged. High voltage may remain stored in the reservoir capacitor even after being unplugged for a few years. Always release any residual energy that may be left in the capacitors by shorting the two leads together. You could get seriously injured or die if mishandled. I am NOT responsible for any injuries you may receive for failing to adhere to proper safety procedures.

Now that the board is safe to work with, the output DC wires can be removed from the board. To do this, use a cutting pliers to cut the wires as close to the board as possible. That way, the maximum length of the wires are saved and not wasted if they were cut say in the middle.

Now you would have salvaged the first component of the circuit board, the wires. It also makes working with the rest of the board a lot easier now that the wires are no longer in the way.

To desolder the circuit board, you will need a solder iron, preferably a powerful one, a solder sucker or solder wick comes in handy and at least something to hold the board steady such as a pair of helping hands. To help control the fumes, I used my fumes extractor feature of my case/safe and the also the help of my computer desk fan.

Once the circuit board is held firmly, you can begin to desolder. Start with one corner of the board first then work your way over to the rest of the board.

As you continue to desolder, use the solder sucker or solder wick to remove the melted solder from the joint. Doing so makes the components a lot easier to remove and more likely to fall out as you continue to desolder the leads.

Be careful not to hold the solder iron too long on any lead as this will transfer too much heat to the components and may burn them out.

A good technique I found was to remove a little solder at a time then allow to cool slightly then go again rather than to apply full heat for a longer duration to remove the solder that will risk damage to the delicate components. This is especially true of transistors.

In some instances, some smaller components will be destroyed by either severe heat or by mechanical force, i.e the smaller components refusing to budge and breaks by my forceful acting with the screwdriver.

This is what the circuit board looks like so far if you work from corner to corner.

Now then let's continue.

To desolder the transformer leads efficiently, I found that heating the leads and while simultaneously sucking the molten solder away works best compared to heating, removing the iron then suck away.

Also using a screwdriver to pry away the transformer while heating the contacts makes removal a breeze.

There is just one more lead holding the transformer on (picture on the left). Sometimes the metal contacts from the circuit board is pulled out on the transformer leads, so to remove them, just use the heated solder iron to push them off.

Further progress!!

Time to remove the heatsink. This one is screwed to the transistors and held to board screws. Easy removal.

Sometimes there are other components that are adhered to the heatsink such as this thermistor that needs to be pried off before removing the heatsink.

This heatsink will be most useful later.

Now for the next half of the board.

This is one of the IC chips that was screwed to the heatsink. This component was removed with relative ease. The desoldering process continues until the entire board is desoldered.

This is what the board looks like with all of the components desoldered.

Time for Sorting and Storing the Components

The nifty thing about the case/safe is that it has a lot of storage space in a wide range of disguised compartments. For example, I use the uppermost 5 1/4" compartment to store mainly the IC's and transistors of any other semi-conductors.

I also palce a few breadboards in there for safe keeping.

All the semi-conductors and IC's are sorted and placed in this drawer.

The next drawer below stores mainly the resistors and switches.

Lots of goodies!!!

The capacitors are stored in the third drawer.

These are electrolytic capacitors both small and large.

The inductors are stored in the floppy disk drawer.

The much larger transformers could only hold in the much larger 5 1/4" compartment.

Well, that's a rap. Time to pack up and power down the fans.

I hope you found this project useful.


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Computer Case Safe/PSU Combo Based Projects