I had a bay fan from an older computer that I need in another project. Unfortunately the PCB design was pretty poor and it had one of the paths right next to a screw which allowed a lot of flex on the board. That led to the board cracking and of course the circuit being broken. So this instructable is to show one way to repair a broken PCB.
Step 1: Tools and Materials
1. Soldering Iron (I recently picked up this little battery powered one pictured and love it except you have to hold a button down for it to be on and that causes some hand fatigue/cramps for old guys like me otherwise fantastic)
2. Emery board (if you don't know what this is ask your wife, girlfriend or mother whichever is appropriate or just use some fine grit sandpaper)
3. Bright flashlight (I have a little LED one that I use constantly pictured here)
4. Helping hands would have been great though I don't have a pair they make life a lot easier.
5. A drill or a sharp point knife (not pictured)
6. Multimeter (optional though suggested)
7. Breadboard (really depends on what you are repairing I used one to test my circuit after but you may not need this at all)
1. Solid core wire (you could use a bridge or some other piece of wire just solid core copper was handy and easy)
3. Clear nail polish or some other coating to cover the bare copper when done (optional)
4. Flux (I didn't have any but it would have been handy to have)
Step 2: Identify the Connection Needed
The first thing to do is to determine what that path was attaching. Looking at the board just eyeballing it I first thought that the path was to the +5V wire. That was not in fact the case which is why you need to take some time and trace the paths to know what they are connecting. You don't want to connect it to the wrong place and create a short or cut out another path of the circuit. One thing that is helpful in this is to use a fairly bright flashlight and put it on the other side of the board as to the one you are viewing. Look at the pictures and you can get an idea of what I mean though they don't really do it justice. It really lights up the connections and makes it easy to trace them.
So in my case I determined that the broken connection was a ground rail and that the +12V and +5V ground wires were connected so I just needed a decent clear spot to connect the ground wires to the ground path.
Step 3: Prepare the Board to Bridge the Break
Once you have identified where you want to make your bridge take your emery board (or very fine grit sandpaper) and very lightly sand off the coating on the path as shown in the picture above. You will see some exposed copper and this is what you want. Be careful not to sand to hard or to much as you just want to expose the copper to get a connection with your bridge.
Next take your drill (the bit size will depend on the size of wire you have) and make a hole on the very edge of the path/s or beside the wires you need to connect to. In my case you can see I had one path and one wire to connect to. I used a pocket knife that has a sharp point to make my hole as I didn't have a small enough bit for my dremel at hand. Using a knife just firmly but not forcefully press the knife into the board and rotate clockwise then counter clockwise keeping the point perpendicular to the board. About half way through you may want to switch to the other side to keep the hole small if you are doing it this way to avoid the width of the blade digging an ever widening cone into the board.
Step 4: Wire and Solder
Next you want to take your wire and strip one end.
Put the striped end of the wire in one of the holes.
Bend the wire to the other hole and mark that spot on the wire.
Cut the wire a bit further up from the mark.
Strip the wire from mark exposing that end of the wire.
Put that end of the wire in the other hole.
Now bend these leads sticking through and try to make the best contact you can to the surfaces/components to be joined.
Now solder your wire to join the path or wire, component or whatever else you needed to bridge.
I didn't have any flux but it would have been a good idea to use. Also make sure when you are soldering that you heat your wire bridge and the path too so you don't end up with a cold joint.
Step 5: Testing and Finishing Up
At this point it would be a good idea to use a multimeter and test continuity. To do this set your multimeter to continuity test (the little buzzer looking icon) and touch the exposed path and the other side of the the connection. If you hear a buzz congratulations you have bridged your broken pcb.
I didn't want to break out a PSU and connect up the molex to test my connection so set up a breadboard test using 9V and 5V. I used an LM7805 to provide the 5V and another 9V battery to connect to the 12V (since it has a pot on there didn't really need the full 12V just a voltage difference to test the circuit).
Once I was finished testing and knew I was in good shape I clipped the excess wire off and added some of my daughters clear fingernail polish on the exposed PCB path to keep corrosion off the copper.
Step 6: Additional Thoughts
Keep in mind that the wire you are using is probably going to add some resistance to the circuit in most circumstances this is not likely to be a big deal but it's worth noting.
Be careful not to create a solder bridge if you are working close to other components etc.
Hope this helps someone. Please vote for it in the "Fix it" contest if you found it helpful.