Reviving Dead MailMate Shredder

Here is one way to inexpensively bring a shredder into your home office!

I always wanted to get a shredder to dispose of sensitive documents, so when I stumbled on  an ad for a broken shredder to give away, I jumped on the occasion!

Basically, the electronics inside were shot, but the motor was in perfect working order. The simple fix is to make a basic circuit that will run the motor forwards and backwards.

This is my first published instructable, yay!
The downside is that this project was done way back in February 2010, and the first steps were not documented with photos... let's say that I hadn't quite grasped the mindset of photographing for instructables yet...

Materials needed :

DPDT switch
On-off switch - optional if your DPDT switch has an off position
Insulator for some connections - heat shrink, electrical tape, marettes...

Tools needed :
Crazy long philips screwdriver - I used an 8 inch #2, but it was tight, so maybe a #1 would work better
Cutting pliers
Soldering iron and solder - recommended, but it's possible to do without.
Dremel - again, recommended, but it's possible to use other cutting tools

Step 1: Open It Up!

First thing to do is to find the hidden screws under the feet. The feet are the foamy adhesive type and are hard to remove without trashing them. Had I known better, I would have just made a hole through the foam to get to the screw after felling for a depression in it with my finger. Especially since that part of the foot doesn't support anything. In addition to being hidden, the screws are very deep, and this is where the super long screwdriver comes in handy. After the screws are removed, it takes a bit of muscle to pop the top off, giving access to the guts.

Step 2: Gut the Beast and Evaluate What You Can Do With What You Have.

In my case, I had no clue as to what was broken, so I just removed the circuit board and cut the wires as close to the board as possible, in order to give me some room to move later on. I of course kept the board for any salvageable components in a future project.
Apparently, this shredder came in a version with an AC motor, and a version with a DC motor. I have my doubts about reversible AC motors... correct me if I'm wrong, but nonetheless... When taking out the motor, check for a sticker with the specs. In this case it's a 120V DC motor. Note that there are 4 wires coming out of the motor,and two of those are obviously the DC power wires since they are black and red. The other two are blue, and from what I can tell, they are probably from a sensor of sorts, since there was an overload LED on the cover.
The fact that this is a 120V motor can be considered a good thing, since no transformer will be needed in the new circuit. We now also know that we need a way to convert 120V AC to 120V DC. 
Enter the magical world of rectifier bridges! 

Note : the actual voltage from the outlets in your home may vary.

If you dig a bit deeper, you can find a micro switch that cuts power to the unit if the bin is removed. Leave it be. I won't talk about it either in the following steps. Just remember that it's part of the AC wiring.

Step 3: Learn About the New Heart for Your Monster

Ok, so now I know that I need a bridge rectifier, but what is it exactly?
Well, it is usually an arrangement of 4 diodes that will act like traffic cops, directing all the electrons going in one direction to one wire (the negative, normally black wire), do their loop on the circuit, and come back through another wire (the positive, normally red wire).
There are 3 popular diode arrangements to make those bridges. It can be simply 4 diodes soldered on the circuit board, or it can be an integrated circuit taking the form of an upright rectangle with a beveled corner, or a square unit that lays flat on the board.
The rectangle type usually have the AC come in the center pins and the DC out of the outer pins, with the positive towards the beveled corner.
The square one has the AC come in opposite corners and the DC out of the other two corners, just like you would see in a circuit diagram.

The one I got for this project is the square type. I guess this design is more popular with higher voltages.

You can check out this Wikipedia article for more detail and some pictures.

Step 4: Find a Way to Control All That Power!

Now that we have DC, we need to be able to get the power to the motor, to be able to turn it on and off, and be able to reverse the motor in case of jams. So, an on-off switch and a mechanism to reverse the polarity of the DC current...
The reversal mechanism can be easily designed around a double pull double throw switch, known to friends as a DPDT switch. It is a switch that can control two different circuits from one power source. Some have two positions, where one circuit is closed (on) and the other is open (off) at all times, known as an "on-on". Others have three positions, on-off-on, where you can have either one one of the circuits closed, or both open. If you have the latter, it is the cleaner option, since that type of switch acts both as the reversal mechanism, and the on-off switch. The former is the "more switches looks cooler" approach, which I chose. On top of that, It allowed me to recycle an on-on DPDT switch I had lying around.

I believe that there might also be a type of off-on-off switch, where both circuits are normally closed, and tipping the switch would interrupt one of the circuits, which would be useless for this project... unless you want to make it overly complicated and energy inefficient by using normally closed relays... o_0

Step 5: Modding the Case and Mounting Stuff

So, I went with the "Mount stuff first, wire later" approach. I simply reused the holes for the power and directional buttons, for the same funtions...

Some dremmel action action was required to make the new switches fit. See, the original switches were momentary switches, and needed the complex circuitry to work. My simple circuit needs different kind of switches to emulate the complex circuit, so I chose a big red button of doom for the on-off switch, and the voltage selector switch from a dead power supply for the directional switch.

Step 6: Circuit Design

Since there is only 4 components in this circuit, we just need to find out how to solder wires between the components. Forget about circuit boards,this is supposed to be a simple project after all...

The trickiest part here is the reversal mechanism, which revolves around the DPDT switch.
So, we get DC to the middle pins of the DPDT, and then what?
The cleanest way to connect the two sides of the switch to the motor is actually to connect the tho sides of the switch together, connecting the positive tab of one side to the negative tab of the other side and vice-versa, crossing the wires*.  Then connect the wires from the motor to either side.
In my design, I chose to put the on-off switch on the negative wire, between the bridge and the DPDT switch. It could also be put on the red wire in the same fashion.
A fuse could also be placed in line on one of the wires before the bridge and is highly recommended for the protectionists out there. 


*Some switches come pre-wired like this, made specifically fore pole reversal, with 4 terminals instead of 6. Two for the input, and two for the reversible output.*

Step 7: Testing

Well, now that everything is soldered in place, you want to run this beast a few minutes to see if anything burns out... make sure that you run it in both directions.
On my setup, I have to power it off before reversing polarity, since there is no off position on my reversing switch. My one and only attempt to do a live reversal only concluded in the motor stopping, and there is the possibility that this procedure could hurt something in the circuit if executed repeatedly. Your mileage may vary.

*IMPENDING WARNING*

You can enjoy the fact that the shredding blades are all exposed, so BE CAUTIOUS, don't put anything in there, or near there, or attached to something you might regret going in there!!!  

Step 8: Put It Back Together and Enjoy!

Now that everything works, just tuck the wires in, close the lid, put the screws back in, and enjoy bringing doom to countless documents!

There is also a low quality 6 second clip of it in action - if you insist.

Step 9: Things I Have Learned From This.

I have learned to easily identify rectifier bridges in circuits, and I now know that if one of those is present at the beginning of a circuit, it is total nonsense to have a polarized plug for this device... gosh those protectionists... I might extrapolate that having a polarized plug is nonsense for all AC appliances, but then again, there is a distinction between the 'live' and 'neutral' wires...

I took many pictures when I did this hack, but frankly, I had no Idea what kind of pictures would be handy for an instructable! Now I know a bit better :)

Finally, as part of the learning process of making instructables, I would like to hear any positive suggestions on the structure of this instructable!