Introduction: Mailmate Shredder - Replace the Internal Fuse With a Circuit Breaker
After some heavy use last year during tax preparation, the internal fuse blew. So I went to get a replacement. It took some time to find out how to open up the shredder, but eventually I got the job done and the shredder worked again….
…until I prepared this year’s tax.
The fuse blew again, and getting the shredder open just consumed so much time the first time that I decided to replace the fuse with a resettable circuit breaker.
I could have just bought a new shredder and I really was on the verge, but I really love my Mailmate.
It also saves about 37 bucks (the price of a new shredder minus the circuit breaker) and it is environmental friendlier to repair than to replace.
So this time I’ll show you how to open the shredder and how to replace the internal fuse with a circuit breaker.
If you have other appliances including a hardwired fuse, this instructable may help getting an idea on how you can improve the affected appliance.
Warnings:
- Be careful if you follow this instructable and only do this if you are familiar working on electronic circuits.
- The shredder runs on AC, so ensure to pull the plug before opening the unit.
- The circuit board has some capacitors which could carry load. If not handled properly you run the risk of an electric shock.
- When handling the internals of the shredder, be careful with the blades inside to prevent cuts.
- Also, the sticker on the bottom of the shredder’s top indicates that the unit is not user serviceable.
- Do not wear your best clothes. The gears inside the unit are lubricated with some nasty grease.
If you follow this instructable anyway, you do so at your own risk.
Step 1: Tools and Supplies
- Screwdriver
- Soldering iron
- Desoldering pump
- Solder
- Heat shrink tubing
- Cable lugs
- Electrical pliers
- Cable
- Cable stripper
- Circuit breaker (5A as per PCB, anti-surge type)
- Electric drill
- Saw
- Wrench
The screwdriver must be long enough to reach the screws which fasten the waste bin housing to the shredder top (about 6 inch, maybe a little more).
The screw heads are all Phillips recessed heads. As I couldn’t find a screwdriver with the appropriate length, I used a regular flat head screwdriver which was long enough and filed the size of the blade to fit the screws.
The cable must be long enough to connect the main board with the circuit breaker. I used a cable with a length of about 12 inch and later shortened it to the appropriate length.
You can use single conductors, but as space is sparse within the shredder head, I opted for a two-core cable which makes routing the cable through the unit easier.
The wire cross section should be similar to the mains cable’s cross section as it has to carry the same current.
The internal fuse is rated at 5A. Unfortunately, I couldn’t get a circuit breaker with the same rating. So I bought one being rated at 6A. I assume that this will still work in the long term. It’s at least better to give it a try (in my opinion) than to open up the unit every time the internal fuse trips.
Step 2: Separating the Shredder Top From the Waste Bin Enclosure
The shredder top sits on top of the waste bin enclosure and is held in place by two Phillips screws.
The screws can only be accessed through the bottom of the waste bin enclosure. They are located underneath two of the shredders feet. The feet are glued to the base with double sided adhesive tape which you may have to replace, depending on the age of the shredder.
Once you peeled off the feet at the base, use a screw driver which is long enough to reach through the waste bin enclosure up to the shredder top.
To finally remove the shredder top from the base, use a flat head screw driver and carefully pry away the stainless steel plated front panel which sits right above the waste bin. It is fixed to the shredder top utilizing double sided adhesive tape.
On my unit, the tape did still stick well enough in the end so that I didn’t have to replace it (again, depending on the age of your unit, it may be necessary to replace the tape).
After loosening the front panel, you can just lift off the shredder top.
If the stainless steel plated front panel got bent too far while prying it off, you can easily bend it to the other direction. This way you ensure that it sits tight to the shredder top once you reassemble the unit.
Step 3: Opening the Shredder Top
Up until now, nothing really dangerous or harmful could happen.
In this step you will open the shredder itself.
So I want to point out again that you are now working in and with the area of your unit where you could possibly cut yourself at the shredder blades or that you run the risk of an electrical shock if you are not familiar handling electronics.
Always remember, safety first!
Every time you remove a part from now on, be careful that you don’t strain the cables from and to other parts too much. They could come lose from connection points (on cable lugs or solder joints) later, causing a potential risk of electrical shock. Before reassembling the whole unit, check any connection to ensure safety.
Again, use your long Phillips screw driver to remove the 6 screws of the shredder top.
Be careful not to lose the screws along the way as they tend to remain in the deep holes of the housing.
If you use a magnetized screw driver you'll probably get lucky and can fully remove the screws with the screw driver. Otherwise you can just turn the unit upside down so that the screws drop out of their holes.
Lift the bottom part of the shredder top from the top cover and remove the strain relief of the mains cable from the housing.
If you want to work more freely you can remove the safety switch in the bottom part of the housing. But if you do so, remember to reassemble it properly once you put the unit back together again.
If you forget to put the switch back in, your shredder won’t work (the safety switch checks whether or not the waste basket is inserted in the unit to prevent you from accidentally touching the shredder blades while the unit operates).
If you remove the safety switch, ensure that you check its proper function after reassembling the unit. It could happen that the switch gets jammed during its installation rendering it useless. In this case, the unit would operate without the waste bin which can be potentially dangerous to you, little kids or pets playing with the unit.
Step 4: Get Access to the Circuit Board
This step may get a little messy depending on where exactly you grab the motor and shredder assembly.
The motor and gears are lubricated with some nasty grease. Don’t remove the grease if you don’t have a similar viscous grease at hand to replace what you removed.
Lift the motor and shredder blade assembly from the top cover of the housing.
Be careful not to cut yourself. The blades can be sharp.
Remember the position of the shredder assembly within the housing cover. You have to reposition the assembly at exactly the same place when putting everything back together.
Step 5: Remove the Circuit Board and Prepare for the Circuit Breaker
Remove the two screws which fasten the PCB to the housing cover.
The fuse in the picture already was a replacement in my unit. The original fuse was way bigger, similar in size to what’s printed on the circuit board.
Desolder the fuse using the soldering iron and the desoldering pump.
Prepare the cable for the circuit breaker by stripping the cables and pre-tinning its ends.
Stick each of the cables through one of the drill-holes of the PCB where the fuse was soldered in and solder the ends to the PCB.
Cut off any excess cable to keep the soldering joints as low as possible.
The upper left cable is the one directly connected to the mains supply (if looked at the PCB from the back / right beside the blue mains cable when watched from the front of the PCB). Remember which cable is running to this connection. The circuit breakers connectors are named “Line” and “Load” (at least in my case). So you want to ensure to connect the cable coming directly from the mains supply with the “Line” connector.
Replace the PCB to the housing cover and attach it with its two screws.
Don’t attach the cable lugs for the circuit breaker to the other end of the cable just yet. First install the circuit breaker in the bottom part of the housing so you can better estimate the needed length of the cable.
Step 6: Install the Circuit Breaker
Within the shredder top there’s only little space for positioning the circuit breaker. It cannot be mounted too far to the top as it could possibly collide with the housing cover later.
There’s also a lot of space already taken by the motor and shredder assembly. This only leaves some space for the circuit breaker right beside the screw dome facing the motor.
To ensure I can actually reassemble my unit, I eyeballed the distance of the circuit breaker’s center to the rim of the bottom part of the housing and the distance to the screw dome.
Mark this position and drill a hole with the appropriate size for the circuit breakers thread.
Pre-assemble the circuit breaker and lightly fasten it with the nut that came with it.
You cannot fully install the circuit breaker just yet because the shredder unit slides into the waste bin housing. So you first need a cut out in the waste bin housing to accommodate the circuit breaker's thread.
With the bottom and top part of the shredder housing lying side by side, shorten the cable you installed in the previous step to its appropriate length.
Strip the cable ends and attach the cable lugs.
The cable lugs must be the proper size for the circuit breaker’s connectors on one side and the wire cross section on the other side.
Check that the lugs are attached to the cable properly by lightly pulling on them.
To ensure that no metallic part of the connections can touch any other live or housing part within the unit, attach heat shrink tubing to the cable lugs to prevent the risk of electrical shock.
Connect the cables to the circuit breaker ensuring a tight fit.
Step 7: Reassembling the Shredder
Replace the motor and shredder assembly into its recess within the housing cover.
Like described previously, be careful not to cut yourself and remember that the grease is very nasty.
Put the bottom part of the housing on the top cover.
Ensure that the circuit breaker and the cable running to it from the circuit board don’t get damaged. The space is very tight.
Replace the mains cable strain relief into its recess.
Ensure that the shredder output of the motor and shredder assembly properly aligns with the opening of the bottom part of the housing.
Fasten the bottom part of the housing to the housing cover with its 6 screws.
Slide the shredder part of the unit onto the waste bin housing until the thread of the circuit breaker sits right on top of the rim of the waste bin housing.
Mark the position of the circuit breaker and make two cuts to either side of the thread into the waste bin housing.
Once your cuts are deep enough to allow the shredder top to fully slide into the waste bin housing, use a pair of pliers to break off the excess plastic.
Carefully remove the nut of the circuit breaker. Don’t push the circuit breaker into the shredder housing.
Fully slide the shredder top into the waste bin housing, attach the marking plate and replace the nut carefully.
Replace the screws which hold the shredder top and the waste bin housing together.
Test run the shredder with the waste bin inserted.
Remove the waste bin and try again.
The shredder should not work without the waste bin.
If it does, check if the safety switch got jammed during reassembling the unit.
Fix any faults before using your shredder on a regular basis.
If everything works, you now have a Staples Mailmate with a resettable circuit breaker. No need to replace a fuse any more.
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