if you ever come in touch with an old power tool don't trash it, also if it's not working anymore.
Old tools were very simple in construction, but they also were built to last long. Since you will not find complicated electronics in them, you can disassemble them and look how they work. In most cases you will find out what is wrong, and fix it or ask to someone to do that.
In this specific case I found an old Italian brand electric sewing machine. Construction quality is great, very heavy and solid. At first sight it has a problem in electric wiring, let's see how to make a good repairing job.
Then we'll see that it also need some work on the motor.
Step 1: Fix the Wires
Wires are badly repaired and wrapped with package tape. When you see something like that don't try to connect the tool to the wall plug, if a shortcut will happen it can damage the tool and also your house network.
One way to fix it is cut the wires, and solder them together inserting them previously in shrinking tubes as isolation. but the best solution is to short the cable of all the damaged length, and make new connections inside the tool.
Step 2: Open the Case
This solution obviously obligates you to open the tool case, but this could be a good chance to look if everything seems ok before turning it on. You can also add oil or grease on all the mechanical gearing.
Usually you only need some types of screwdrivers, pay attention to use the right one, since you will be in bad troubles in case you strip the screw head.
At some stage of the disassembly you should reach the cables extremities. Stop here, don't open the contact screws before looking at the wire colours!
Step 3: Check the Connectivity
After writing a schematic with wires colours and corresponding plugs, you can open the contacts and extract the wires. In my case I need now to remove the clips, and I see that the wire is not the original one, so I have to write down a second diagram with the correspondence between two colour sets.
Finally you can cut the wires some inches before the clips, or you also can change the entire cable.
Step 4: Connect the New Cable
Now you can insert the shorted/new cable in the case hole.
You can be surprised but this is a critical stage... indeed I forgot to insert the shrinking tube! So remember that you can't do that in a second time, insert one or more shrinking tube pieces before inserting the wire.
Then you can connect all three wires to the correspondent screws. Close also a plastic cover if present.
Step 5: Assembling
After assembling all the covers, and tightening all the screws, is time to shrink your isolation tubes, which here are used to strengthen the wire and avoid it will wreck again in a short time.
I don't have the shrinking tube in the pictures, but I should have had it.
Step 6: Motor Turn
After fixing the power cable I turned the sewing machine on, and it worked. But pushing the pedal to obtain low speeds the machine didn't work, and some smoke came out.
With a further inspection I discovered that the commutator of the motor was not in good shape, and when powered, a lot of sparks were generated in that point.
Step 7: Repair the Commutator
So I had to open all the motor gauge to reach easily the commutator.
In the pictures you also see the motor brushes which are in most cases the reason that why old power tools doesn't work anymore. You can easily extract consumed brushes without dismantling too much, and you can find new brushes for cheap. Brushes are good in my case.
As you can see from the detailed pictures the commutator is a bit consumed, but not enough to need a complete rebuilding (see this instructable if you need to do that). I think that copper was spreaded from contacts to the adjacent ones, and electricity passes through the isolation.
I decided to scratch the isolation stripes with a thin screwdriver and then to polish all the contacts with sand-paper, and I obtained the result you see in second picture.
Step 8: Assemble the Motor
Before assembling the motor, check it and clean all the parts which are probably filled with dust and dirty, as the bush you see in the picture, which had the old exhausted filler in the cavity.
Assemble all the pieces back together, in the reversed order you dismantled them. Tighten all the screws, and add oil if you see rusted parts.
The sewing machine (and I hope every power tool you fixed in this way) is nor running great and I'm ready to make awesome project with leather and fabric!