Recently, my Mag 77 Skill saw suddenly stopped working. I made a cut. I put the saw down (gently), and when I picked it up, it sputtered for a second and stopped. I hit the switch again. It sputtered slightly again, and that was the last sign of life from it. Luckily, I have another older saw, so I finished the project with that.
I was just going to buy another saw, but when I saw that the price tag on this saw model, which Skill still sells was $189, I figured it was worth the trouble of trying to fix it.
I framed houses for about three years when I was (much) younger. We used these worm drive Skill saws exclusively. They are beasts. They can take ridiculous amounts of punishment. I have seen them fail, but it usually comes on gradually and involves the triggers or brushes. However, I use this saw so rarely, it seemed highly improbable that it would be either the trigger or the brushes. Nevertheless, I inspected the brushes and tested the trigger, and you should too.
Neither of these was the culprit here. So I had to dig in and crack the case. It’s actually quite easy to get into the motor on this saw. The only caveat is it uses T20 torx screws. I had a driver laying around, but if not, you are going to have to buy it. There are some larger Torx screws on the case, but you don’t actually need to pull them in order to get to the motor.
Before you begin pulling the screws, you should remove the brushes if you have not already done so. They are removed by unscrewing two black plastic plugs from each side of the case. You can see a picture here of one of the brushes that has been removed. Notice that I damaged the cap slightly in the process. Use a screwdriver that fits well. They are a bit delicate.
Notice that the brush is quite long. This brush is barely worn. If you use a saw heavily, you can wear out your brushes. So if need be, you might have to replace yours. You risk damaging the brushes if you pull the saw apart before you remove them, and you absolutely cannot put it back together without taking them out anyway as they are spring loaded and will pop in and block the motor armature from going back in.
You need to pull these five screws (green arrows) to get the saw apart.
You can see three of them here, and the other two are on the back side. The four that go into the back of the case are very long. Notice that small part marked with the blue arrow. That fell out of somewhere at some point. After studying the saw a bit, I decided it must be a tensioner for the motor armature. I’ll show you where I put it when I was reassembling here in a second.
Once I got the saw apart, I saw the problem immediately. There were two wires not connected to anything. It was obvious they had been connected together, but had broken. Unfortunately, it occurred to me to write this up after the fact, and I didn't take a picture of it. They had been arcing to the case for some time before the saw failed.
If you look at the picture of the cooling fins, you can see the electrical arc damage on them.
This explains why this saw had been popping the GFI for about a year before it failed. I had gotten in the habit of just plugging it inside because the outdoor GFI plug would just trip every time I tried to use it.
What happened was the manufacturer ran one of the supply wires to the forward end of the motor and connected it to the enamel coated wire from the windings. They taped the two wires down with strapping tape. The strapping tape failed after a few years, and the wires were long enough that they eventually pulled away from the windings far enough (or maybe got sucked into) the cooling fins. When they started shorting to the fins, it caused the GFI to pop. And eventually the mechanical strain of hitting the cooling fins eventually broke the connection causing the saw to die.
The fix was very easy. I cleaned up the enamel coated wire with some sandpaper, and I soldered it back onto the supply wire. I then taped the connection with electrical tape, and then I taped that to the windings by threading through the electrical tape through the loops using a paperclip. I put the saw back together, but I still wasn’t feeling too good about it. Then it occurred to me that what it really needed was a more positive non-conductive fastener like a zip-tie (Panduit). So I tore the saw back apart, this time not removing any unnecessary screws, and that’s when I also decided to photograph it.
The final work looks like this. Notice that I didn't clamp the zip-ties directly on the wiring. They are sitting on electrical tape. I was a bit concerned about vibration causing them to damage the enamel on the windings. I think it's probably better to not to tighten them down directly on the windings. And I snugged them, but I didn't really zip them down as tight as I possibly could. Maybe it would be better to just tape it. I really wrestled with that decision before deciding to use the ties. But I don't trust that electrical tape not to fail after a couple years. And it's very hard to thread it through the windings. So two turns was about all I could get per piece of tape.
The saw now works perfectly, and it no longer pops the GFI.
No comments:
Post a Comment