If your Model 28 Teletype does not start at all, the lights come on but there is no movement, it may be as simple as pressing the reset button. This is a Model 28 Wall mount with a unique motor layout, so yours may be elsewhere, but it will be near the motor itself.
Unfortunately, they placed this reset button in a very inconvenient location, so reaching it will require some disassembly.
If your Model 28 frequently requires this reset, or experiences motor bounce or weak start then it may be the starting capacitor. If you turn on the machine and you can observe the motor shaft bouncing back and forth, but never making a complete revolution is describing what I am calling motor bounce. A weak start is where the motor can make a full revolution, but it takes awhile to get there then spins up to speed slowly is what I am calling a weak start.
Capacitors do have a life span, and while these machines are incredibly durable, as evidenced by this machine still working, capacitors can wear out over time. The startup capacitor gives the heavy motor a kick to get it going from idle, and in normal operation the Model 28 will instantly spin up from idle when turning it on.
Teletype Bulletin 295B or 570-220-100TC-6503 have descriptions and diagrams of various Model 28 Teletype variants (found at http://www.navy-radio.com), but Bulletin 295B has some part numbers for the startup capacitor. You may find these either by asking at the Greenkeys mailing list, or from Mr RTTY http://johnwhitney.com/misc/paul-rtty.htm.
On my machine I found it was easiest to move the motor mount to get access to the startup capacitor. Not difficult, it was just 4 large machine screws. I did have to slip the belt off by removing tension on the belt which requires loosening three tensioning screws.
The startup capacitor is friction fit in place, I found channel locks worked to (gently) lift the clamp so the old capacitor can be removed and the new one put in place.
The replacement capacitor had beautifully attached spade terminals, but I opted to clip them off since I want no possibility of those terminals touching something and shorting. I opted to join the wires with solder and shrink tube them together. There are no orientation markings on the old or new capacitor, and it is AC, so orientation is not important from what I am reading. I put some silicone on the leads end of the capacitor to give the somewhat delicate connections some reinforcement and to prevent anything from shorting the capacitor out.
After replacing the capacitor I have eliminated my machines tendency to trip the cutoff forcing me to reset it often, and the motor no longer tends to bounce more often than not on startup. Startup is nearly instant and strong, which is what I have found to be normal in viewing videos of other peoples Model 28 Teletypes.
