Techno Stuff
How They Work - Index Units
Indexing a ratchet is a little different, as there is not really a home position for the ratchet. In this case, all the index unit is doing is stopping the ratchet from turning. As usual, sometimes the default state of the unit is to stop the rotation (e.g. spotting index unit keeps spotting wipers from turning most of the time). Sometimes the default state is to let the unit turn, which is the case for the search index unit below.
miscellaeous parts |
| search ratchet not indexed |
|---|
In this pic, we are looking at the control unit from the motor end, and the search index contact plate is removed, so we can see the wipers. The picture is rotated 90 degrees. The search index unit in it's inactive state allows the search ratchet and wipers to turn.
miscellaeous parts |
| search index unit active |
|---|
OK, here we have detected a winner and payout is supposed to happen, so the search index coil is turned on and the pawl (relay plate) is engaged in a tooth on the ratchet, stopping it from turning. As you can probably guess by the shape of the teeth on the ratchet, the ratchet is rotating counter-clockwise when viewed from this end of the control unit shaft.
What I'm not showing you is the entire index assembly. The portion I'm holding there is the coil, pawl, and mounting bracket. That assembly bolts onto a frame similar to the one on the preceding page. Notice the elongated holes in the top and bottom of the pictured bracket. These allow the bracket assembly to slide up/down on the index frame. The correct position is make sure that when the relay plate is sitting down on the top of the coil, the pawl is all the way engaging a tooth.
In other words, loosen the bracket enough so it will slide, shove it all the way up then press the relay plate down into the top of the coil to cause the bracket to slide back down (making sure the pawl is going all the way into a tooth). 'course, the index unit is sometimes hard to get to - you usually need to unbolt it from the plate it's sitting on and take out out enough to access the bracket screws.
If the relay plate is not able to sit squarely on top of the coil because the bracket is too high, the index unit will buzz when powered.
Sometimes the index unit is has an additional screw adjustment which
limits the amount of up-travel on the relay plate. For timing
critical units like the search index unit, you want the pawl to be
almost touching the ratchet teeth when the relay is not powered. This
makes indexing the ratchet as fast as possible since the relay plate
doesn't need to travel very far. However, there's switches on the
assembly, and less travel means the switch contact gaps are smaller so
you have to watch their adjustment and condition.
