Reviving an old post.
76zimmer was kind enough to pack the offending machine up and send it to me, so I would not wonder for years what the heck was wrong.
Of course, when it arrived, everything started popping and I was unable to examine it.
Finally got a chance to look at it briefly today.
Box was in good shape. The only damage was from the end of the screw drive sticking out the end slightly when the machine shifted in the box.
Upon taking the cover off, I was surprised at what I found. Instead of a spring loaded switch which got tripped when the door hit something, or a current relay of some kind, it uses a reluctor wheel and detector similar to the pickup in an electronic distributor.
I have not had time to work out the circuit, but I'm sure it works on a "missing pulse" system.
There is an adjustable clutch between the drive screw and the motor. The wheel is on the driven side.
When the drive screw stalls out, the clutch slips and the pickup stops sending pulses to the board.
The detector usually works on a fast timer system. When the motor turns on, an electronic timer starts.
When a pulse from the pickup arrives, it resets the timer. As long as a pulse occurs before the timer times out, all is well.
If the timer times out, then something has gone wrong, and the motor is reversed.
There are a couple of possibilities as to what is wrong here. Normally I would suspect that the gap between the wheel and the pickup might be just on the edge of too far. But, this unit ran a long time with no problems, plus it only occurred when the door was hooked to the machine.
I shook the shaft to see if there might be some bearing wobble that might cause the gap to change under load, but it was solid.
Which leaves two ideas.
Either the timer has changed due to a leaky capacitor on the board, and when the motor sees a load it is slowing down just enough to let it time out, which is possible.
Or, and the one I like best, is that the motor capacitor has gotten weak and is causing the motor to run slower than usual.
Won't know for sure until I can rig up a test jig, but I wanted to post the first impressions and pictures.
I pulled the safety board off to examine it, which is why you see the unplugged connectors.
I'm going to be tied up for a while, tax stuff, an auditor, and the annual meeting of the company I am co-manager of will be keeping me busy until the end of the month.
And at the end of the month my "nephew" comes home on leave from Afghanistan, so I need to spend some time with him.
But I can't wait to find out what is what.
Thanks to 76zimmer's meticulous job of including parts, I may mount it on the door to my storage shed when I get it going.
