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Hi,
It sounds like you are pretty methodical in working on this and from what I can tell it should be working for you.
I have read that occasionally this has happened before and after a few days of powering up the speedometer it will suddenly start working. The post I read said it was like two days later when he happen to look down and noticed the numbers had turned all by itself.
There is a circuit board in all of these speedometers that share an integrated chip. How it works is beyond me.
From what I can tell it looks for a pluse of a certain wave form and has to get a certain rate count going to divide it out before a step signal is sent to the odometer motor.
I have notice that when the engine is cranked the speedometer needle will jump up and fall back about the time the engine starts. I have often wondered it this is some sort of polarizing step or cycle.
Do you see anything like that happening? If so, then we know it's getting power to the cluster and half the speedometer.
I know Art has nailed down fixing these things on the speedo side and I'm glad he is working with you on this.
I'm aware he has thoughts about a 1215 chip and since he has knowledge to set these up on the bench to even check the speed side.
I have a need to ask if he has more notes on the odometer side?
I am curious about if he has a "work around" to trigger the stepper motor on the bench by itself or through the entire circuit board.
I have a signal generator and have often wondered if I could just twist up the right signal and inject it in some place.
I have one speedometer that either has a dead motor or 1215 chip. I have replacement chips but do not have the knowledge to check them out to see if they are any good. Short of trial and error,
Means doing something on a board and having to put it back in the car each time is too laborious for me to fix with only one '86 speedometer cluster in my collection.
I understand that the 92's are slightly different but mine still works and I hope I have spare in case mine bellies up like yours.
Maybe he can answer for both of us if it's possible that it could just suddenly start working, out of the blue, if one waits long enough?
A gear tooth falling out has been the latest reasoning to explain this phenomenon. I gather it's not so much only the electronics, except where capacitors are concerned.
What say you Art, got any clues for us to play with?
Phil
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