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Hi Phil,
When you cite the internet reports of the odometer starting to work after some length of time, I imagine these stories to be evidence of the cracked solder sort of poor connection being influenced by variations in temperature and vibration. We have a TV which occasionally needs a good slap on the side (yes it still has a side).
It also could be that errant cog tooth. It's in there if it hasn't been removed, so why not be careful, and find it?
The 2115 chip does not fail unless we make the mistake of putting the tach wire on the cruise terminal. The symptoms vary as a result of the high flyback voltage from the coil. Sometimes the zap is enough to kill both speedo and odo functions; some report only one of the odo step motor driver transistors shorts out and the speedometer continues to operate. An ohmmeter will confirm the transistor is shorted.
Also, saying "reflow" is a fairly well-understood term to those experienced in electronic repairs, but the practical result of this by a novice can be less than effective. Ask David Samuels. Not everyone comfortable with engine or rear axle swaps fits this "pocket protector" type work.
You ask if I have a workaround for checking the step motor. An ohmmeter can check the motor. It is just wire. No brushes, just wire. A motor can be damaged, but only by someone trying to repair the odometer and making the mistake of connecting the tach wire to the cruise terminal, causing the chip to short, and then operating the unit with the chip transistor shorted for long enough to cook the insulation on the motor windings. It can also be damaged by overheating the pins (they are inserted into polystyrene) causing them to move and break the fine wire of the motor winding inside. Dave hasn't said whether the tach wire was misplaced, and he hasn't posted a photo of his reflow work.
You also speak of the "laborious" trial and error work. Testing. Of course, the first time I did this, it was on the bench. Somehow I knew it wouldn't be the last time, having 5 cars with the same gauges. And, I also knew others would not have signal generators, bench supplies, and oscilloscopes poised for car repairs, so I put this photo sequence together. I suspect some of us could wrangle up something similar in less time than it took for you to write your post last night.
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Art Benstein near Baltimore
When everything's coming your way, you're in the wrong lane.
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