Odometer stepper motor twitching, not spinning...

[nrubenstein]

So, I'm attempting to repair a VDO speedometer, but I just can not get it to drive the odometer.

Here's what a good one (aside from all the missing teeth on the gears) looks like:
http://youtu.be/d-eSvNBlrSE

Here's what the other one is doing:
http://www.youtube.com/watch?v=XZkH8jANnHc&feature=plcp

Unfortunately, it's not a simple mechanical issue with the gears. It just sits there twitching even if I remove a gear:
http://www.youtube.com/watch?v=XZkH8jANnHc&feature=plcp

Any thoughts on what is going on here?

[Gregs///M]

Your last two videos seem to be the same. If the odo gear fails to move freely (will all other gears removed, unloaded) then something else is wrong.

Perhaps you are using the incorrect signal to drive the speed input?

[nando]

could be a component on the speedo PCB. the quality of the VDO board is pretty crummy - it's got a really awful 16v capacitor that's probably toast by now, and some other equally flaky components. you could try to rebuild the whole thing, would cost probably $5-$10 in components and your time to solder them.

the UAF 2115 chip that controls the speedo/odo is pretty robust/common, but everything else is crap (especially the PCB). could be a broken solder joint or trace, and even a cracked PCB wouldn't be a surprise.

this is the janky capacitor I speak of:


I replaced one with a modern 50v equivalent.

[nrubenstein]

Originally Posted by nando

could be a component on the speedo PCB. the quality of the VDO board is pretty crummy - it's got a really awful 16v capacitor that's probably toast by now, and some other equally flaky components. you could try to rebuild the whole thing, would cost probably $5-$10 in components and your time to solder them.

the UAF 2115 chip that controls the speedo/odo is pretty robust/common, but everything else is crap (especially the PCB). could be a broken solder joint or trace, and even a cracked PCB wouldn't be a surprise.

this is the janky capacitor I speak of:


I replaced one with a modern 50v equivalent.

Yeah, I've replaced the capacitor and resoldered the joints. I guess that I need to go over the solder traces.

[nrubenstein]

Originally Posted by Gregs///M

Your last two videos seem to be the same. If the odo gear fails to move freely (will all other gears removed, unloaded) then something else is wrong.

Perhaps you are using the incorrect signal to drive the speed input?

The signal is tested good on a Motometer and a VDO cluster, so I presume that it's fine.

Here is the correct link to the fully unloaded video:
http://www.youtube.com/watch?v=cUUyS...=ULd-eSvNBlrSE

[nrubenstein]

After swapping circuit boards and getting irritated, I took a brute force approach. As it turns out, swapping the M3 needle and face plate onto a Motometer speedo and then recalibrating it is a hell of a lot easier than worrying about this VDO shit.