I'm not quite sure how the electronics decides what the UC should do, but it does seem to me that rather than following directly the up or down order from the Tx/Rx it takes its orders from a bip-stable circuit of some kind. that can only be triggered into telling it to go UP when it is in the DOWN position - and vice versa.

This seems to be why neither UC will reverse direction part-way, and once it has been triggered to move by something, in error, it has to complete the cycle rather than suffering a brief g;itch out of position.

I see this as a further problem, if near the ground, because of the time a complete cycle can take. In other words what would otherwise be a brief glitch away from the DOWN position in preparation for landing, becomes 2 or 3 seconds not locked up or down. I suspect that any touch-down when not in the locked position, imposing side loads on the leg, would do the leadsrew no good at all.

In your particular case my guess is that something is triggering the bistable circuit in that unit to the DOWN position. As I have commented here, even just touching a screwdriver lightly on the frame could be enough to trigger that one, or just as likely the other one, into cycling. I would be tempted to look for metal-to-metal noise in the offending unit or nearby. and to try eliminating it by attaching short flexible leads to any parts that might be rattliing. Or the frames to battery negative perhaps.

Others have confirmed my findings of "high spots" in the movement where the precise nature of the rubbing parfts at that point in the travel causes the current draw to rise above normal, and as we know that can trip the current overload circuit. I would therefore also look for tight spots in the moving parts, as reported here and on the other web sites I identified above, e.g. the sharp corner between locking slot and transition slot, or inadequte sideways clearance (easily checked by slackening the locking screws to see if the movement frees up. My view is that if having the screws properly tight tends to make the movement jam, the right answer is NOT to fly with the screws slack, but to fit whatever thin shims are needed between the spacers and the frames to provide proper clearance with the screws tight.

Incidentally, the photos of my servo adaptation are now in place on my web site.




But as I say, I am only guessing.