[The_bluester (Paul)]

I ran in to an issue last night with the Celestron focus motor on my SCT which I have resolved, but I thought I would post it here in case it is useful for someone else later.

I was running into issues with inconsistent operation, I had put it down to driver issues initially as it would work sometimes and then exhibit some odd behaviour, like not responding then suddenly moving quickly to the requested position. Last night it just stopped moving at all.

I removed it from the scope (which was difficult as the machine screw to release it from the focuser shaft was in a tricky spot and it wouldn’t move) and discovered that the retaining nut which holds the shaft that actually couples to the SCT focus knob had come very loose. With the nut loose the shaft was moving out of its support bearing and the large diameter gear on that shaft was binding on the housing and stopping the motor from moving, a quick tweak up with a spanner and all is back to normal. The nut is a very thin alloy one, I think I will redo it shortly with a drop of low grade loktite or it is likely to happen again.