Mount not behaving as it should and I'm at a loss

[Brent]

Firstly, apologies for the long post, I just wanted to give as much detail as possible.

My mount is an LXD75 which I've been guiding for about 8 months. I use Alignmaster for PA very successfully and achieve fairly flat PHD dec graphs and (usually!) decent RA as well.

However, Thursday last week I spent 5 hours fighting with the guiding, re-doing the PA four times until I eventually gave up - both RA & Dec were all over and I couldn't make sense of it.

When I got the mount back in the garage I had a look and noticed a loose bolt in the casing which was allowing a degree or so of movement around the RA with the clutch on (Picture below with loose bolt arrowed).

I put the casing back in position & tightened the bolt up hoping that I had found the culprit.

Last night I set up, did my usual PA with Alignmaster (handbox working well), checked slewing on different speeds (everything was fine, motors sounded normal) and then started PHD up.

Here is where the problem is: during calibration the mount now barely moves the star to the west (the left edge of the green box will move slowly to within a couple of pixels of the yellow north/south line but will then pretty much stay there until 63 steps are reached and it fails). I'm not sure about east, north and south as it always fails on west.

I've changed the calibration step from 1500 (which would finish calibration in about 17 steps in both Dec & RA before) up to 2000, 2500 and I even tried 6000, all with no effect.

I don't understand how the mount can behave properly when slewing and hit every target, but fail at calibration.

I've also looked in the inspection panels of the motor housings and the gears appear to be meshed properly.

Any ideas? I'm loathe to strip it down, unless necessary, as I'm good at taking things apart and them never working properly again.

I'm at a loss now and I fear this will be the end of a very enjoyable AP adventure if I can't fix it, because I can't afford a new mount.

[m.tweedy]

When I had my lxd55 I joined this grouphttp://www.weasner.com/lxd/

It is a goldmine of specialised information for your mount.

[Brent]

Thanks for the link, I've been there before but will take another look for these specfics.

As regards my issue, after some pretty extensive testing I think I may have found the problem but need a decent night to try it properly - Monday looks promising.

I'll update the thread once I know for certain, for the benefit of anyone coming to it from search in the future.