Skywatcher GoTo AltAz Bearing adjustment

[tjc55555]

Hi there, looking for help on how to adjust the altitude bearing stiffness on a Skywatcher 250XP GoTo SynScan Alt Az. Currently the scope is too top heavy and it sinks on its own at low altitude. Any advice welcome :-)

[Geoff Lister]

Hello, and welcome to SGL.

I have the same 'scope, and had similar problems, particularly when using a 2" eyepiece or my 1.25" binoviewer and  a pair of eyepieces.

The mount axis friction is a compromise between manual and motor movement, and I am sure that the initial friction on the clutch was too low. It is adjusted by tightening the Nyloc nut on the altitude drive shaft. Unfortunately, this nut is covered when the optical tube is in place; so it is a case of removing the optical tube, tightening the nut a few degrees, replacing the optical tube, and doing some manual and handset-controlled movements; repeating this sequence until you have reached a satisfactory compromise. From memory, I used a 13mm socket spanner, and tighened the nut about a quarter of a turn.

I also checked the balance of the optical tube, using a piece of 40mm dishwasher waste pipe as the fulcrum. It was definately front-heavy, even with a lightweight 1.25" eyepiece. I ended up adding a weight at the primary mirror end of the main tube. This photo shows the weight that I needed to balance a x2 Barlow + Binoviewer + eyepiece + webcam. I think it was about 1kg.

I hope this helps.

Geoff