Serving a Vixen GPD2 mount

[hotspur (Chris)]

Anyone got any suggestions on where I can find some advice on pulling apart a Vixen GPD2 mount.

I had session on saturday night,and the darn Declination started playing up,and appeared to 'stick' The first couple of hours everything seemed ok,with 3 and 5 minute subs.Then it all went to poo. We did a drift alignment.

The mount is on a pier in observatory,it appeared all was well P.A'ed. But as the evening went on that dec still went bad.So ended up turning it of and just used R.A all the 3 minute subs were all very passable and usable though.

But there is an issue,so we need to strip it down,and give its insides a good clean,and tune and grease (any recommendations).

Being in an observatory,maybe dust has got in,or some rust inside it.

Thanks for any thoughts or help.

[LewisM]

Dec:

Remove motor. Remove worm cover by loosening the 2 cap bolts - NOT the central one, as this is merely a tensioner. With the worm and carrier out of the way, remove the 2 cap bolts in the head dovetail slot. The dec puck will now come out. Regrease, clean, whatever. Also, the worm is brass, as tends to bend - I have a spare if need be (I have quite a few GPD2 spares sourced through Steve Massey or William Ng in HK).

RA:

Again, remove motor. Remove polar scope cover. Remove polar scope bezel. Loosen 3 SMALL set/grub screws that hold the scale onto it, and then remove the polar scope. Remove the small screw that locks the scale at the top (External silver one), and through it's hole, you can loosen off the RA ring grub screws etc. YOu can then loosen the RA ring, but will either need a proper bezel tool, make one, or a large set of split ring/circlip pliers. Back it off a touch - will loosen the RA sufficiently to balance RA well.

Pretty easy really - I once "hypertuned" my GPD2 in about 4 hours - including precise worm engagement (NO Dec backlash) and spur gear engagement (again, no backlash). I regreased the whole thing and SLIGHTLY lessened the tension on the RA shaft so it could be balanced accurately.

Dec BL is an issue with these, so they need to be adjusted fairly regularly - I do it every 6 months.