Can anyone help? Broken Skymax 90

[Tonys]

I'm struggling to fix my Skymax 90, which I use for viewing the moon. Last time out it wouldn't come to focus on anything and I quickly realised that the focusing knob wasn't turning as many times as it should do lock to lock. I have now dismantled it completely (thanks to Yeti Monster's earlier posts), cleaned and relubed and reassembled but to no avail. The focuser screws in and out all the way when the mirror/focuser assembly is outside the tube but travel is very much limited when I put it back in. I also noticed that at the end of focus knob travel in the clockwise direction the image (viewing without an eyepiece) shifts alarmingly, which I think is saying that the mirror is somehow tilting. The scope wasn't expensive, but I think it performs well optically and now that I've had the courage to take it apart I'd be well pleased if I can get it working again. Any advice would be appreciated.

[JamesF]

Has the mirror become loose on the carriage, or the plate that connects the focuser rod to the mirror carriage become lose at the carriage end?

James

[JamesF]

Or, come to think of it, is the baffle tube perhaps loose where it passes through the backplate of the OTA?

James

[Tonys]

Thanks James. This morning I tackled it again and found that the connection between the focuser screw/rod and the mirror backplate was a little loose, as you suggested. In the end I reassembled everything outside of the scope tube, adjusting the rod position to ensure free focus knob travel when everything was fastened. Then, rather than disassembling again to fit the mirror through the front of the scope tube I just screwed the whole assembly into the back of the tube. Works great now, except I need to find a new tube o-ring as it broke. Thanks again.

[JamesF]

Excellent news

I'm not sure my 127 Mak has an O-ring.  In fact I'm sure it doesn't.  It was just a long length of circular section rubber/whatever.  If course that doesn't mean it wasn't broken by an earlier owner, but it didn't look that way when I took the scope apart.

James

[101nut]

If it's a clean break, a tiny drop of super glue is the stuff for joining the o-ring ...

AndyG

[Tonys]

I suspect the two ends were never joined up as you say. Thanks for the super glue tip idea Andy - sounds the way to do it. I can't think why this seal is needed though.

[happy-kat]

Supergue weeps chemicals into the air and can melt some materials. I would not use superglue in a contained space as it might cause fogging in the tube.

[happy-kat]

Linky

http://stargazerslounge.com/topic/198992-thoughts-on-sticking-a-lens/?fromsearch=1

[JamesF]

I can't think why this seal is needed though.

I suspect it is a mechanical seal to take up any slack allowed by the threads of the collimation bolts and thus prevent the backplate moving.

James

[Tonys]

Maybe not the superglue then ! I think I'll try a little grease around the circumference to hold it in place while I fit the backplate to the tube. Cheers

[JamesF]

Unfortunately I can't recall how I put mine back together whilst keeping it in place

Once reassembled you will need to make sure the baffle tube is square and collimate the scope.  Collimation is a bit more of a faff and more time-consuming than with a newt, but as you've had enough patience to take the scope apart and reassemble it I'm sure you'll be ok

James

[Tonys]

Hopefully job complete! I managed to keep the rubber strip in place and daylight collimation looks okay using the collimator. The focusing action is really smooth now. Thanks all for your help.

[JamesF]

Pleased to hear it's all back together and working

James