LX90 - Motor Unit Fault - discuss my options!!

[goldblade1983]

Oh dear, the subject says it all!

Was setting up my LX90 (8 inch, GPS UHTC) the other day and whilst it was aligning the power cable came slightly loose. I plugged it back in and then it basically stopped alignment procedure and came up with Motor Unit Fault.

Restarted the scope and no joy.  The handset will allow up and down so nothing wrong with the Dec side.  But 'left' will only work on 'max' speed and anything lower it seems to struggle.  'Right' is dead.  Therefore seems likely there is an issue with RA motor / chipset.

I called Steve Collingwood at SCTelescope and his initial thoughts were - reset the handset and if that doesn't work it's likely to be the motor control board.  I have reset the handset and that didn't work.  If it is the motor control board then it's £120 + postage both ways for a repair (and that's assuming that is what it is and nothing more expensive).

So here's the thing.  I have previously deforked this scope and used it on NEQ6 (unguided).  I had originally planned to do more astrophotography with it but quickly got frustrated without it being guided and so re-forked it and bought a WO GT81 80mm refractor which I now have a guidescope etc. attached to.  I am more comfortable with the guiding process now.

The way I see it I have 3 options:

1) Get it repaired and fork out probably about £180 (including postage costs) for a scope that's been re-forked once (there was no noticeable issues with pointing accuracy after I had done this - albeit it did struggle to find north automatically).  This way I can run two scopes simultaneously - one for astrophotography and one for visual, although in the last 12 months I can recall doing this just once.

2) Defork it and use it on NEQ6 again.  In doing so I would commit to setting it up guided so that I can get some better results for astrophotography.  This has the disadvantage of having one scope only at a time for  just now and also that set up time for neq6 is longer if I was just wanting it for visual only.

3) Sell the OTA, damaged mount, handset and field tripod individually or together and buy something else for the NEQ6 (a newt?). 

(a 4th option would be to attempt to repair it myself but not convinced I have enough knowledge or confidence to attempt this).

Would be happy to hear anyone else's thoughts.  Also would be happy to hear about results people have had with a guided LX90 8 inch for astrophotography (i.e. what the quality I can expect from it).  From previous research not many people seem to use them for astrophotography because they are as standard on alt / az mounts - but I would like to think at least someone out there has had them guided on an equatorial mount!

Cheers

Brian

PS - one final point is that the powertank I am using is a Maplin 5 in 1 powerstation with air compressor.  See here: http://www.maplin.co.uk/p/5-in-1-power-station-with-air-compressor-a67hy

As far as I know the power isn't regulated - is there any chance that this caused the fault and if so could the same thing happen with the NEQ6? If so will probably get a regulated tank!

[Carina Lass]

Or mount your ota on the mount with your gt81 and use one for guiding and one for ap.

You can swap to either no problem.

see pic

[r3i]

I used to own an LX90 and like you, I de-forked it and put it onto an NEQ6, as I got more into imaging and made much more progress that way. If you see yourself spending most of your time doing imaging in the future then IMHO using a guided GEM will give you better results.

[goldblade1983]

Do you have any examples of your results with lx90 you are willing to share? :-)

[Paul M]

Oh dear, the subject says it all!

PS - one final point is that the powertank I am using is a Maplin 5 in 1 powerstation with air compressor.  See here: http://www.maplin.co.uk/p/5-in-1-power-station-with-air-compressor-a67hy

As far as I know the power isn't regulated - is there any chance that this caused the fault and if so could the same thing happen with the NEQ6? If so will probably get a regulated tank!

I don't know that any of the power tanks are actually voltage regulated.

My SkyWatcher one isn't to the best of my knowledge.

A healthy and fully charged battery will show between 12 and 13.5 volts off charge typically. That will drop only slightly under moderate load and decrease gradually as the battery discharges. So nothing much to regulate really. No regulating circuit would sustain 12v at the outlet terminals once the batteries charge dropped off anyway.

My power tank can't be used at the same time that it is charging so there is little risk of spikes from the charging causing issues.

I don't know about the maplin unit in the link but I would avoid using it while it is charging (if that is possible) as it isn't intended for supplying electronics and the charging circuit might be quite "rough" i.e. full of ripple.

[Astroboffin]

Hi,

I own an LX90 and use it on a wedge, and get 15minute subs with nice round stars, so this kit will,guide very nicely, but the important thing is balance, if you get that right with a piggybacked guide scope then it will work finre, if you don't balance then forget it, in fact you will damage the mounts gears.

If you already have an NEQ6 mount, then put it on that, otherwise leave where it is and guide on a wedge.

As for the repair, then that is a difficult one, as it could be expensive, as you say.

My advice is based on the fact that these scope will guide very well, as long as certain rules are followed, and that means balance, balance and balance....all the way, this is the most important thing, and I can't stress it enough.

Regards

AB

[goldblade1983]

Thanks again any actual results from guided lx90 scope would be helpful. At moment I'm thinking of putting my 80mm apo on top and using neq6. Can then use either scope for guiding and shooting / vice versa. Only thing making me think that's a bad idea is that I don't have a permanent set up so I have to lug it all together which is fairly heavy. I have extension bar and 10kgs of counterweights. Think that's enough to take an lx90 with wo gt81 attached to back? !

[Astroboffin]

Thanks again any actual results from guided lx90 scope would be helpful. At moment I'm thinking of putting my 80mm apo on top and using neq6. Can then use either scope for guiding and shooting / vice versa. Only thing making me think that's a bad idea is that I don't have a permanent set up so I have to lug it all together which is fairly heavy. I have extension bar and 10kgs of counterweights. Think that's enough to take an lx90 with wo gt81 attached to back? !

I have a williams optics ZS66 piggybacked on my LX90 and it only requires 2.5kg of counter weight, so for your scope I would think 4kg was more than enough, but not sure of the weight of your 81mm scope, including camera or guide camera....

But it will be no where near 10kg..

Regards

AB

[schmeah]

I tried for some time to do guided imaging with an LX90 years ago, and could never get more than two or three minute long exposures. I think I had a lot of flexure due to inability to lock down the primary mirror. After moving to an LX200 I had no problems. AB, I'd love to see some of your some images. Fifteen minute subs would be remarkable with that set up.

Derek

[goldblade1983]

I heard 8 inch suffers less mirror flop compared to larger models?

[Astroboffin]

I have never really suffered with mirror flop, as I have a different focuser that what was supplied on the scope, (see avatar image left) the problem with the stock focuser is that there is a hole at the end of the threaded bar that is on the focuser, and this hole slots over a pin on the side of the primary mirror, to enable the focuser to push and pull the mirror up and down the baffle tube.

Because the hole is a bit bigger that the pin, the mirror when pointing up can slip slightly causing mirror flop.

On my focuser that hole is the same size, but there is a locking nut, so when fitted over the pin the locking nut is tightened to stop the movement.

Plus it has extra bearings fitted to give a smoother focus action.

Simple fix but it does work

Regards

AB

[Carina Lass]

Odd, my lx90 is bog standard and there isn't even any backlash never mind flop.

I can adjust my focus using x10 on APT and a batinov mask - which equates to 800x - without the image shifting more than a few pixels.