Skywatcher AZ Goto mount motor seized - advice needed!

[DavB]

Hello,

I'm fairly new to this so please bear with me...

I have a Skywatcher AZ Goto telescope - it has been stored inside and hasn't been used for probably two years or so.  My grandson is now getting interested in the night sky so I got it out but found that the ALT slew wasn't working - no movement at all.

I've dismantled the mount as per a very good video I found on the web hoping that it would be a simple case of cleaning and re-greasing - but sadly not. 

I have removed the main large cog wheel assembly and verified that the motor itself is stuck.  When I use the slew buttons on the handset there is a slight click from the motor but no discernable rotation opf the small cog wheel.  I have removed the motor completely from the mount and cannot turn the small cog by hand (don't know if this is expected though?).

What next?  Should I attempt to disassemble the motor to get to the internal gear assembly?  THe video suggests that this is not an easy task but I don't see where else to go. 

 

All suggestions very much welcome!

 

 

 

 

[Albir phil]

If you're hearing a click it looks like it's stuck as it seems to be attempting to move.i personally would Open it up to see what's going on,take pictures as you take it apart at each stage.Good luck hope you can sort it 🤔

[MikeAa]

Hmmm. Are you able to swap the motor for the AZ one and check if the fault follows the motor? Reason for saying is that I am wondering if the drive electronics is working correctly.  I think this is a stepper motor, so it needs drive to a pair of coils to make it rotate. The motor is unlikely to seize if it's been stored inside. 

[PhilB61]

It shouldn't turn by hand, it's an extremely high reduction ratio and attempting to do so risks stripping the tiny plastic gears inside, only the last few reduction gears are metal. To see any discernable movement when powered you need to select the highest slew speed first. Also it's a good idea to try swapping the two motors over, to isolate if it is the motor/gearbox or the control board. These are relatively simple DC motors not steppers, the opposite end from the gearbox is a step counter, take care not to damage the fine fingers or dislodge the optical sensor.

[PhilB61]

On the other hand the step counter fingers/ encoder wheel should be visible moving at any speed (although very slowly at tracking rate) you could very very gently try turning this by hand. There's nothing serviceable in the gearbox end, other than trying fresh grease but the grease in my 10 year old was still good and soft. Be aware if you do take apart as well as the tiny plastic gears, there are some much smaller shims which sit on some of the gear shafts, from recollection just 1-2mm in diameter and very thin. The motor/gearbox is only available as a complete unit if you need to replace it.

[DavB]

-Thanks for all the info.  I was about to switch the ALT and AZ motor connections but put them back in their correct sockets to check out a couple of other things first.  This is what I've found: =

- With slew rate set to 9 ALT doesn't work, AZ does.

- With slew rate set to 7 both ALT and AZ work (but AZ sounds like it's not that smooth).

- With slew rate set to 8 both ALT and AZ work internittently.

- At lower slew rates I can't detect any motion but that might be normal.

I tried  to align the  mount using the 2 object method.  With rate set to 7 both motors were turning OK.  After I had set the first object and selected the second the motors didn't turn at all, it just said the alignment was successful.

Any ideas what on earth could be going on??

[Cosmic Geoff]

34 minutes ago, DavB said:

Any ideas what on earth could be going on??

A power supply problem? Try fitting a proper +12v regulated power supply or power pack.  If you are using 2 year old internal AA batteries I'm not surprised it doesn't work. 

[PhilB61]

So it appears both motors/drivers are working, just not as expected. Agree with the above poster, before anymore disassembly etc check that you have a good power supply, inadequate power can cause all sorts of strange behaviour.

[DavB]

Thank you very much Cosmic Geoff and PhilB61.  The power supply was indeed the problem!

When I bought the scope from an eBay seller it came with a portable car battery jump starter.  To use the scope I charge this overnight and then use it to power the scope.  I was taking a shortcut this time by plugging the charger used to power up the jump starter directly into the scope.  Although this appeared to work (handset responded as expected) I guess the voltage wasn't up to driving the motors properly.  Setting things up using the jump starter everything works as expected.  I feel a bit stupid now, but very pleased that I didn't disassemble the motor gearbox.

One final thing, what degreaser and grease would you recommend that I use in order to clean and re-grease the ALT gears seeing that I wiped off a lot of the old grease.  Can I just use a bog standard Kilrock degreaser that doubles up for cleaning ovens or WD-40 based product or should it be a specialist product?  For grease I believe I need a white lithium based grease?

Thanks in advance and for all the useful pointers given by everyone.  Much appreciated!

 

DavidB

[MikeAa]

Glad you solved it! I wouldn't have considered the power supply give that the other motor was working correctly. Something else I learned today!! 😀

[PhilB61]

Thanks for updating and glad that things are working properly now. That wall charger looks like a trickle type so very low current output which is probably fortunate as it's almost certainly too high a voltage (a 12v power pack is usually charged at around 15v). Regards degreasing any mild degreaser but nothing too aggressive like oven cleaner, and make sure it doesn't get onto electronic boards etc. I've used methylated spirits or surgical spirits and a toothbrush for cleaning off grease. Regarding new grease Super lube seems to be highly regarded, myself I've tended to use whatever I have available at the time, my old eq1/2 mount I used grease that you might use in car wheel bearings! More recently with Skywatcher and ioptron mounts I've used a teflon enhanced grease typically used on modern bicycle. I'm sure others have their preferred brands.