Meade ETX 90

[Mikel56]

Hello,

I recently bought a relatively unused ETX 90 with the Autostar handset. My experience is limited to manual alt az but I’m learning. Reason I bought the ETX was to gain experience in tracking and goto.

After a gentle clean the optics proved good, nearly as good as my Swift 831 ! The telescope tracks very well although that was using the moon as a test. 
 

The issue I have is the goto. I have read and used the tips in Weasner’s excellent online guide. I have trained the telescope, learned about orientation and calibrated the motors. 

The alignment procedure I have followed and with a slight manual adjustment synchronised to the target. When I select another star or planet for observation the telescope travels to the necessary position however when I ask the telescope to return to the original aligned star as a test there’s a problem.  The altitude is spot on however the azimuth is out. I then ask the telescope to return to the previously observed star or planet but overshoots. The difference is about ten to fifteen degrees. When I go back and forward between the two observation points another ten to fifteen degrees is added each time. The altitude has no problems. It’s as if the goto has ten to 15 degrees error which is added at each repeat change. Ten to fifteen becomes twenty to thirty and so on.

It’s a bit frustrating but the tracking is good. Is there a simple solution ?

M

 

[NGC 1502]

I don’t use go-to, but as no one else has replied-

Are the batteries up to the job?  Fresh good quality batteries, correctly installed with clean contact points? Have you entered the date and time correctly having regard to the difference between the USA and UK method?  Have you used BST rather than GMT?

If the above doesn’t sort it I’m stumped, perhaps try posting again and hope someone helpful replies…..

[Carbon Brush]

Power may be the answer. Back in the days of ETX (20 years ago?) the general advice was to forget about AA cells and use a 12V external supply.
Or maybe that was retailers trying to boost powerbank sales?🤔 No seriously - slewing on AA cells was a known problem.
After many years the battery contacts will be tarnished and your 12V worth of alkalines may well be losing a bit to the multiple contacts.

When entering the time/date don't forget it is USA format. Mixing up month and day.
Also confusing information for GMT/BST - daylight saving!

Are you certain that you don't have clutch slip on the axes?

If you set it up on the wedge (polar mount) that may change the fault characteristic and give you a hint.

Sorry I can't be more specific. After many years of my ETX90 gathering dust I sold it a couple of years ago so am relying on memory.

Keep asking the questions.

David.
 

[michael8554]

There's no US format to the date, it's entered as eg 13 july 2024, no confusion.

The GoTo overshoots may be due to grease ln the encoder wheel causing miscount of the distancd travelled.

Michael 

[Mikel56]

Last night the only star I could see and name was Arcturus. I had the star in the centre and began to track. With a 10mm lens Arcturus stayed centre for towards half an hour. I was impressed ! From the hand controller data base I selected Izak and a star appeared dead centre. Going by Stellarium that indeed was correct for position. I then went back to Arcturus and with fingers crossed the altitude moved upwards, so far so good. However the movement kept rotating until about 180 degrees out ie bedroom window.

I’m using 8x1.5v rechargeable batteries in a separate unit plugged in to the external power supply. I check the voltage beforehand. I’ll recheck the times and dates but I think ok. There may be something about grease in the encoder wheel. I saw a video about that.

I think I may have to defork the Meade and buy an AZ Gtix, the one for two telescopes. 
 

Thanks for taking time to reply. If I have success with the Meade I’ll be in touch,

Regards,

M

[NGC 1502]

Deforking the optical tube would be my option, even if the go-to was ok.

The ETX 90 has good optics, the mount was a plastic toy in comparison…

[symmetal]

Are your rechargeable batteries actually 1.5V, like Lithium or Li-ion ones. Older NiMH or NiCad rechargeables are only 1.2V per cell and 8 cells only give 9.6V total. It's also worth measuring the battery voltage while the scope is slewing to check it's not dropping significantly.

Just a thought, but did you select and perform the 'train drives' routine using the handset after performing a 'calibrate motors'. This works out the backlash in each axis by asking you to centre a chosen object, like a distant aerial or lamppost for example, during the day. When doing the 'train drives' and you accidently overshoot centreing the object you're training on, don't reverse direction to centre it, as this will mess up the backlash calculations. Just start the train drives routine again from the beginning.

If you haven't done a train drives or performed a factory reset, it will have the backlash figures stored from the previous owner which could be way out. Unlikely to have 15 deg of backlash available to be stored but you never know. 😉

Alan

[Mikel56]

Hello,

 I checked the voltage of recharged batteries at 11.50v. Voltage at slewing is 11.23v and 11.3v whilst tracking. I think that should be ok. (I don’t use the integral battery holder as I connect with a separate unit to the power supply fitting).

I’ve done all the calibrations, training and so on and double checked times and dates etc. There may be an internal issue so next step will be the hammer and shifter !
 

The tracking is excellent and the optics very good, particularly for the moon which I enjoy.

Thanks again,

M

Edited July 17 by Mikel56

[Albir phil]

13 hours ago, Mikel56 said:

Last night the only star I could see and name was Arcturus. I had the star in the centre and began to track. With a 10mm lens Arcturus stayed centre for towards half an hour. I was impressed ! From the hand controller data base I selected Izak and a star appeared dead centre. Going by Stellarium that indeed was correct for position. I then went back to Arcturus and with fingers crossed the altitude moved upwards, so far so good. However the movement kept rotating until about 180 degrees out ie bedroom window.

I’m using 8x1.5v rechargeable batteries in a separate unit plugged in to the external power supply. I check the voltage beforehand. I’ll recheck the times and dates but I think ok. There may be something about grease in the encoder wheel. I saw a video about that.

I think I may have to defork the Meade and buy an AZ Gtix, the one for two telescopes. 
 

Thanks for taking time to reply. If I have success with the Meade I’ll be in touch,

Regards,

M

The  USA format is month then day then year My Mead LX90 did a similar thing untill I realized it had to be USA format 

[Mikel56]

Thanks Phil,

My screen is as attached. I can single star align no problem and check against Stellarium. After that the azimuth gets confused but the altitude is correct at any star selection thereafter. I think I need to have a look inside !
 

Regards,

M

[Albir phil]

2 hours ago, Mikel56 said:

Thanks Phil,

My screen is as attached. I can single star align no problem and check against Stellarium. After that the azimuth gets confused but the altitude is correct at any star selection thereafter. I think I need to have a look inside !
 

Regards,

M

Hi looking at your hand controller you have the day first, it should read July -7-2024 this is the way I set my LX 90 or it's all over the place