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Problem with Controller for old Meade Research Grade Mount

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#1 PaulEK

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Posted 28 August 2018 - 01:04 PM

I recently acquired a Meade Research Grade mount, from the 1980s, I believe. It has an issue, and I posted about it on the Classics forum, but got no suggestions, so I'm trying here.

 

The mount itself functions fine. It's meant to use 115vac wall current, and you can simply plug it in to get RA tracking. That works. But it also came with a control box and hand controller. When working properly, this controller provides motor control in both RA and via a small motor on a tangent arm for Dec adjustment. This is really helpful, since the huge mount does not have manual slow motion controls.

 

Unfortunately, the controller is not working properly. The Dec control works fine, but RA does not work at all with the control box. Since RA does track when plugged directly into the wall, this means that the issue must be with the controller box and hand controller. My son, who is pretty knowledgeable about electronics, and he opened the box and hand controller up. Because we don't have a schematic of the guts of these things, and because they are more complex than we anticipated, we are unable to even test them accurately, let alone fix them.

 

My son did find two things: First, he found that there is voltage going to the RA connection, and it's 50vac. We don't know if that's proper or not. Second, inside the controller, he found a loose wire. The thing is, the wire is quite short, and we cannot find a place that it will reach that seems like it is where the loose end should attach.

 

So, I'm hoping someone that has one of these controllers, or has had one in the past, might be able to help us. It would be great if someone could open up their working hand controller and compare it to the photo below, and then let us know where the wire attaches. Or maybe someone has the schematic. Or maybe it's a known problem with these that has nothing to do with the loose wire. We'd like to get the mount up and running, after a tune-up and retouching of the paint, so that we can sell it -- along with an 8-inch f/8 reflector -- in order to raise funds to support our public observatory. We have more scopes than we can use already, and would like other things, like an h-alpha solar attachment for one of our refractors.

 

Here's the mount (you can just see the reflector behind it, which has a cell and mirror made by Edmunds):

 

gem1 sm.jpg



#2 PaulEK

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Posted 28 August 2018 - 01:05 PM

Here's the controller box and hand controller:

 

gem3 sm.jpg



#3 PaulEK

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Posted 28 August 2018 - 01:06 PM

Here's the guts of the controller box:

 

gem4 sm.jpg



#4 PaulEK

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Posted 28 August 2018 - 01:15 PM

And, finally, here are the innards of the hand controller, with an arrow pointing at the short, loose wire:

 

gem 6.jpg

 

Any pointers or help will be gratefully appreciated!



#5 photoracer18

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Posted 28 August 2018 - 02:12 PM

Here is how its supposed to work. When the switch is in the AC position the gray AC cable has to be plugged into an AC power source. Then the clock drive AC input is plugged into the black AC connector on the box and the DC power for the DEC drive is plugged into the DEC port and the circuitry has a transformer to produce 12v DC for that drive all controlled by the joystick. Assuming the AC drive still has its original AC synchronous motor then the joystick will control that by varying the AC frequency.

 

In the field you switch to the DC position and plug a connector from a fully chanrged external DC battery (like a car battery) into the port labeled Battery. Then the box converts DC into AC for the RA drive and uses its own power to make 12v for the DEC. This is the same basic way Meade, Celestron, Digitrak and Accutrack drive controllers work, although some like the Digitrak were available in models that had the DC field battery built into the big case with an external charger port to charge the battery (Digitrak II). I can't tell from the pictures if anything is wrong. I never had the chance to work on a Meade and I don't have a test rig to test it with either. Also I don't know if anyone has a set of Meade schematics.


Edited by photoracer18, 28 August 2018 - 02:13 PM.


#6 J A VOLK

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Posted 28 August 2018 - 02:23 PM

Note that the RA control would be very minimal, maybe only a few percent. You would hardly notice without using a reticle eyepiece. You should be able to hear the frequency change if you listen carefully when commanding RA. The dec moves much faster relative to RA, possible it is actually moving - check this first. That being said I don't think there should be a loose wire, can you see with a loupe where there is solder that is lacking a wire? It could be extraneous?

#7 PaulEK

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Posted 28 August 2018 - 02:41 PM

Thanks for the suggestions!

 

photoracer18: I'm pretty sure we set things up and tested them in the way you describe, but I'll try again. We got nothing from the RA motor at all with the controller hooked up.

 

I may have access to an Accu-track 4000. I did not know which mounts it was meant for. It seems you are saying that it should work with this mount; is that correct? That would solve our problem! But, of course, we'll need to test it, too. These things have been in storage for years.

 

J A VOLK: Thanks for the point about how little the RA control would change things. Still, it might be enough for a visual observer who did not polar align precisely. Unlike so many other mounts, there are no manual slow motion controls, as I wrote in my OP. Anything would be a help.




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