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Move commands do not work on my classic LX200

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#1 rimcrazy

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Posted 02 February 2013 - 11:29 AM

I will try to make this short and concise. I did the capacitor repair job on my LX200 about 2 weeks ago. Everything worked fine. I tested it actually one at a time after every fix to be sure that fixed was performed correctly. As I said, all worked well. I've been adding things to my scope to prepare it for complete automated control. Last night I powered it up for the first time with my StarShooter guide camera connected, both USB to my computer and the ST4 port to the CCD port on the LX200. When I powered it up, not thinking it would be an issue, the StarShooter was already powered up and running and connected to the LX200. I turned on the LX200 and the RA and DEC motors both took off into the weeds. I quickly disengaged the clutches and then shut the LX200 off. I turned the LX200 on again, same thing. Ok so now I'm thinking I must have hosed something with my repairs. I pull the scope off, check it out and it appears to be fine. I made a couple of minor changes to be sure nothing was shorting out inside. Put it all back together and back on the mount. I checked this morning and find everything works with the exception of MOVE commands. Manual slew from the keypad does not work. If I pick an object and hit GoTo both RA and DEC motors engage and the telescope slews to the object. Hit N,S,E,W buttons and nothing regardless of the 4 selectable move rates. I hooked up TheSkyX to the telescope. If I pick and object and hit slew, the telescope will slew to the object. If I am on the Jog tab I can jog U,D,L,R. If I go to the Move tab and select any movement none of these work.

I'm thinking there must be something unique in the hardware on one of the boards that specifically controls move commands. That is the only thing that makes sense for both the Keypad and TheSkyX to fail to execute a move.

Any assistance would be greatly appreciated. This is very strange indeed.
(Posting here and the LX200 Classic Forum to cover my bases)

#2 rimcrazy

rimcrazy

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Posted 02 February 2013 - 12:52 PM

As an FYI to anyone else who may have this issue I found out from another board that when a CCD camera is attached for tracking it overrides the move command, which is exactly how it is behaving. (I did not know this as this is the first I've used a tracking camera with my telescope) Pulled up the schematics and I see that there are +5V pullups on the N,S,E,W CCD inputs to the main board. Pulled out my trusty Fluke DVM, powered up the LX200 and checked the port with just the cable checking the levels at the other end. Low and behold, one of the pins appears to be shorted low so that must be my problem. I'll have to pull the board and find out what the issue is. I'll post an answer for future reference for someone else should they duplicate my errors.

#3 Christopher Erickson

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Posted 02 February 2013 - 04:59 PM

Excellent sleuthing!

#4 rimcrazy

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Posted 02 February 2013 - 06:13 PM

Excellent sleuthing!


Yea.... tracked it down to U11, a 74LS14. $0.67 from Digikey. The input is clearly shorted out. From the connector it's just a 4.7K pull up to +5 so it has to be in the IC. I am not sure exactly how it happened. I had my scope set up on the patio outside. There was some rain but I had everything covered very well. I'm guessing perhaps some water got into the connector. It was either dirty or residue created something wrong. Anyway the input got blown. Will verify when the parts arrive and I swap it out. I have a good soldering setup (Solder sucker, quality Weller iron, etc.) so it should not be a huge chore to swap out. It's interesting, I don't have an O-Scope (wish I did) but in ringing things out, I had my original Meade 18V (really about 22V) brick applied and I was appalled at the +5 internal supply. Just on my Fluke I could see it was oscillating between 3.9 and 4.9 so it has to have a terrible oscillation on it. I'd purchased a new, nice and clean, 15Vdc supply and with that hooked up +5 was nice, clean and stable. (At least as far as I can tell with just a DVM). Holy *BLEEP* those Meade bricks have to be the biggest POS power supply's I've ever seen. I'd heard they were bad but good grief. No wonder the regulator in there was heating like an oven. Hopefully nothing else went. As I said I can command things to work so I'm guessing the rest should be fine. I will have to check the pullup when I pull the ic out to be sure that leg of the ladder has not been blown too. If so I'll have to get a replacement for that too.






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