LX200 GPS runaway motors when started up.

[Inmykombi (Geoff)]

I am hoping someone has a cure for this issue I have with my LX200GPS mount.
When I power it up, a random running of both the ALT and AZ motors occurs. Sometimes slow, sometimes fast, sometimes one at a time, other times both together.
And sometimes not at all.
The display in the hand controller says " motor stalled" but this is not the case as the motors run until they hit their stop point, unless I release the clutch and then they just keep going until turned off.
I have removed the main PCB and there appears to be no blown or damaged parts. I even cleaned the PCB with special PCB cleaner. This didnt help.
I changed the small button battery in the mount as well, but this did not help either.

Does anyone have any advice for me if they have had the same thing happen totheir LX200 GPS.
I would love to know what's wrong, but I just don't know where to start.

Any help greatly appreciated.

geoffro.

[beren]

Yes happened to me when I had one, had to replace the motor board. It's a easy swap out, try one of the larger Meade retailers for stock.....

https://telescopes.net/store/meade-l...ver-board.html

[Inmykombi (Geoff)]

Thx for the reply Beren. Is that for just the dec motor ? Or does it do both the motors.?

[Atmos (Colin)]

I remember mine doing the same thing at one stage and it ended up being because a “Smart Drive” setting something to that effect was turned on on the handset.

[redbeard (Damien)]

Hi Geoff,

2 other things to check before swapping circuit boards:

1. Sometimes the hand controller buttons can cause runaway as they have rubber conductive pads that press onto a circuit track for contact. At times the rubber wears off and can make the button not work at all or it can leave deposits on the circuit track that makes a contact and then the motors can move. Take the hand controller apart and have a look. I have had this happen on a similar scope. The older the handbox the worse it will be, with use of course. I had to buy a new handbox for my LX200GPS as the one it came with was unusable due to the above.

2. Upload the latest firmware. 4.2G

Simple things to check and good luck.

Cheers,

Damien.

[AndrewJ]

Gday Geoff

The display in the hand controller says " motor stalled" but this is not the case as the motors run until they hit their stop point,

The main board tells the motor cards to move the motor and then has to continually ask the motor cards for position info.
If the main card asks for position data and doesnt receive it back, it declares that fault.
If the motor card is asked to move, it will ( automatically ) keep upping the power until it gets to speed. If the encoder feedback loop isnt working, the speed just keeps going up, but the "recorded" movement will be zero.
Random starting and stopping of both motors is odd and really sounds like the main card has problems, not the motor cards, but it may just be grot/corrosion in the push on connectors.
You could try removing the covers and refitting all the push on connectors several times ( to wipe the connectors clean )
In many cases this fixes the problem.

Andrew

[Inmykombi (Geoff)]

Originally Posted by Atmos

I remember mine doing the same thing at one stage and it ended up being because a “Smart Drive” setting something to that effect was turned on on the handset.

Thx Atmos, I will check the settings.

[Inmykombi (Geoff)]

Originally Posted by redbeard

Hi Geoff,

2 other things to check before swapping circuit boards:

1. Sometimes the hand controller buttons can cause runaway as they have rubber conductive pads that press onto a circuit track for contact. At times the rubber wears off and can make the button not work at all or it can leave deposits on the circuit track that makes a contact and then the motors can move. Take the hand controller apart and have a look. I have had this happen on a similar scope. The older the handbox the worse it will be, with use of course. I had to buy a new handbox for my LX200GPS as the one it came with was unusable due to the above.

2. Upload the latest firmware. 4.2G

Simple things to check and good luck.

Cheers,

Damien.

Thx Damien, I’ll check the hand box first. But I also can’t seem to connect my scope to my laptop. I can’t find the correct combination of settings to allow th scope to “connect “ . It already has 4.2 G as well. Cheers .

[Inmykombi (Geoff)]

Originally Posted by AndrewJ

Gday Geoff

The main board tells the motor cards to move the motor and then has to continually ask the motor cards for position info.
If the main card asks for position data and doesnt receive it back, it declares that fault.
If the motor card is asked to move, it will ( automatically ) keep upping the power until it gets to speed. If the encoder feedback loop isnt working, the speed just keeps going up, but the "recorded" movement will be zero.
Random starting and stopping of both motors is odd and really sounds like the main card has problems, not the motor cards, but it may just be grot/corrosion in the push on connectors.
You could try removing the covers and refitting all the push on connectors several times ( to wipe the connectors clean )
In many cases this fixes the problem.

Andrew

Thx Andrew, all the connectors are clean and dry. I made sure they were after I used some PCB cleaner on them. It does sound like the Main PCB then, if this is the one that control the motors and movement or encoder inputs.
I appreciate your help. Cheers.

[AndrewJ]

Gday Geoff
The main PCB is the front panel ( ie the expensive one )
It merely sends simple commands to the motor cards
and the motor cards do the rest.
The normal cause of single axis repeatable runaways is encoder problems
but if both axes fail and in an erratic manner, its normally the main board.
It may also be damaged firmware, but the fact you cant connect to the scope is also a concern as i would suggest reloading the firmware first.
As to connecting, there are several apps out there that will try to find a Meade scope using automated processes.
My PEC editor will try,
http://members.optusnet.com.au/johansea/
StarPatch will try,
http://www.stargps.ca/downloads.htm
Meades ASU will try.
All you do with my app is connect the serial cable to the mount and start the mount.
Start my app and let it try to autodetect,
It will try all available ports at all possible bauds to see if a Meade scope is connected.
If you can connect, i suggest using StarPatch
to reload the firmware as a next step

There is also an internal diagnostic routine you can run
that will bypass the normal firmware but i need to pm that
as the instructions are a bit long winded.

Andrew