Please help

[Pitch Black Skies]

Where can I find a replacement LXD-75 RA motor assembly?

 

 

[NGC 1502]

Try ENS Optical Birmingham.  An email may turn up something not shown in their online listings.

Hope you sort it, Ed.

[Dr_Ju_ju]

Maybe a silly question, but what is actually wrong with the one you have ??   it may be easier to repair your existing unit...

[Pitch Black Skies]

2 hours ago, Dr_Ju_ju said:

Maybe a silly question, but what is actually wrong with the one you have ??   it may be easier to repair your existing unit...

Not a silly question. 2 wires have broken. I'm bringing it to an electronic repair person tomorrow.

[Dr_Ju_ju]

Yep, putting my electronics engineering hat on, that is a simple repair.....

[Pitch Black Skies]

I damaged the plug trying to fix it myself. I got a quote of €50 to have it repaired.

[Dr_Ju_ju]

If you were only closer, but hey ho,  I suppose €50 is reasonable.... 

[Pitch Black Skies]

Sound, I think it is too to be honest. Just hate spending money 😔😂

[Pitch Black Skies]

So just a bit of an update guys.

I've had the wires re-soldered.

The go-to is still slewing the telescope to a completely incorrect part of the sky, and then just stops and displays a motor unit fault on the hand controller.

Very disappointing.

[malc-c]

Not had a lot to do with Mead, but when a Skywatcher handset reports "no response" to either a single or both axis it normally means the main processors have been damaged, often by plugging the wrong cable into the wrong port.

Googling your issue it would seem based on old discussions of people experiencing the same issues that the same logic would apply and the problem is in the communications between the handset and the processor(s) on the motor board.  Now I presume you have tried all the usual stuff of checking connections, cleaning contacts and making sure the mount is powered by a suitable supply ?  If so then it could be the main motor board that has developed a fault.  Most mounts have a process where the handset sends out a "hello, what mount are you and where you are pointing" message, and expects the mount to respond with "I'm a XXX mount and here's my current position".  If it fails to receive that response it then halts its set up procedure and reports a problem.

The exact cause for the motor board to report the error isn't clear and you may need to dismantle the mount to check for things that may be obvious.  I don't think its an encoder or motor issue as apparently if one motor or its driver had failed, or the encoder wasn't readable the error message is different.

Here is an old post where the user incorrectly connected the wrong handset (het had two Mead scopes) - but it's not conclusive if the issue was ever resolved through reflashing the firmware.

In this post the problem was a broken wire....

Rather than fill up the thread with links to old forum posts, just google " LXD 75 motor unit fault " and see how you get on.   In the past I've repaired around 8 Skywatcher motor boards by replacing the damaged processors with new ones programmed with the SW firmware.  I'm not sure if that would be an option with the Mead as the firmware needs to be processed first and the Mead firmware may not allow that processing to happen.  They do however seem to use a 16C268 Pic micros which are a one time program device, so a more modern flash alternative would be needed if the firmware could be cracked.

[malc-c]

To be honest I would have replaced the connector on the board and  re-terminated the cables - If you paid 50 euros for a "professional" repair I think its fair, but it's not a professional job to cut off the connector and solder the wires direct.

I've replied to your new thread - It might be worth locking this thread so as not to duplicate posts ...

Edit - I've requested the moderators to merge your two threads as both are relevant and here we can follow the issues you've had and what's been done to fix it

Edited September 16, 2021 by malc-c
update

[michael8554]

https://www.cloudynights.com/topic/608291-etx-motor-unit-fault/

michael

[pete_l]

3 hours ago, malc-c said:

To be honest I would have replaced the connector on the board and  re-terminated the cables

Yes, provided a replacement connector was available - or the old one salvageable. It's generally considered bad practice to solder wires directly onto a PCB - no strain relief, for one thing.
One probably daft suggestion; have the wires been soldered to the correct positions? In the first photo we can only see some of them

Maybe a cracked track from when the OP tried to remove the plug? Or the underlying reason why PBS wanted to remove it in the first place.

Edited September 16, 2021 by pete_l

[malc-c]

Pete, if replaced as a set (ie both the part that gets soldered to the PCB and the mating part that has the cables) then it wouldn't be an issue.  Most connectors are made to one of two or three  standard pitch types so it's easy enough to source something that fits.

I agree that something is strange as normally if its a communication issue you wouldn't get the situation where the mount starts to move but then stops and reports an error.  This could be more related to motor control such as FET that is in the process of braking down and when current flows gets hot and fails ??

[malc-c]

Found another thread of similar nature  here  

The fault was in the cabling 

Quote

Thank you all! I've just solved it.

I changed the plug head of the coiled cable. The resistances of all wires are now under 2 ohms, and the DEC motor is now working no matter how I twist the cable.

Maybe twisting the cable near the DEC board contributed with the little bit of resistance that made the cable switch back and forth from the conducting threshold. But changing the plug solved it.

 

[NEM]

Try swapping the cable that runs between the handbox and the mount end over end.  The LXD 75 cable isn't straight through, it's reversed  That is, pin 1 goes to pin 8, 2 to 7 and so on.

If you change the ends over the signals change over as well.  If the failure message changes then it points to a fault in the cable or the connectors.  I can't remember where I read this, but it's an easy check to make.

 

Noel

[NEM]

I see from the circuit shown in the link Malcolm gave that the RA motor is connected to pins 6 and 7 of the coiled cable.  If you swap the cable ends those lines will be used for the Aux connections which are never used, so the mount may work properly.

Noel

[Pitch Black Skies]

< UPDATE >

I've fixed it!

Decided to try re-solder the wires back myself. It's a poor job, but as they're now enclosed in the case they shouldn't move. I might ask the tech to re-do it with a connector block, but at the moment I'm thinking I might just leave well enough alone.

On the DEC Axis Motor, I noticed that the encoder wheel was missing it's grub screw, it must have been slipping when the motor was turning. I also re-positioned the encoder wheel on the RA Axis motor so as that it is more central between the sensor and Infrared LED.

I assembled everything back together, extremely carefully.. Started it up, went through the menus and this time instead of the telescope slewing at full speed all over the place, it just started gently tracking at the sidereal rate. It was like music to my ears, such a delight.

Thanks so much to all that contributed.

Alan

Encoder wheel grub screw (M2)

 

[malc-c]

That's good news.  I agree that if any repair works then leave it be.  It doesn't have to look pretty.  I presume you either re-flowed each solder joint, or did you swap any wires over.  If it was a reflow then I would be seeking some redress from the tech guy as clearly he didn't do a decent job in the first place.  However I suspect the main cause was the encoder.  If the board can't read the encoder then it won't know its position and will report "I'm lost" back to the handset  

Well done

[Pitch Black Skies]

44 minutes ago, malc-c said:

That's good news.  I agree that if any repair works then leave it be.  It doesn't have to look pretty.  I presume you either re-flowed each solder joint, or did you swap any wires over.  If it was a reflow then I would be seeking some redress from the tech guy as clearly he didn't do a decent job in the first place.  However I suspect the main cause was the encoder.  If the board can't read the encoder then it won't know its position and will report "I'm lost" back to the handset  

Well done

Thanks malc,

I just melted the existing solder and stuck the existing wires back on. To be fair, the techs job was a lot neater than what mine is now, plus the wires are extremely thin, fragile and old.

In trying to sort the grub screw problem I accidentally snapped 3 of them. They can't tolerate much movement at all or they will snap. I was actually holding my breath at times when re-assembling it, so fragile.

Having said that, if they were on a new connector block, I'd imagine they'd be a lot stronger.

Think I'll just let it be, just glad to have it working.

[pete_l]

On 17/09/2021 at 12:13, Pitch Black Skies said:

plus the wires are extremely thin, fragile and old.

You could take a leaf out of the chinese electronics manufacturing handbook and cover all the wires in hot-melt glue!

[faulksy]

On 17/09/2021 at 07:53, Pitch Black Skies said:

< UPDATE >

I've fixed it!

Decided to try re-solder the wires back myself. It's a poor job, but as they're now enclosed in the case they shouldn't move. I might ask the tech to re-do it with a connector block, but at the moment I'm thinking I might just leave well enough alone.

On the DEC Axis Motor, I noticed that the encoder wheel was missing it's grub screw, it must have been slipping when the motor was turning. I also re-positioned the encoder wheel on the RA Axis motor so as that it is more central between the sensor and Infrared LED.

I assembled everything back together, extremely carefully.. Started it up, went through the menus and this time instead of the telescope slewing at full speed all over the place, it just started gently tracking at the sidereal rate. It was like music to my ears, such a delight.

Thanks so much to all that contributed.

Alan

Encoder wheel grub screw (M2)

 

that is brilliant Alan

[Pitch Black Skies]

26 minutes ago, faulksy said:

that is brilliant Alan

Cheers Mike,

I gave it its first light last night.

These are just single long exposure shots.

I don't know anything about stacking, darks, flats, bias, etc yet.

I think it has some good potential, just need to learn how to get the most from it.

 

[faulksy]

m51 looks as good as i seen it 2 weeks ago in brecon. it is in all the merk. m31 is nice