Houston, we have a problem.........(Updated)

It had all the makings of a beautiful clear skies night. An opportunity to get an extended astrophotography session. Being still new to the hobby with mountains still to learn, taking every advantage to get out and try different settings, equipment configurations, look for different targets and all the associated things that go with it.

I was planning on setting everything up, getting 'excellent' polar alignment (this is a grading on the application SharpCap that I use to do aligning and image stacking). Follow this with a 2 star alignment or a plate align, and decide which target I was going for, then stop and put the camera battery back on to full change before coming out again and getting a long imaging session.

Hauled all the telescope stuff outside and set up as usual. Got the polar alignment done, searched the skies for a target or two and set it off on an imaging run.
Bresser Newtonian - NT203/1000 with EXOS-2 Goto Mount
At this point, I was still not using the autoguider, it had arrived the day before, but I had not had time to see how to use it and didn't want to waste a clear night on learning something new.

I left everything running and headed inside, as I normally do, and come out periodically to make sure everything is ok, it still running, battery not flat, laptop not died or tried to update etc. etc.

I headed out for a periodic check and found the scope had headed off in some random direction, and was only stopped by the cabled pulling it tight. It had managed to dislodge the gear wheels on the declination motor and mount drive cog, but the motor was still turning freely, with the cog just spinning round.

I called it quits for the night and hauled everything back inside. I would need to look at refitting / aligning/checking everything in the daylight.

Diagnosing Time

The next day I set everything up again inside, re-aligned the declination motor drive and made sure everything was running smooth. Unfortunately, things were not so good.

When slewing the declination axis, the motor was running very fast. Regardless of what slew speed was selected, it was fast. The right ascension axis was fine, and continued to work correctly.

I checked all the cabling, all was good. I next unloaded the mount, taking off the telescope and the counterweights and just ran it bare to see if that made a difference. Sadly, no.

Ok, maybe there was moisture or a bug or a bit of debris inside the declination housing that was maybe giving a dodgy signal or shorting the PCB. I removed the declination housing off the scope, took up to my office and stripped it down, all looked good, nothing appeared to be wrong, it was bone dry, no visible component issues, no funny smells, gears turning smoothly, the optical encoder was clean with no signs of problems or blockages on the slits. Rebuilt the housing, refitted it back onto the  mount and sadly still the same issue.

I tried to do a backlash correction setup, this compensates of the gear slack when you change direction. This was no problem on the RA, but was impossible on the DEC because there was no fine movement on the scope, it was just full speed. Even try to just pulse the handset button didn't give small enough movement.

Maybe a corrupt setting, performed a reset from the handset controller. Nope.

Maybe the firmware was corrupt? Tried to reflash the firmware, but no matter what I tried on both a laptop and a PC, using the supplied official USB to serial dongle and cables (and upload adapter) and also direct to serial comms port on the computer, it just wasn't having it. The software just refused to read the device ID. I tried to use FlashMagic to see if I could even just connect, but it failed on autobaud errors. Although, connecting to the ASCOM POTH software it communicated fine.

I was at a loss what else I could do. I probed the PCB and watched the voltages and test points for signal changes, and the only thing I could find, was the one of the encoder signals wasn't changing between low and high states as the encoder wheel connected to the shaft was turning. Now, I dont have the source code for the microcontroller so no idea how this would effect the mount operation, or even if that signal was being used at all.

Here is a video of the mount issue. In it, I compare the RA operation (ok) vs the DEC (faulty) operation and they used to function the same before the fault developed. You will also see a second fault that manifests on the DEC axis, whereby if I hold down one of the DEC direction keys, the mount travels at speed, then just winds down to some intermediate speed until you take finger off the button. Definitely not how it is meant o behave.

I contacted both the manufacturer and the reseller in Germany and they [the reseller] sent out a replacement GoTo set for me to swap out and send the defective units back. It is still under warranty only being a couple of months old. Originally, the manufacturer wanted the whole mount back, but that is really not sensible as the unit is heavy and would cost a fortune in courier costs. They need all the components to work out of it is the handset or the motor assembly. The reseller agreed that this was excessive and agreed it was better to send out a GoTo kit and to swap everything out and then return the faulty set back.

And that is current status. Waiting for the warranty equipment to arrive.

Update: 14th May

Still waiting for the replacement warranty equipment to arrive. According to the postal tracking it has at least left Germany (12th May) so for normal post, this means probably another couple of weeks for it to arrive.
In the meantime, I did order myself a complete new GoTo kit from another supplier and couriered this into Cyprus. I thought at least this will allow me to still continue using the scope, and would mean I would have spare parts should anything like this happen again.
The kit I ordered duly arrived and I swapped out all the parts and all appeared to be ok. Appeared to be.........

A near identical fault occurred again although the it didn't appear as harsh, it was still evident that it was there. By now I was raging.......walking away for a cooling off period!

Having gone back to the mount again the following day, I checked everything over. And it all appeared to be ok! Everything was working as it should, the slew speeds were all okay, it all sounded ok. Magic, maybe it wasn't the same and it was just a new glitch.

That evening I took everything outside and tried to setup the mount.......tried being the operative word. For whatever reason, the fault was back again. Over the next 24-48 hours, I checked the gear, tried different things and it was definitely intermittent. I was at a loss. I did notice that on one of the occasions the red power LED on the RA unit was flickering, was this maybe power related?

Now, I am just going to wait for the warranty equipment to arrive, then do a comparison of the electronics and signals and see if I can work out what is failing, or at least see if I understand what is going on.

You know when your not exactly sure when somethings happens, or it may be coincidental, but does raise doubt in your mind? Well, I got this feeling on this occasion.

At the time I noticed the fault start, I had been using APT and done a plate solve and pushed the sync coordinates back to the mount. I noticed that the position that then was reported by the mount was completely different to that reported by the computer. However, that is one thing that I have noticed with this mount is that the position coordinates on the handset, have never matched any coordinates when connected by ASCOM or direct to the mount. Now, they have never been correct since day one of owning the mount, and I have never been able to work out what should the settings at the software side be set to, between the JNOW or J2000 or other coordinate systems. So, is something happening during the coordinate sync that is screwing up the mount? I don't think so, and put this down to the coincidence...

Update: 21st May

Still waiting on post.....


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