If the spur gears are insanely tight, that could mean that something got in between the gear teeth and locked them up. There are two pinions - the two brass screws in the middle of the spur gears - that hold the gears in place and which allow these gears to rotate. These can be unscrewed - gently with a small wrench. The gears can then be removed and inspected for any foreign particles. They can then also be washed in dish-washing liquid, dried and re-greased. CAUTION! When you do put them back in do not over-tighten the two pinions!!!

While the spur gears are out of the gearbox, try turning the remaining spur gears on the worm end and on the motor shaft. If either of them cannot be easily turned with your fingers, then that would indicate the reason for the motor stall. If the motor gear does not spin freely with your finger, then you may have a bad motor and will have to replace it. If the motor spins freely, just plug in the controller and turn on the power. The motor should begin turning at the sidereal rate (it does not have to be attached to the mating spur gears for this test). Find out as much as you can about where the binding is occurring, and we can go from there.

The gearbox can be removed and sent in for service if you are not mechanically inclined to do the above.

The Dec axis will also not respond if the RA motor is faulty. It does not mean that the DEC motor or gearbox is bad.

Roland Christen

Astro-Physics Inc.

-----Original Message-----
From: Dustin Smith <smithdu@...>
To: main@ap-gto.groups.io
Sent: Wed, Jan 25, 2023 12:22 pm
Subject: [ap-gto] Mach1GTO Motor Stall While Guiding/Imaging

Hey guys,

I have been running my Mach1GTO in my observatory since 2015. It has the CP3 control box with the "V" chip. It was properly balanced during that initial setup and I have not made any changes to the setup since that would affect balance. I re-meshed the gears as part of that initial setup as well, and have not had a reason to re-mesh them again since, so they have been untouched. I also have never oiled/greased the gears. The mount worked flawlessly up until two nights ago. ASCOM driver was v6.4 at the time (today I upgraded it to v6.6 SP1).

I was imaging IC 1805 using Maxim DL Pro v6 and autoguiding to within about +/- 2 arc sec accuracy. I image remotely (I live in Georgia and the observatory is in California) so I was not constantly monitoring my computer during the imaging session. When I did check in on the session, I noticed the last completed image was star trails and the mount had obviously stopped tracking. My horizon limit in Maxim DL was set to 15 degrees above the horizon, and the target object was 11 degrees above the horizon when I noticed this, so figured that's why the mount had stopped tracking. However, I also noticed that Maxim DL was still running the image routine (it usually automatically stops imaging whenever the mount hits a limit) and Maxim had completed 11 images since the tracking stopped (the last saved image without star trails was image #4, and images #5 thru #16 all had star trails). The target object was 22 degrees above the horizon when image #4 was completed, so I know the mount stopped tracking at some point before it hit the 15 degree horizon limit. I stopped the imaging routine and attempted to park the mount (I use the Park 1 position) but the mount wouldn't move. Using the manual mount controls in Maxim DL, I was able to move the mount in declination on the N/S axis but it would not move in RA on the E/W axis. At this point the sun was beginning to rise and I had to get my kids to daycare, so I asked a local club member for help. He came out to the observatory, loosened the clutches on the mount, manually placed the mount in the Park 1 position, re-tightened the clutches, and closed the roof of my observatory.

The following day after a bit of sleep, I tried to diagnose the problem. Using the AP ASCOM driver utility, I connected to the mount and tried to slew and immediately got "Motor Stall" errors. Figuring this was a gear mesh issue, I asked my club buddy to re-mesh the gears for me (per the AP manual/guidelines) which he did. That did not solve the problem and the mount still won't move in RA. It also now stalls in the Dec axis as well, however on the Dec axis the mount will move a bit before the the motor abruptly stops/goes silent. He confirmed the indicator light on the control box is yellow/amber (rather than red) indicating a safe mode / motor stall condition per the AP manual.

He sent me the photo below of the RA gearbox and gearbox cover. He said the large spur gear looks crooked compared to the housing, and the spur gears are extremely tight. His words were "The RA assembly is insanely tight. Not the worm gear but the spur gears. I could easily turn the Dec gears by hand, but RA would move a little then get really really tight." He also noted it appears one of the gears has been rubbing against the inside of the housing cover as seen in the photo below.





Another thing I find interesting is the AP driver utility reports the scope as being on the east side of the pier, even though it's in the Park 1 position with the scope on the west side of the mount and the counterweight bar pointing due east. Maybe I'm confused here as I've never paid attention to this readout in the driver before, but shouldn't it be reporting the scope is on the west side?





At this point I'm out of things to check for. Is it possible to adjust the "tightness" of the spur gears in the gear box to get them meshing properly? Is this something I can do or does the mount have to be sent to AP for repairs? I can try re-greasing the gears but I can't imagine that will help with this much tightness, but that's just an assumption on my part.

What do you all think? Any help would be appreciated.

Thanks and take care,
Dustin

--
Roland Christen
Astro-Physics