AM5N Guiding/Tracking Issues?? ZWO AM5N · AstroCapture325 · ... · 34 · 744 · 3

Do you perchance have any guide logs you can share? I suspect I know what the problem is as I too have an AM5N which recently had a major problem, and now it is fixed. I want to verify the exact issue before I tell you what is likely going on, just to be sure I don't give you a false alarm. I want to insure I know what the exact behavior is.

AstroCapture325:

Shawn Thiessen:
Do you perchance have any guide logs you can share?

@Shawn Thiessen Thank you very much for offering to review the guide logs. I have included a "bad" one (July 9) and a good one (July 10) for comparison. It goes without saying that I will be very interested in any conclusions you reach.

PHD2_GuideLog_2025-07-09_220057.txt
PHD2_GuideLog_2025-07-10_215029.txt

Thanks! This helps me out a lot. I've taken a look at the logs and the problematic one is certainly interesting. It looks concerning but it's not exactly like what my AM5N was doing, it's much more gradual and the RA peak in the positive direction is lower than what my mount was doing. A frequency analysis shows a very gradual climb from controlled to out of control as the mount approaches the meridian.

I have a couple of questions for you regarding the configuration of your set up.
1. Are you using the TC-40 Tripod? As sturdy as it is, it does have flexture and will affect relatively heavy payloads.
2. How old is your AM5N? You can get a ballpark idea of its age/when it was assembled based on the periodic error test report provided with your mount (there is a date of when the test was generated). There is a problematic range of AM5N's which are affected by a very similar problem, of which my own AM5N was one.

I don't see how PHD2 settings would cause such large peak to peak deviations, not even if the seeing was the worst seeing in the history of the world. I suspect a physical or mechanical origin of your issue. I don't have any idea why this would happen one night and not the next though unless the end of the good log was long before the meridian flip. Although, my AM5N exhibited similar behavior on a handful of occasions before it erupted into a full blown problem every night.

AstroCapture325:

Shawn Thiessen:
1. Are you using the TC-40 Tripod? As sturdy as it is, it does have flexture and will affect relatively heavy payloads.

No. My rig is at Starfront. It is bolted to a steel pier which is anchored in concrete. Also, my payload is only 17 pounds.

Shawn Thiessen:
2. How old is your AM5N?

My periodic error test report is dated August 2024.

Shawn Thiessen:
I don't have any idea why this would happen one night and not the next though unless the end of the good log was long before the meridian flip.

@Shawn Thiessen  No. The "good log" tracked M51 for about 4 hours after it crossed the meridian. I then switched targets and the "good log" tracked NGC 7380 for about 2 hrs before crossing the meridian and 20 minutes after the meridian crossing with good results throughout, upon which I ran out of darkness.

I did ask the Starfront staff to double-check my cable bundles. They found one area that could be a potential concern so they remediated it, but they did not think it was causing the guiding issue.

Thanks again for looking. I sure hope it isn't a mechanical issue.

Alright, so this makes things a bit more complicated. I find it strange that it would behave the day after acting weird. The mount being at star front makes troubleshooting much more complex. You mount is also just outside of the known problematic range so I'm not inclined to think your AM5N is encountering the same issue as mine.

I'd say monitor it, and keep an eye on what it does moving forward. If it continues, it may be worth while bringing up a support ticket with ZWO. I had to RMA my AM5N for the particular issue it had, I live in Texas too, and ZWO has a repair facility in the states. It was a simple in and out fix fortunately but it does mean you will be out of a telescope for a little bit if it comes to this.

AstroCapture325:
@Shawn Thiessen Looks like there is a problem with the RA motor on some units. Problem with AM5N

I saw the same thing, I think your problem may be with the motor or the tension of the RA belt itself. The issue the OP in this post is experiencing, the extremely high periodic spikes, is what I encountered with my AM5N. The tech who fixed mine told me that for every component he tried to replace on a mount that acted this way, it only fixed the issue temporarily if at all, until he replaced the main board. After he replaced the main board, he discovered the problem went away. I got my AM5N back last week, got to test it the same day, and found the issue was in fact fixed. Either way, I think the most wise approach in this scenario is to open up a support ticked with ZWO and see what they have to say.

Shawn Thiessen:

AstroCapture325:
@Shawn Thiessen Looks like there is a problem with the RA motor on some units. Problem with AM5N

I saw the same thing, I think your problem may be with the motor or the tension of the RA belt itself. The issue the OP in this post is experiencing, the extremely high periodic spikes, is what I encountered with my AM5N. The tech who fixed mine told me that for every component he tried to replace on a mount that acted this way, it only fixed the issue temporarily if at all, until he replaced the main board. After he replaced the main board, he discovered the problem went away. I got my AM5N back last week, got to test it the same day, and found the issue was in fact fixed. Either way, I think the most wise approach in this scenario is to open up a support ticked with ZWO and see what they have to say.

@Shawn Thiessen How long was your mount at the repair facility?