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CEM70 RA and DEC controller retrofit


paul
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This is an update... the boards arrived yesterday, 4 days ahead of their schedule. A quick inspection showed them to be a 2021 week-17 design. 

The short summary is that the board change was simple and quick¬†and it workedūü§©.

 

I pointed my 250mm F4.8 at the Heart nebula in the area of WeBo 1. This is simply processed 1:1 (crop) of a stack of 60x2minute Ha subs under some pretty awful conditions and not the best guiding. Nice round stars, I no longer have tic-tacs.

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Once the boards were changed the mount would not respond to remote commands (e.g. Zero, Park, Goto) but the hand controller equivalents worked fine. A factory reset of the mount via the hand-controller cured that.  Checking the FW, the boards are fitted with a version not yet available for download.

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Here are the new boards, the RA board has the extra PEC header at the top of the board.

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The old boards:

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Compared to the original boards the new boards have minor layout changes, they are missing an unpopulated J2 connector, crystal is in a different package and the 0.33F super-cap is the same capacity but less densely packed. The only obvious difference is the choice of processor - the new boards are fitted with an STM32F103C8T6, the old boards have STM32F373CCT6 (over specified for its task I suspect). All-in-all this is evidence of a maturing and optimised design.

 

There was speculation on other forums that the stepper motor controller on the original boards was suspect. The driver chips on my old and new boards seem identical to me - but counterfeiting has become a significant issue for all manufacturers in the last year or so. Maybe iOptron got unlucky.

 


 

 

 

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1 hour ago, TerryMcK said:

Paul were the replacement boards supplied under warranty and did they come direct from the manufacturer or via the reseller you bought the mount from?

I  wont over share - suffice to say I needed my reseller's help to wake up iOptron and that got things moving.

I was given two options:

  1. Send my boards back to the USA at my cost and they would modify and ship back the boards.
  2. Pay silly money for direct shipment from the factory for new boards and I keep the old ones.

I went for option 2ūüôÉ. Then the airport went in to COVID lock down and 5wks later I had to remind them to ship to me.

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  • 6 months later...

Hello Paul.

 

I am having the same issue with my CEM70 with the V2024 boards and currently have the new upgrade boards on the way.

Question: did your CEM70 also have a ticking or knocking noise about every 1.2 seconds in the RA motor when tracking? If so, did the upgrade boards fix the knock?  My RA motor ticks/knocks when set to tracking (even with the belt off) and I can feel it in my fingers when holding the RA motor, so I'd imagine if I can feel it then the telescope can as well. Just curious if you also had this along with the tracking issue and/or if the vibration from the knock was actually causing the tic-tac stars issue?  Thanks

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Hi Brian, 

I can't be certain. I only recall hearing a tick occasionally, and I didn't link it with the problem. But, I can say haven't noticed it since doing the upgrade. 

 

I've read in other forums the change did make the mount quieter for some people. 

 

I'm speculating but a ticking like you describe sounds like a motor driver issue. (I can't imaging anything else in the mount is moving that fast) It's the driver chip that is being replaced in the board swap so fingers crossed it solves your issue. 

 

FYI the upgrade improved my star shapes but I continued to have guiding issues. In the end I stripped the mount down and reseated the worm screws for both Dec and RA. I now have good guiding too. 

 

Good luck and please update us when you have news. 

 

 

 

 

 

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Yeah I've read too others have said it quieted down the motor but others said it didn't. Some say the stepper motor ticking noise is harmless anyway but I maintain that if I can physically feel it in my fingers, then surely that can't be a good thing so hopefully the new boards make a difference. Glad to hear the boards fixed your tictacs. As far as reseating your worm scews...they just had crud causing issues or just not aligned right? I did clean and re-grease mine but didn't notice any appreciable effect on guiding. 

 

Edited by Brian
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I was getting very erratic Dec behaviour with lagre or small backlash reported and large swings when guiding. 

 

I tried adjusting the mesh but it was either binding or not with no sweet spot. So I disassembled the Dec to look at the worm gear and found that the screw holding the left side of the worm wasn't very tight and I convinced myself the left side was moving as I adjusted the mesh on the right side. I loosened the left screw and moved both sides at the same time towards the gear and clamped them down. 

 

For good measure I checked and did the same for the RA. 

 

The mount is now predictable with the Dec guiding better than RA and consistent with other people's reported performance. 

 

 

 

 

 

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Interesting. I also have inconsistent backlash numbers and occasional random spikes in RA but my balance is always spot on. One time PHD2 guide assistant tells me my backlash is 1200 then next time it says 150 or less. I just had it all apart when I cleaned and re-greased the gears and did find three of the screws that hold the big worm gear in place were pretty loose (RA) but I never checked the worm mounting screws. Guess I need to go back in and have another look. 

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Posted (edited)

Those ae very similar numbers to mine.... I think the DEC backlash reported can vary if you don't nudge North before trying to  run GA. That little nugget I missed in reading the docs and only picked it up when I rewatched the official tutorial on Phd2. Not enough clear night's to get scientific though particularly when guiding total rms is consistently around 0.6 with dips below 0.5 at the moment. 

 

I've also now done the famed balencing in the 3rd axis and I've  modified my PA routine by getting as close to 0 in Alt and Az and then putting a deliberate offset in ALT. I understand that minimises the number of Dec corrections switching direction. 

 

I also changed my cable runs to minimise any rubbing of the dew shield cables. 

 

Since the strip down I've only run GA once and it reported around 1200 ms. But my guiding has been a dream. Dec corrections are currently very infrequent compared to RA. I just hope that isn't just exceptional seeing for two weeks and that I really have "improved" things. 

 

People rarely report what their load out is but often it seems the good reports go with wide field refractors! They don't need sub arc second guiding anyway. And I'm sure locations are in Central USA where conditions are less turbulent than the UK. I need sub 0.6 to get the most out of my scope. 

 

If I have killed the random noisy Dec and RA movements I won't care to investigate which change was most significant. 

 

If it is just seeing then I can know to stop tinkering and that I don't now have a lemon mount. 

Edited by paul
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That's the thing with me too, I know I am seeing limited as the skies where I am in the US typically are less than ideal and I need to stay .7ish or lower which is totally doable, but if I could stay consistent at .5-.6 without the tic tacs at 910mm I'd be totally happy with that.  I'm not a number chaser just for the sake of numbers, but I've discovered how critical things become at longer focal lengths. Prior to the new Stellarvue 910mm I was imaging at 250 and 550mm with a asi294mm with no issues but with the new scope and new QHY268M I just got, my imaging scale is much lower with that rig.

 

I was not aware of needing to nudge north before running GA. I need to re-read that as well.  Nor was I aware of offsetting the ALT just a bit to help the dec switching corrections....good to know, I will check that out. 

 

I guess I'll just get the new boards in place and see where it goes from there. Ioptron does say the upgrade boards are supposed to improve guiding overall and eliminate the oscillation issue so hopefully that's the case for me as well and I'll be done with it. That RA motor ticking still bugs me though but ioptron tech said I can send it in for them to check to see if it needs replaced. We'll see.

 

Man, things were so much simpler back when I didn't know any better! 

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  • 2 weeks later...

Well, I got the upgrade boards installed as well as a new RA motor as ioptron support said the motor shouldn't be knocking like it was. Interestingly, just installing the new upgrade boards did indeed stop the knocking issue and the motor runs smooth. I did go ahead and replace the RA motor as well though because the new motor is a great deal quieter. Now I just have to wait for a clear night to see if my guiding improves at all. 

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