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G11G DEC Stall

 

Could the old board be sold to someone who would either fix it or use it for parts to repair others?? (I am not the one, but surely it's some use to someone.)
 

Thank you all again for the incredible amount of background and help! I talked to Michael Herman in detail on the problem and it was decided that likely the best course of action is a replacement board.
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As John Kmetz pointed out a replacement board used to be $300 which imo is a very fair price or a board with common parts and in production so long. It is now $700 for just the board.?

Sometimes it is a trade off of time vs money with enjoyment of a hobby, and in this case I do not have the time go down a potential rabbit hole with the board and miss out on the imaging season in Florida. I skipped last years imaging season to build my new observatory so I’m really looking to start imaging again.?

I’m certainly confused why the board is so expensive now and it leaves a bad taste in my mouth but it is what it is. I was also unable to get a hold of anyone at Losmandy since the beginning of this post (email or phone). The board was ~7 years old and always kept in an environmentally controlled environment. My observatory has both an air conditioner and a dehumidifier.?

Thank you all again for your help and giving so much to the community. I’ll report back if this is the fix. Looks like the replacement board shipped out today.?
 

Paul is totally correct.?? In general all Gemini's are repairable, 1s and 2s. ?? The only thing holding back some repairs may be PCB corrosion or intermittent faults!??? Older G1s are mostly a cake walk but some parts are getting to be a supply issue, also aged PCBs' and moisture are its enemy to its tracks and Pads (after decades of user service).??? Since covid, electronics parts have either become obsolete or increase in price for repairers. ? Its an immutable fact an G1 "H" bridge was $11~$15 AUD ...nowdays $61 AUD and getting rare to source.??? Repairers cannot buy from fleabay...the reasons obvious thus must buy from proper spare parts houses! ?? Easier for Losmandy as they buy parts in 1000's....plus some.
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The equivalent "H bridge" IC on the G2, are now a little cheaper ~$15 AUD. ? But it’s not an easy IC to replace due to its base thermal heat sink pad. ? ?It’ll test even the best skills.?
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Losmandy/Axeox made these PCBs easily accessible to replace ICs aka "repairable".?? But due to the nature, especially, G2s. SMD ICs R&R and firmware can be tricky and more specialist in nature for repairers to perform.? I've seen some damage that defies belief but managed to be repaired.? All repairers, Losmandy, others, Paul et el can do, R&R like this.
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But when you see things like this....see pic......Little did I know that it also took out the 144pin ARM (though I had suspicions and told owner this before starting) ...but R&R'ing that IC (easy enough) then ARM not so easy.....(then doing ARM boot-loader and fimware), Rene' saved me (once again) on that.? This was a more difficult repair but, it's was done dusted and returned fully repaired and at a fraction lower costs of a new board.? We are more and more becoming a "throwaway society" which is sad to see.?
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Bad drive issues on the Gemini...can be many issues caused by many things:.... but these are made to be repaired and servo mechanism is "bread and butter" stuff repairs for those who know the cct'try.? I enjoy doing repairing such......giving the community something back as it has given me so much in return.
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And no that crater is not by me....it vaporised the top of the ST4 interface buffer IC and blew it off and damaged the ARM processor.?? This PCB was fully repaired, still works today, at a fraction of replacement cost.? Still I understand some users like to have spares, so the are not without.? If you do "throw in a spare"...send your old board for repair...you will be surprised and may need it again some day!.
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--
Brendan
 

The problem with a single axis is often caused by the PIC controller (the same one that was programmed with the L6 release). There are two of them, and it's a small SMD chip, not easy to replace without some experience or expert guidance (thank you, Brendan!) It is much cheaper to replace than getting a new board. Our helpful can all do it, so don't assume you need a whole new board if just one of the axis isn't working with a motor that is otherwise functional.
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Regards,
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? ?-Paul
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On Thu, Oct 31, 2024 at 12:31 AM, John Kmetz wrote:

This whole situation sounds familiar, and my final fix was to replace the Gemini 2 PC board. That was several years ago when they were only $300, but now they are much more (see the Losmandy website). I did follow Brandan's helpful advice at that time, but we never found any cracks in the solder joints or the PC board, ergo process of elimination. The board is not that hard to remove, 4 screws on the cover and 4 holding the board inside the case - just for inspection.
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The only other things that might cause a stall after a good balance would be too much tension of worm against ring gear, depletion of lubricant, or too low a voltage in the supply. I switched from the standard Losmandy 15V adapter to the Michael Herman-built 17V unit, which helps to power through the tight spots with a little extra motor torque.?
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Good luck Fritz.
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John
--
 

This whole situation sounds familiar, and my final fix was to replace the Gemini 2 PC board. That was several years ago when they were only $300, but now they are much more (see the Losmandy website). I did follow Brandan's helpful advice at that time, but we never found any cracks in the solder joints or the PC board, ergo process of elimination. The board is not that hard to remove, 4 screws on the cover and 4 holding the board inside the case - just for inspection.
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The only other things that might cause a stall after a good balance would be too much tension of worm against ring gear, depletion of lubricant, or too low a voltage in the supply. I switched from the standard Losmandy 15V adapter to the Michael Herman-built 17V unit, which helps to power through the tight spots with a little extra motor torque.?
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Good luck Fritz.
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John
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_____________________________________________________________________________________________________________________________________________________________________________

Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, NINA, Sequence Generator Pro and PixInsight user
 

Fritz
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here is a image of the old STD motors.?? These components on the motor were for protection in Gemini 1 system and they can interfere with Gemini 2 encoder reading thus you "Can" get stalls.?? In fact I have seen them *these components on these motors) degrade over time and exposure to moisture.? So if you have these motors.?? The possible fix is remove the Zener Diodes (D1-D3) leave their space blank.?? Also remove F1-3...but jumper across their old pads with a short think wire link (so it won't hit the bottom of the motor housing)...Clean up with isopropanol and PCB resist....if you have some.
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Of course if you have HT motors....forget the above!
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.............While typing this.......I just learned that no matter what motor is on your DEC, its dead......so sorry its a Main Board issue?? are listed or (depends where you are ) is best option.
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Cheers
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Brendan
--
Brendan
 

One extra thought Fritz is whether you have upgraded to L6 as part of your upgrade work? If so that is a little more sensitive to imbalances.
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I spent a little more time balancing my counter weights with my telescope and was mindful of the following from AP :-
"https://www.astro-physics.info/tech_support/accessories/mounting_acc/balance-to-optimize-guiding.pdf"
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It looks like you have a lot of good input from others so good luck.
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Ken
 

Fritz, swap the Ra motor to DEC and visa versa. ?Did the fault follow the motor or stay in same axes?
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You can do this test with out installing the motors just do it on a bench. ?Mark which motor (and cable) is Ra and which is DEC! ? So as to not confuse them later. ?Which only complicates it all.
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If the fault stayed DEC then try swap cables to see if the fault ?changed axes!
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if in the first test swapping motors, if the fault moved to Ra it’s a motor issue. ? If it moved with the cable it’s a cable issue.?

If it stayed at DEC it’s a mainboard issue.?
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Get back on this pls. ?Also is it a “tallboy Gemini”? ?Some of these suffered hairline cracks between the motor socket on the main board (DEC in this case) ?and these caused all sorts of unusual motor issues. ?

Easily found with multimeter and or close magnifier inspection. ? Even measure from motor to Mainboard PCB pads while flexing moving the Din Cable! ? ?Just a little not a lot, you don’t want to break it…gently wriggle the plug in the socket! ? ?This can identify issues like the small cracks mentioned. ?

These are easily re-soldered but I like to desolder remove the old pin (it uses a cup/pin arrangement, under the socket) and solder in bigger pins.
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But your first step is to swap motors see what it does (wrt to the fault) and get back to us so we can advise further! ? ?Also tell us if it’s a “tallboyG2”?
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Oh, lastly ….are these the , maxon or HT motors?
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Some of the older STD motors, has diodes and zeners on its PCB that can interfere with the running on a G2 but usually only causes sped failure issues. ?But I have seen these components cause faults themselves. ?

So we need to know motor type. ? If it has 3 small fuses and zeners (look like diodes) on it.?
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cheers get back on all this.?
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--
Brendan
 

I’ll have to look into third parties. Had no idea anyone else worked on them. I emailed Losmandy last night so we will see what I get back.?

It stalls at all slew speeds. I run at 200 to begin with (default is 800) for slew speeds to baby the mount with the RC10 on it. The DEC stalls even on very low center or guide speeds.?
 

I don't know Gemini2, so there may not even be an option in there?but in Gemini1, there is an option to change the slew speeds.
It might be worth reducing the slew rate on the DEC axis (if that's possible) and see if that makes a difference.
At least it might tell you if it's mechanical or electric.

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Thanks and Best Regards
Neil


On Wed, Oct 30, 2024 at 11:49?AM Fritz via <fritzlaun1=[email protected]> wrote:
Hey all!
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I just rebuilt my observatory over the last ten months and had my 2017 G11G with Gemini 2 controller safely stored inside my house (A/C).?

I’ve remounted the G11G, but I’m having an issue I’ve never had before. My DEC axis is stalling. The scope is balanced (RC10) and has been used on that mount for years.?

What is very odd is that if I plug in the DEC motor to the RA output on the Gemini 2 it has no issue moving the mount in DEC. At first I thought was then just a cable swap issue. Unfortunately if I only swap the cables and don’t cross the DEC/RA outputs from the Gemini 2 I get the DEC stall error.
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I’m using the power cable I’ve always used (supplied by Losmandy). I also did replace the battery in the Gemini 2 since I remember when that gets low voltage things get… weird. That didn’t seem to have any effect.?

I did take the DEC gear cover off (exposing the two gears) and it’s very easy to spin those and spin the mount in DEC.?

Thank you!
 

I think there are third parties who do repairs also.
 
Edited

Thanks for the quick reply!
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I’ll have to open it up again tomorrow and see if there is an issue with the socket. The socket doesn’t seem loose.?

If I need to send the Gemini 2 in that likely means I won’t get to image this season here in central Florida. Last I talked to Losmandy about getting my G11G upgraded to have a titan RA it was a 6 month turnaround minimum. Obviously not the same thing but doesn’t give me confidence in a fast turnaround.?
 

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This sounds like an electronic failure of the circuitry that drives the dec motor.? The last stage of the circuitry should be the same for RA and dec motors, and your motor works with the wrong one but not the right one.

You might look for loose connections inside, especially a problem with the dec cable socket; otherwise it may be time to send your Gemini off for repair.


On 2024-10-29 20:48, Fritz wrote:
Hey all!
?
I just rebuilt my observatory over the last ten months and had my 2017 G11G with Gemini 2 controller safely stored inside my house (A/C).?

I’ve remounted the G11G, but I’m having an issue I’ve never had before. My DEC axis is stalling. The scope is balanced (RC10) and has been used on that mount for years.?

What is very odd is that if I plug in the DEC motor to the RA output on the Gemini 2 it has no issue moving the mount in DEC. At first I thought was then just a cable swap issue. Unfortunately if I only swap the cables and don’t cross the DEC/RA outputs from the Gemini 2 I get the DEC stall error.
?
I’m using the power cable I’ve always used (supplied by Losmandy). I also did replace the battery in the Gemini 2 since I remember when that gets low voltage things get… weird. That didn’t seem to have any effect.?

I did take the DEC gear cover off (exposing the two gears) and it’s very easy to spin those and spin the mount in DEC.?

Thank you!
-- 
Michael A. Covington, Ph.D.
Consultant, Covington Innovations, Athens, Georgia, USA

 

Hey all!
?
I just rebuilt my observatory over the last ten months and had my 2017 G11G with Gemini 2 controller safely stored inside my house (A/C).?

I’ve remounted the G11G, but I’m having an issue I’ve never had before. My DEC axis is stalling. The scope is balanced (RC10) and has been used on that mount for years.?

What is very odd is that if I plug in the DEC motor to the RA output on the Gemini 2 it has no issue moving the mount in DEC. At first I thought was then just a cable swap issue. Unfortunately if I only swap the cables and don’t cross the DEC/RA outputs from the Gemini 2 I get the DEC stall error.
?
I’m using the power cable I’ve always used (supplied by Losmandy). I also did replace the battery in the Gemini 2 since I remember when that gets low voltage things get… weird. That didn’t seem to have any effect.?

I did take the DEC gear cover off (exposing the two gears) and it’s very easy to spin those and spin the mount in DEC.?

Thank you!

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