Coronado solarmax 90 II internal tuner repair

[davelilis]

Hi everyone,
I got a secondhand coronado solarmax 90 II recently and it shows some great surface detail and prominences, but turning the richfield tuner had no effect, it showed a decenet h-alpha view but as I'm sure you all know, you need to be able to tune the filter to see different details.
The tuner felt very rough to turn, and when I removed the focuser and looked up the tube, I could see the entire etalon turning when I turned the tuner !!
I wasn't happy to leave this as is and felt I could have a go at fixing this once I saw Bob Piekiel's post describing how to dismantle the scope
viewtopic.php?t=9499

Sorry in advance for the eassy, but if you're having the tuning problem I had, then this is the solution but please make sure your BFxx diagonal doesn't have the rust issue first.
This is not a modifiction, it is a repair, and you use the following information at your own risk.

I refer below to pics I put up on flickr, at this link
https://www.flickr.com/photos/61288385@ ... 0302736104

I was able to take off the focuser by hand, no problem, but the black ring the focuser screws into was stuck tight, pic1 and 2.

1 by D Lillis, on Flickr

2 by D Lillis, on Flickr

I have a heat gun and 2 strap wrenches, I then proceeded to heat up the black ring very carefully, up to 60 degrees celsius, at that temperature I was able to remove the black ring using the strap wrenches, needles to say I didn't have the strap wrenches in place when I was heating the black ring. I was carefull not to apply any heat directly to to gold paint, I didnt want to damage the finish. The strap wrenches use rubber straps that melt at 165 celsius, so they were safe to use in this instance.

In pic3 and pic4, joint A is what was screwing/unscrewing when I turned the tuner, this should never turn, this is where the etalon cell is attached to its holder.

3 by D Lillis, on Flickr

4 by D Lillis, on Flickr

In pic5, you can see the small (lucky for me) amount of red threadlocker glue used, I had to use the strap wrenches to get the tuner off the etalon cell, I didn't apply heat in fear of damaging the etalon, the strapwrenches made short work of it anyway.
In pic5, you can see the holder, the etalon cell and the tuner, the only thing that should turn when tuning is the tuner.

5 by D Lillis, on Flickr

Pic6 is the eyepiece side of the etalon, pic7 is the sunside of the etalon, there isnt much holding in the etalon on the sunside, only some silicon dots on the side by the looks of it, apparently this is normal. DO NOT GO NEAR THE ETALON GLASS, DO NOT DISMANTLE THIS CELL.

6 by D Lillis, on Flickr

7 by D Lillis, on Flickr

So what went wrong here?, what caused the previous owner to tighten the tuner soo tightly that the tuner got bonded to the etalon cell, and when he loosened the tuner, he was actually unscrewing the etalon cell from its holder (pic4) and causing the squeeking rough noise when "tuning".... I had a look at the pin on the tuner (pic9)

8 by D Lillis, on Flickr

9 by D Lillis, on Flickr

and you can see that the pin doesnt protude alot towards the etalon, and on pic10 there is alot of the thread visible on the sunside,

10 by D Lillis, on Flickr

I was able to easily unscrew this center pin and you can see the red threadlocker (pic 11),

11 by D Lillis, on Flickr

this red threadlocker had failed and the pin had unscrewed itself from use over the years, requiring the previous owner to screw in the tuner more and more until one day the tuner hit the end of the thread and got stuck on the etalon cell !!

12 by D Lillis, on Flickr

So I put the center pin screw back in with fresh threadlocker, pics 13/14, put it all back together, care was needed to have the center pin screw at the right depth, about half ways, too far and the tuning bolt (the one you hold when turning) would not fit in its slot, too little and I'd be right back where I started. I didnt threadlocker anything else, there is no need.

13 by D Lillis, on Flickr

14 by D Lillis, on Flickr
I got some good gaps in the cloud this afternoon, and THE THING WORKS !!!, took a few minutes to find the right tuning region, but wow, this thing works great, a good flat even field of view, promenences and filements, granulation and crazy detail around the main sunspot visible, all right there to see, to say I'm delighted and very relieved is an understatement.

To sum it up, the threadlocker failed on the center pin of the tuner, maybe due to heat as it's on the lightpath from the primary, causing the previous owner to tighten the tuner more and more until it jammed with the etalon cell leaving the scope showing a singular untunable h-alpha view. I think this is a early 20-teens scope, so has had a fair bit of use and exposure.

To have a metal mechanical part using threadlocker glue, exposed to concentrated heat from the primary..... I'm not sure David Lunt would approve if he was still with us. IF Meade had put a cap on this center pin with something like tinfoil at the top, to reflect the heat away from the center pin, I think would have been a good move.
I might put a proper sized tinfoil disk on the center of the primary, to have the center pin in the shade.

Anyways, if this happened to my solarmax90 II, it can happen to yours, I hope the above will help you if you have the same problem.

Regards,
Dave.

[marktownley]

Hi Dave

Hope you don't mind, I embedded the photos.

If only the thread lock would fail for all the 1000's of PST modders here

Mark

[davelilis]

No problem at all Mark, that works alot better.
I hope this saves someone else the hassle I had trying to figure this thing out.
As for threadlocker, heat and a good strap wrech is your only chance, with the obvious burn, melt, destruction, screaming and shouting risks..... I was sweating bullets

[astroshot]

Dave,
Great to finally have you here on the dark (bright!) side!
I know you've looked through my Solarmax90 a few times so I'm glad you finally made the plunge.

Brave man to do that mod, but it's clearly been a great success for you!
This post will be really useful to anyone else with similar issues in the future.
Can't wait to have some clear weather and we'll try to meet up - looking forward to seeing what this scope can deliver.
Michael.

[DeepSolar64]

Dave,
I have a SolarMax II 90 and a SolarMax II 60. This really makes me think and worry a bit. I would be so afraid to take my scopes apart. You certainly have skill and courage.

I thought the objective had an ERF coating to reduce the heat load on the scope. Thankfully the DS etalon does have a red ERF.

James

[davelilis]

I thought the objective had an ERF coating to reduce the heat load on the scope. Thankfully the DS etalon does have a red ERF.
James

Hi James,
It might do, it has coatings but I dont know if they block IR. The red thread locker was completely disintegrated on the pressure screw, so the only thing I can put it down to is heat.
Taking the scope isn't too bad a job, now that you have pics to help you see what to expect.

[davelilis]

Dave,
Great to finally have you here on the dark (bright!) side!
I know you've looked through my Solarmax90 a few times so I'm glad you finally made the plunge.

Brave man to do that mod, but it's clearly been a great success for you!
This post will be really useful to anyone else with similar issues in the future.
Can't wait to have some clear weather and we'll try to meet up - looking forward to seeing what this scope can deliver.
Michael.

Hi Michael,
Yes, it was abit of a bareknuckle ride cos I didnt know what to expect or what was threaded into what, but once I had it dismantled, I could see it is fairly simple mechanically. I'm definitely coming over to the bright side of the force lol, I'm liking the "not freezing to death" and zero sleep depreviation involved in solar viewing.

To give you a rundown of the views....
Single stack views through this thing are really bright, I'm camparing it to a Lunt60 which I've here aswell, there is no contest between the 2, the 90's aperture beats it easily, as it should, but I was surprised at how much more detail I could see. The field illumination when the Sun is cented in the fov is even enough not to cause me any trouble, the tuning is good and very smooth, The proms are good and sharp, no optical issues. It would be interesting to see how this compares to your SM90 filtered TEC, my mind is a little rusty about what the exact views through yours were like, except that they were fab, it was years ago. The older/orig SM90s are hard to beat by all accounts.

Double stack mode is a very diffent experience, it's alot darker, and I mean ALOT darker. You have to earn the right to see this view properly. I use the double stack filter tilt to get annoying reflections of the Sun out of the fov and then use the richfield to get it on band and then re-tweak the single stack richfield, and whoaa, the disk detail pops, especially around any sunpots present
Two things about double stack,
1, you absolutely need a dark cloth over your head to block out all daylight, the view is dark.
2, the proms are worse and the disk details are better, as expected tbh.

As you found wiht your solar scope setup, the binoviewers are 100% essential , especially in double stack mode, the differance in what you can see is very dramatic with vs without them.

As for the focuser, I'm not a fan of it and I've a rack and pinion focuser ordered, the weight of the binoviewers tends to bind the helical focuser threads, The panoptics reach focus with the binviewers without and barlow/powermate, but the zeiss's need around 15mm more intravel

[DeepSolar64]

Dave,
In single stack the view is bright through my SMII90 but not so much as to totally wipe out details on the disc. The proms stand out in bright high-resolution against a relatively dark background. The view through mine while double stacked is dimmer than in single stack and certainly shows more disc contrast than single stack does but is not as dark as you describe using yours. I can also often see decent prom detail as well in DS but I cannot see the fainter proms as I can see in SS. I wear only a wide brimmed hat to shield my eyes from direct sunlight when viewing, even in double stack. It works just fine for me.

The only bitch I have with the SMII90 is I find it hard to get an evenly illuminated/tuned disc, especially in DS. The scope certainly has a sweet spot! This is especially apparent while imaging. But some of it may be my apparent lack of skill.

James