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Re: Intermittent electrical power issue on my Obsession (20" f/4, circa 2020) with ServoCat and ArgoNavis

 

¿ªÔÆÌåÓý

Mike,

?

I was having a similar problem where I would lose power in azimuth ¨C whether during a manual slew or in a motor-driven one.? I cleaned and adjusted all of the various parts of the PGB where corrosion or debris could possibly get in and interfere with the circuit, but that didn¡¯t do anything to improve the reliability of the platform long term.? Eventually, I found out that many people were using a spring that went around the central (positive?) post that fit into the bushing in the center of the PGB.? My older (2005) platform did not have this spring.

?

I ordered this spring from Bill at ServoCAT and, with the help of a friend, expanded the central hole that accommodates this post and bushing from ?¡± to 1¡± so it would all fit.? This wasn¡¯t trivial, but with the right tools, wasn¡¯t that difficult, either.? Once it was all fitted, we tested and things seemed to work well with no power drops.? A few days later, I was at the Texas Star Party and the spring worked flawlessly.

?

Go through the steps Gary outlined below, that will get you to what might be ailing you.? For me, it was ultimately the lack of a spring that was the main culprit and adding one of those seems to have made all the difference in eliminating power drops.

?

Good luck!

?

Joe Khalaf

?

From: [email protected] <[email protected]> on behalf of K9RX - Gary via groups.io <amateurK9RX@...>
Date: Saturday, May 31, 2025 at 10:08
?AM
To: [email protected] <[email protected]>
Subject: Re: [ServoCAT] Intermittent electrical power issue on my Obsession (20" f/4, circa 2020) with ServoCat and ArgoNavis

Hello Mike.?

?

Ok... so its not common but it does happen at times. What Steve said would apply if indeed you are drawing a decent amount of current and the line cord were smaller than 18 ga (or very long).?

?

However usually this can be attributed to issues with the PGB.?

?

Here's the blurb that I would send out... I think this should take care of it. Two things stand out: there is a spring loaded cantilevered plate near the center of the floor of the rocker. It has one center flat blade screw. It might be too loose (it can over time work its way out). Do not overtighten it however - if you grab the outer edges and lift it should SNAP back down. The nominal lift distance is about 1/8" or so.?

?

The other are the 2 bushings that the contact rods - from the bottom of that plate - go through. I discuss that below.?

?

?

g.

?

?

ok... first off do you have other items connected to the power rail ¨C the Argo (go to MODE STATUS, ENTER, and see if it says EXT for external or
BATtery), fan, etc? And if so do any of these go out when the ServoCAT¡¯s lights are out? If they do proceed ¨C if they do not then the problem is inside the scope and not the
PGB system at the center of the rocker ¨C i.e. the part that brings power in. It may be the power rail or just cabling.

Does it do it at a particular spot?

-check to be sure the cable in the center back of the ServoCAT, RCA/Phono plug, is plugged in firmly. Also check that it is plugged into the power
distribution rail inside the rocker.

-An intermittent or "resistive" switch in the power rail might cause this - move the ServoCAT power jack so that it is under a different switch.
This is more common with older PGB power rails (with old fashion metal bat switches).

If not these things than more than likely this is an improperly installed PGB system. When installed properly and maintained the system will never drop out (see
maintenance below).

Some of the things I have seen:

-There are 2 wires, splitting off from a cable inside the rocker floor - one goes into the hole where the pivot post is (under the encoder) and it
will be difficult to tell if it is loose - but put a little tension on it with everything powered up and see if you can make the system drop power.
There is also one that goes to the '-' terminal contact plate which is a stainless plate that is spring loaded...this one is obvious - see if it is
loose.
[Note: if you wiggle this one it might break the connection. This is not necessarily an indication of a problem as these dual contacts are spring loaded and
indeed if you lift the pair it will break contact.]

-next see if the negative terminal contact plate is properly put in place - grab it by the ends and lift up evenly, you should be able to get
1/8¡± -3/16" upward movement before it stops, no more. Lifting it WILL break the connection!
Then it should spring snap back down. Note that we've seen a number of these that were improperly installed ¨C the 2 brushes (for redundancy) have to be
vertical to the floor - if one (or both)is (are) cocked or if they are not properly spaced it can hang up and not provide redundancy and lock up the plate which is designed to be free-floating. I've only seen this on bigger scopes - but I've seen and heard of it multiple times. One can remove brush contact plate ( be careful not to lose the spring/center screw!),
remove the 2 brushes and redrill these holes with a 25/64¡± drill bit to provide a small amount of ¡®slop¡¯ allowing any issues with them being too close/far apart
and/or not vertical to correct itself. This has been noted on several systems.
Reassemble these parts and check.

Now it gets a little more difficult ... you'll need to somehow lift the scope off the ground. One way to do this is to get some blocks (2x3 or 2x4 cut into
3" lengths ¨C 8 of these for example) and put these under the body of the rocker at each corner - NOT the ground board feet. If using the 2x3's place one under one
corner of the scope, then another then the last then repeat with a second one to go a little higher - be careful you don't tip it over!!!!! This will
raise the scope enough to allow the ground board to hang down on the pivot post producing a gap between the top of the ground board and the bottom of
the rocker.

-there is a redundancy spring that fits over the pivot post (the post that goes up from the ground board and that the scope turns on)... if this is
missing you may get, over time, intermittent contact. This is hard to see but sometimes can be seen without taking it apart. Use a flash light and shine
it under the floor of the rocker, along the plane of the floor and into the gap between the rocker and the ground board - you should see the reflection from
the pivot post (shiny stainless steel) and if careful the "wrap" of the spring around it. If it is not there or you can't tell then you'll have to
remove the ground board to check for sure...but first...

-there is a plate at the center of the bottom of the ground board - this is where the pivot post attaches to the ground board. In the center of this
plate (not the outside edges) there are 2 screws. We recommend in our instructions that these be installed using loctite - those instructions are
often missed by installers. See if these screws are loose. If so that could very well be the problem. Also there is a cable that goes from the
connection foot connector to this plate. It connects to it and to a small plate with studs near it... the large pivot post plate is the '+' contact,
the smaller plate with studs is the '-' terminal plate. See if either of these are loose. When we build a ground board we put silicone (not caulk) on
these to prevent them from corroding and from coming loose.

Last if all else fails you need to remove the ground board and see if the spring is there. For smaller scopes you can remove the mirror box and turn
the rocker on its side. For larger ones you can possibly get your hand in there with a hex wrench to remove the 2 screws that hold the pivot post,
have the ground board "fall" onto your arm when the last thread is removed and then carefully remove the ground board... this is difficult and even
more so to get it back on - but I've done it a number of times and it can be done. We do have a separate document for removing the ground board ¨C
please ask for it if you are going to go through this process.

[note the ¡®spring¡¯ was added in about late 2005 or early 2006 I believe... and I had faulty instructions on it as I had forgotten to tell people to
enlarge the whole in the ground board to allow the spring to do its thing ¨C if that hole isn¡¯t 1¡±, which it has to be ¨C the spring could easily get hung
up and not do its proper contact (adding redundancy ¨C as designed)]

MAINTENANCE:
-some things that might want to be inspected:
-you can remove the brush assembly, this is the plate that has the 2 screws/brushes and a center screw. Assuming you've checked the above items.
You can remove the connection wire, be careful the lug is not twisted. Then remove the center screw - be CAREFUL not to let this go - as it I spring
loaded! Keep this all together (you can use a wire tie on the bottom of that center screw so that the screw isn't propelled out by the spring). Inspect
the brushes. They should be clean at the bottom. Use fine sand paper to clean the ends if they are not. If the sides are not clean and possibly they
are causing them to stick in the brushes then clean this as well and if so you might want to remove the bushings in the floor and clean inside them.

-If you have removed the ground board you can inspect the top of the stainless contact plate. It is normal for a ring to be seen where the
brushes have been contacting it - but it should not be dirty. Clean if necessary.

-Make sure the pivot post, the main 3/4" diameter stainless steel post that goes up the center, is very clean - no oil or dirt. Use as a minimum soapy
water to clean it (this will clean off any oil residue from the inside of the bushing).

-clean the inside of the main bushing in the center of the floor of the rocker. Use soapy water - be sure it is CLEAN.?

------ Original Message ------

From "Mike Greenhill-Hooper via groups.io" <sally.greenhill@...>

Date 5/31/2025 10:40:54 AM

Subject [ServoCAT] Intermittent electrical power issue on my Obsession (20" f/4, circa 2020) with ServoCat and ArgoNavis

?

Hi,

a couple of times recently when the scope is being moved along its axes, either manually with the motor / clutches disengaged? (e.g. during 2-star alignment) or even during execution of a GOTO command I lose power.? In the first case I hear bleeping (presumably power was lost somewhere and communication is restored when it comes back?). Fortunately as I also keep batteries in the AN unit any alignment / positioning data seems to have been stored and preserved so I can carry on.? When I lose power during a GOTO if I waggle the cables and check the various connections on the ground board the power is restored.? I think I tend to lose power when the scope is moving on the Azimuth axis. When it cut out recently during the GOTO I noticed that the cooling fan had also stopped.? Once the scope is on the target I have no problems with sending guide or jog commands via the hand controller and the object is well tracked. I don't think there is a fault with the power supply going into the telescope.

?

Is this a common problem and does anyone know what might be the cause, please?

?

Mike GH

?

?


Re: Intermittent electrical power issue on my Obsession (20" f/4, circa 2020) with ServoCat and ArgoNavis

 

Hello Mike.?

Ok... so its not common but it does happen at times. What Steve said would apply if indeed you are drawing a decent amount of current and the line cord were smaller than 18 ga (or very long).?

However usually this can be attributed to issues with the PGB.?

Here's the blurb that I would send out... I think this should take care of it. Two things stand out: there is a spring loaded cantilevered plate near the center of the floor of the rocker. It has one center flat blade screw. It might be too loose (it can over time work its way out). Do not overtighten it however - if you grab the outer edges and lift it should SNAP back down. The nominal lift distance is about 1/8" or so.?

The other are the 2 bushings that the contact rods - from the bottom of that plate - go through. I discuss that below.?


g.


ok... first off do you have other items connected to the power rail ¨C the Argo (go to MODE STATUS, ENTER, and see if it says EXT for external or
BATtery), fan, etc? And if so do any of these go out when the ServoCAT¡¯s lights are out? If they do proceed ¨C if they do not then the problem is inside the scope and not the
PGB system at the center of the rocker ¨C i.e. the part that brings power in. It may be the power rail or just cabling.

Does it do it at a particular spot?

-check to be sure the cable in the center back of the ServoCAT, RCA/Phono plug, is plugged in firmly. Also check that it is plugged into the power
distribution rail inside the rocker.

-An intermittent or "resistive" switch in the power rail might cause this - move the ServoCAT power jack so that it is under a different switch.
This is more common with older PGB power rails (with old fashion metal bat switches).

If not these things than more than likely this is an improperly installed PGB system. When installed properly and maintained the system will never drop out (see
maintenance below).

Some of the things I have seen:

-There are 2 wires, splitting off from a cable inside the rocker floor - one goes into the hole where the pivot post is (under the encoder) and it
will be difficult to tell if it is loose - but put a little tension on it with everything powered up and see if you can make the system drop power.
There is also one that goes to the '-' terminal contact plate which is a stainless plate that is spring loaded...this one is obvious - see if it is
loose.
[Note: if you wiggle this one it might break the connection. This is not necessarily an indication of a problem as these dual contacts are spring loaded and
indeed if you lift the pair it will break contact.]

-next see if the negative terminal contact plate is properly put in place - grab it by the ends and lift up evenly, you should be able to get
1/8¡± -3/16" upward movement before it stops, no more. Lifting it WILL break the connection!
Then it should spring snap back down. Note that we've seen a number of these that were improperly installed ¨C the 2 brushes (for redundancy) have to be
vertical to the floor - if one (or both)is (are) cocked or if they are not properly spaced it can hang up and not provide redundancy and lock up the plate which is designed to be free-floating. I've only seen this on bigger scopes - but I've seen and heard of it multiple times. One can remove brush contact plate ( be careful not to lose the spring/center screw!),
remove the 2 brushes and redrill these holes with a 25/64¡± drill bit to provide a small amount of ¡®slop¡¯ allowing any issues with them being too close/far apart
and/or not vertical to correct itself. This has been noted on several systems.
Reassemble these parts and check.

Now it gets a little more difficult ... you'll need to somehow lift the scope off the ground. One way to do this is to get some blocks (2x3 or 2x4 cut into
3" lengths ¨C 8 of these for example) and put these under the body of the rocker at each corner - NOT the ground board feet. If using the 2x3's place one under one
corner of the scope, then another then the last then repeat with a second one to go a little higher - be careful you don't tip it over!!!!! This will
raise the scope enough to allow the ground board to hang down on the pivot post producing a gap between the top of the ground board and the bottom of
the rocker.

-there is a redundancy spring that fits over the pivot post (the post that goes up from the ground board and that the scope turns on)... if this is
missing you may get, over time, intermittent contact. This is hard to see but sometimes can be seen without taking it apart. Use a flash light and shine
it under the floor of the rocker, along the plane of the floor and into the gap between the rocker and the ground board - you should see the reflection from
the pivot post (shiny stainless steel) and if careful the "wrap" of the spring around it. If it is not there or you can't tell then you'll have to
remove the ground board to check for sure...but first...

-there is a plate at the center of the bottom of the ground board - this is where the pivot post attaches to the ground board. In the center of this
plate (not the outside edges) there are 2 screws. We recommend in our instructions that these be installed using loctite - those instructions are
often missed by installers. See if these screws are loose. If so that could very well be the problem. Also there is a cable that goes from the
connection foot connector to this plate. It connects to it and to a small plate with studs near it... the large pivot post plate is the '+' contact,
the smaller plate with studs is the '-' terminal plate. See if either of these are loose. When we build a ground board we put silicone (not caulk) on
these to prevent them from corroding and from coming loose.

Last if all else fails you need to remove the ground board and see if the spring is there. For smaller scopes you can remove the mirror box and turn
the rocker on its side. For larger ones you can possibly get your hand in there with a hex wrench to remove the 2 screws that hold the pivot post,
have the ground board "fall" onto your arm when the last thread is removed and then carefully remove the ground board... this is difficult and even
more so to get it back on - but I've done it a number of times and it can be done. We do have a separate document for removing the ground board ¨C
please ask for it if you are going to go through this process.

[note the ¡®spring¡¯ was added in about late 2005 or early 2006 I believe... and I had faulty instructions on it as I had forgotten to tell people to
enlarge the whole in the ground board to allow the spring to do its thing ¨C if that hole isn¡¯t 1¡±, which it has to be ¨C the spring could easily get hung
up and not do its proper contact (adding redundancy ¨C as designed)]
MAINTENANCE:
-some things that might want to be inspected:
-you can remove the brush assembly, this is the plate that has the 2 screws/brushes and a center screw. Assuming you've checked the above items.
You can remove the connection wire, be careful the lug is not twisted. Then remove the center screw - be CAREFUL not to let this go - as it I spring
loaded! Keep this all together (you can use a wire tie on the bottom of that center screw so that the screw isn't propelled out by the spring). Inspect
the brushes. They should be clean at the bottom. Use fine sand paper to clean the ends if they are not. If the sides are not clean and possibly they
are causing them to stick in the brushes then clean this as well and if so you might want to remove the bushings in the floor and clean inside them.

-If you have removed the ground board you can inspect the top of the stainless contact plate. It is normal for a ring to be seen where the
brushes have been contacting it - but it should not be dirty. Clean if necessary.

-Make sure the pivot post, the main 3/4" diameter stainless steel post that goes up the center, is very clean - no oil or dirt. Use as a minimum soapy
water to clean it (this will clean off any oil residue from the inside of the bushing).

-clean the inside of the main bushing in the center of the floor of the rocker. Use soapy water - be sure it is CLEAN.?

------ Original Message ------
From "Mike Greenhill-Hooper via groups.io" <sally.greenhill@...>
Date 5/31/2025 10:40:54 AM
Subject [ServoCAT] Intermittent electrical power issue on my Obsession (20" f/4, circa 2020) with ServoCat and ArgoNavis

Hi,
a couple of times recently when the scope is being moved along its axes, either manually with the motor / clutches disengaged? (e.g. during 2-star alignment) or even during execution of a GOTO command I lose power.? In the first case I hear bleeping (presumably power was lost somewhere and communication is restored when it comes back?). Fortunately as I also keep batteries in the AN unit any alignment / positioning data seems to have been stored and preserved so I can carry on.? When I lose power during a GOTO if I waggle the cables and check the various connections on the ground board the power is restored.? I think I tend to lose power when the scope is moving on the Azimuth axis. When it cut out recently during the GOTO I noticed that the cooling fan had also stopped.? Once the scope is on the target I have no problems with sending guide or jog commands via the hand controller and the object is well tracked. I don't think there is a fault with the power supply going into the telescope.
?
Is this a common problem and does anyone know what might be the cause, please?
?
Mike GH
?
?


Re: Intermittent electrical power issue on my Obsession (20" f/4, circa 2020) with ServoCat and ArgoNavis

 

¿ªÔÆÌåÓý

HI Mike,

We had a similar problem of losing power during a slew. It was determined that the power source / power brick was too far away from the scope because of? a long cord. When we removed the long cord and moved the power brick closer to the scope, no more slew problems.

?

Just a thought.

Steve Goldberg

?

From: [email protected] <[email protected]> On Behalf Of Mike Greenhill-Hooper via groups.io
Sent: Saturday, May 31, 2025 9:41 AM
To: [email protected]
Subject: [ServoCAT] Intermittent electrical power issue on my Obsession (20" f/4, circa 2020) with ServoCat and ArgoNavis

?

Hi,

a couple of times recently when the scope is being moved along its axes, either manually with the motor / clutches disengaged? (e.g. during 2-star alignment) or even during execution of a GOTO command I lose power.? In the first case I hear bleeping (presumably power was lost somewhere and communication is restored when it comes back?). Fortunately as I also keep batteries in the AN unit any alignment / positioning data seems to have been stored and preserved so I can carry on.? When I lose power during a GOTO if I waggle the cables and check the various connections on the ground board the power is restored.? I think I tend to lose power when the scope is moving on the Azimuth axis. When it cut out recently during the GOTO I noticed that the cooling fan had also stopped.? Once the scope is on the target I have no problems with sending guide or jog commands via the hand controller and the object is well tracked. I don't think there is a fault with the power supply going into the telescope.

?

Is this a common problem and does anyone know what might be the cause, please?

?

Mike GH

?

?


Intermittent electrical power issue on my Obsession (20" f/4, circa 2020) with ServoCat and ArgoNavis

 

Hi,
a couple of times recently when the scope is being moved along its axes, either manually with the motor / clutches disengaged? (e.g. during 2-star alignment) or even during execution of a GOTO command I lose power.? In the first case I hear bleeping (presumably power was lost somewhere and communication is restored when it comes back?). Fortunately as I also keep batteries in the AN unit any alignment / positioning data seems to have been stored and preserved so I can carry on.? When I lose power during a GOTO if I waggle the cables and check the various connections on the ground board the power is restored.? I think I tend to lose power when the scope is moving on the Azimuth axis. When it cut out recently during the GOTO I noticed that the cooling fan had also stopped.? Once the scope is on the target I have no problems with sending guide or jog commands via the hand controller and the object is well tracked. I don't think there is a fault with the power supply going into the telescope.
?
Is this a common problem and does anyone know what might be the cause, please?
?
Mike GH
?
?


Re: Servocat unit not responding

 

You have problems with the power supply and probably with the electrical network. Use only batteries.


Re: Servocat unit not responding

 

?
Due to work and travel, I only got back to debugging this recently.? I sent in my new ServoCAT unit to Bill and he ended up having to replace the mainboard (he did this under warranty, which I really appreciate).
?
I also tried replacing the lithium battery in the Argo Navis, but the display still doesn't come on.? I've tried both with batteries and with two different 12v external power supplies.? Anyone know where I can get someone to take a look at the unit to see if it can be repaired?? I've tried contacting Wildcard Innovations, but haven't been successful,
?
Cheers,
- Rajeev
?


Locked Re: LiFePO4 battery

 

The description is how to use the system and how to change the settings for optimal use. It is not a detailed technical description.?


Locked Re: LiFePO4 battery

 

I agree. This should be given in the description. That there is not only a gearbox backlash, but also an uncontrolled cable backlash.


Locked Re: LiFePO4 battery

 

Its not a perfect system! It is afterall a retrofittable kit on an EXISTING telescope! Yes it can vary. If you want to always optimize you can figure out what counterweight is needed for each eyepiece. I use a digital luggage scale to measure the force needed to move the scope up or down at various positions.?

...but most people just choose to use their scope





------ Original Message ------
From "alg via groups.io" <alg@...>
Date 5/29/2025 8:17:06 AM
Subject Re: [ServoCAT] LiFePO4 battery

And one more thing. You can load the telescope with a heavy eyepiece with paracorr ~1.5 kg, or with a light plossl. The backlash will be different.


Locked Re: LiFePO4 battery

 

And one more thing. You can load the telescope with a heavy eyepiece with paracorr ~1.5 kg, or with a light plossl. The backlash will be different.


Locked Re: LiFePO4 battery

 

This is easy to check. Put rubber pucks as feet on a balanced large telescope. And it will react differently depending on the height.


Locked Re: LiFePO4 battery

 

Actually the ServoCAT instructions do say to balance the ALT axis. If this is done the force is basically the same.?




------ Original Message ------
From "alg via groups.io" <alg@...>
Date 5/29/2025 7:50:33 AM
Subject Re: [ServoCAT] LiFePO4 battery

Here we have another conclusion. The weight that the telescope lifts from the horizon will be greater than when it is near the zenith. Therefore, the play in the cable will be different, and it cannot be compensated for by only one value.


Locked Re: LiFePO4 battery

 

Here we have another conclusion. The weight that the telescope lifts from the horizon will be greater than when it is near the zenith. Therefore, the play in the cable will be different, and it cannot be compensated for by only one value.


Locked Re: LiFePO4 battery

 

Ok.
i.e. you want to say that if I hook the cable to a rigid tensioning mechanism (for example on screws) there will be no backlash? I can check this, it is easier to do than rubber rollers under Alt bearing. But does it make sense?


Locked Re: LiFePO4 battery

 

Youngs Modulus changes by 5% from -10¡ãC to +25.... more than likely there were other things that were changing due to temperature.?
?
g.
?


Locked Re: LiFePO4 battery

 

And we're talking about almost zero backlsash. Otherwise, there's no point in investing in harmonic gearboxes. All the best to everyone. I'm going away for a long time due to a complete redesign of the Alt drive.


Locked Re: LiFePO4 battery

 

No, it does not work without a spring. Tested at different temperatures. At low temperatures, additional spring tension is needed.


Locked Re: LiFePO4 battery

 

Hello.... would you mind please passing along the name? Thanks.?
?
So - indeed the spring will introduce some backlash. Ideally, if it is the proper spring tension (extension), it will be minimal but this relies heavily on how much static friction the axis presents. If very low then the lash will be near zero. I designed it this way for two simple reasons - because a) to get Obsession to agree to install the product on their new scopes (we're talking late 2002 now) the system HAD TO BE retrofittable onto existing telescopes. It could not be a 'custom' design and b) because the end user had to install the system I had to have some small amount of compliance adjustment for the cable drive. Getting the end user to make the perfect length cable would have been impossible. Ideally if low friction one doesn't need the spring - but the (opposite/free) end of the shaft of the roller should then be held to take up the tension caused by 'full tension' in the cable. So it works - and works well as a retrofit.?
?
Gary Myers
StellarCAT
?


Moderated ServoCat on harmonic gearboxes

 

Go for it, gentlemen.


Locked Re: LiFePO4 battery

 

Yes. The ServoCAT can handle up to 16V without a problem.?
?
Gary Myers