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Nexstar 4 woes

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#1 darkmatt'r

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Posted 19 April 2019 - 09:16 PM

G'day Folks!

 

My first post here, so please forgive me if I use some odd language. Straight up I am in need of the Nexstar wisdom! I recently purchased a Nexstar 4 GT (It says GT in the hand controller at least) and I have run into a few problems. It is an old telescope, I didn't realise how old until I started to dig and discovered why the previous owner was being so coy about when she purchased the telescope!

Firstly I noticed with its first evening out, that the vertical slew would occasionally cut out. Then a few days later, going through settings on the hand controller, the display fadded out. At this point I was pretty distressed as I thought the hand controller was dead. I then discovered that I could still slew in all directions and when I did this, the display returned to life! I decided to do some research and found this Youtube clip: https://youtu.be/oP685HcFRYQ This gave me some confidence to dismantle my Nexstar 4 and clean connections in the base, as to me at least, this seemed a likely cause. But, after doing so and failing to take notes on which way connectors were orientated, I now have zero vertical slew. Everything else seems to work just fine; display and horizontal slew. I have attached a photo of the current, post clean circuit board found in the base. Ironic that I did not take a photo before detaching the connections to clean them!

 

Thank you in advance for your observations, suggestions and hopefully solutions.

 

Regards,

 

Matt

 

P.S. The two connections in question are the connection at the bottom of the image and to the right. The other large connection was lifted, cleaned and placed back how I found it.

Attached Thumbnails

  • 20190419_163748.jpg

Edited by darkmatt'r, 20 April 2019 - 02:20 AM.

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#2 mclewis1

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Posted 20 April 2019 - 11:18 AM

Welcome to CN Matt.

 

The guy that knows these GT scopes really well is George (CN username Geo), he should be able to answer any internal questions. Mike Swanson might also be along to offer some suggestions too.

 

A few general questions/comments.

 

- what are you using to power the scope?

- have you have a looked at the individual pins/sockets on the connectors you removed/replaced?

- have you had a look at the connectors at the other end (motor end)?


Edited by mclewis1, 20 April 2019 - 11:19 AM.

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#3 darkmatt'r

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Posted 20 April 2019 - 06:14 PM

Welcome to CN Matt.

 

The guy that knows these GT scopes really well is George (CN username Geo), he should be able to answer any internal questions. Mike Swanson might also be along to offer some suggestions too.

 

A few general questions/comments.

 

- what are you using to power the scope?

- have you have a looked at the individual pins/sockets on the connectors you removed/replaced?

- have you had a look at the connectors at the other end (motor end)?

Thank you Mark, I will be keepig an eye out for George and Mike!

 

You are right in singling out the power source. I had been a bit suspicious of the adaptor that came with the telescope. The jack pin that plugs into the telescope is really loose. On closer inspection the adaptor itself is non-genuine and I suspect not the right amp rating. It does not state the amps at all in fact. I would like to use a battery source, other then the AA's in the tray. I have two 20amp/h deep cycle batteries, but would need to run them through an inverter and a suitable new adaptor. Can you suggest a more affordable Lithium battery option to the Celestron power tanks?

I will have a closer more detailed look at the connections at the circuit board and the motors.

 

Thanks again Mark, I really appreciate your advice and look forward to the learning experience with the CN team in the years to come!

 

Regards,

 

Matt.



#4 mclewis1

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Posted 20 April 2019 - 09:13 PM

Matt,

 

It's important to have a stable 12v DC power source (the 12v can actually be anything between 11 and 14v) and if coming off of a mains AC supply it should be regulated and provide at least a couple of amps, more is ok too. An external battery is also a good choice and just about any 12v automotive "jump start" type of battery will work (along with the appropriate DC power cable). A lot of folks now use a small lithium battery, anything with at least 5000ma will be fine (measured at 12v not at 3.5 or 5v). If your deep cycle batteries are in reasonable condition they would be a good choice as well, and if they are 12v models there would be no need for an inverter either.

 

The power connector on the scope is a 2.1mm x 5.5mm DC power connection. Watch out for the very similar looking 2.5mm connectors which are popular on Meade products. The 2.1mm number is the diameter of the little center pin inside the socket. The mount's power is wired center positive. If you find the existing power connection is a little intermittent then have a look at that center pin, you'll notice it's a split pin and with a small blade gently pry or open the split just a little bit. This will help make a more solid connection and can also sometimes allow the wrong size (2.5mm) connector to work, but it's a really bad idea to rely on this little trick with a 2.5mm connector ... it's always better to find the correct size.


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#5 Geo.

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Posted 21 April 2019 - 11:27 AM

George here: Your plugs look oriented properly; Fairly easy not to get confused. Lower motoer is Az and its cable goes to the pins mark AZ by the stencil on the circuit board. Alt is marked as it HC for hand control. The #1 pin for each plug is indicated on the board and on the plugs themselves.

 

P1016318.JPG

 

Be sure the plug is not off register on the pins. It's easy to make this mistake.

 

 

 


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#6 darkmatt'r

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Posted 21 April 2019 - 04:44 PM

George here: Your plugs look oriented properly; Fairly easy not to get confused. Lower motoer is Az and its cable goes to the pins mark AZ by the stencil on the circuit board. Alt is marked as it HC for hand control. The #1 pin for each plug is indicated on the board and on the plugs themselves.

 

attachicon.gif P1016318.JPG

 

Be sure the plug is not off register on the pins. It's easy to make this mistake.

Gday George,

 

Thank you for jumping in and helping me with my Nexstar 4. George, are there any wiring schematics for this model available? Celestron have said no to this already, but thought I would ask anyway. I'm not qualified to actually understand the circuitry, but I do have a good friend who probably could. I am just thinking ahead if it turns out that I have a component failure, I may be able to replace them if I have a wiring diagram.

 

Regards,

 

Matt.



#7 darkmatt'r

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Posted 22 April 2019 - 01:38 AM

Matt,

 

It's important to have a stable 12v DC power source (the 12v can actually be anything between 11 and 14v) and if coming off of a mains AC supply it should be regulated and provide at least a couple of amps, more is ok too. An external battery is also a good choice and just about any 12v automotive "jump start" type of battery will work (along with the appropriate DC power cable). A lot of folks now use a small lithium battery, anything with at least 5000ma will be fine (measured at 12v not at 3.5 or 5v). If your deep cycle batteries are in reasonable condition they would be a good choice as well, and if they are 12v models there would be no need for an inverter either.

 

The power connector on the scope is a 2.1mm x 5.5mm DC power connection. Watch out for the very similar looking 2.5mm connectors which are popular on Meade products. The 2.1mm number is the diameter of the little center pin inside the socket. The mount's power is wired center positive. If you find the existing power connection is a little intermittent then have a look at that center pin, you'll notice it's a split pin and with a small blade gently pry or open the split just a little bit. This will help make a more solid connection and can also sometimes allow the wrong size (2.5mm) connector to work, but it's a really bad idea to rely on this little trick with a 2.5mm connector ... it's always better to find the correct size.

Hi Mark,

 

I came accross this power pack yesterday. Seems very good value compared to the Celestron lithium equivelent. https://www.campsmar...-centre-battery

But as I am not flushed with cash these days, I think I will be making do with my Full River AGM 20A/HR. So you don't believe I will need a regulator/inverter to run the telescope off my battery? I am happy to not spend anymore money if possible :)

 

Regards,

 

Matt



#8 mclewis1

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Posted 22 April 2019 - 08:00 AM

Matt,

 

I'm with you. Those big lithium batteries sure are nice (powerful, compact, etc.), but come with a big price tag ... and are even worse when you consider a Celestron branded product outside of North America. 

 

A 20amp/hour AGM battery would be a luxury for many folks ... and it should be fine as long as it in good condition, kept charged and so puts out a consistent 11-14v. In fact any reasonable 12v battery will work well for your scope (old wheelchair or golf cart batteries used to be very popular as long as you had a good way of keeping them charged). Today many folks are using small inexpensive off brand lithium battery packs, and they attach them to the side of the mounts so there's no issues with cord wrapping around the mount. With any of the bigger batteries just be sure you've got a good DC power cable to go from the battery to the scope (the smaller off brand lithium models often come with a suitable cable built in). Most of the time the separate DC cables have a "cigarette lighter" style plug on one end and that 2.1mm x 5.5mm connector on the other. You can find these power cables from a wide variety of vendors (it certainly doesn't have to be a Celestron branded one).

 

A good source can also be companies that carry 12v automotive supplies. You should find a variety of 12v cables and splitters. A splitter can be helpful when you need multiple 12v connections (say for powering a dew strip along with the mount) and have a nice big battery like your 20amp/hour one. DC power cables like this are also easy and inexpensive to make at home (or from someone in a local astronomy or amateur radio club), you just need to double check that you've kept the polarity correct (center pin positive).


Edited by mclewis1, 22 April 2019 - 08:00 AM.

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#9 darkmatt'r

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Posted 23 April 2019 - 09:06 PM

Gday George,

 

Thank you for jumping in and helping me with my Nexstar 4. George, are there any wiring schematics for this model available? Celestron have said no to this already, but thought I would ask anyway. I'm not qualified to actually understand the circuitry, but I do have a good friend who probably could. I am just thinking ahead if it turns out that I have a component failure, I may be able to replace them if I have a wiring diagram.

 

Regards,

 

Matt.

G'day George, PM'ed you regarding circuit boards etc for GT. Cheers, Matt.



#10 darkmatt'r

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Posted 15 May 2019 - 04:23 AM

G'day George, PM'ed you regarding circuit boards etc for GT. Cheers, Matt.

Ahoy George! Just checking in on you as I have not heard back from you with regards to a email I sent sent you. I hope you are well and when you get a chance, take a look in your message box.




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