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Upgrade of a NexStar 5/8 (1999) to NexStar 6/8 SE Electronics

Celestron DIY Mount
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#1 SieglindeFestkochend



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Posted 03 September 2022 - 07:34 AM

The following instruction is about upgrading the electronics of a NexStar 5 / 8 from 1999 (gray) to the electronics of a NexStar 6/8 SE.



The upgrade enables:


• Operation of the newer hand controllers
• AUX port
• guiding port
• Remote control by a computer (or a smartphone with additional extensions)
• Use of WLAN and GPS interfaces
• Skyalign


In its original state, the NexStar 5 / 8 can only be operated with the hand controller, which corresponds to the version smaller than 4. These old hand controllers cannot update via the Celestron firmware manager an they are out of stock.

The conversion can be performed on both NexStars from 1999: NexStar 5 and NexStar 8, because the mount is identical.


Here is a warning: I assume no liability for any damage that occurs during DIY.


The reason to research this conversion was originally not modernization. The hand controller was defective. The NexStar from 1999 can only be operated with the old handcontroller and exactly this hand controller is no longer available. Therefore the idea was to get a new motorboard, so that the telescope can be used again with the new handcontroller.
What I knew for sure, as the info comes from Michael Swanson, was the compatibility with the NXW-200 motor board from the NexStar 5i. This board was unfortunately also no longer available, neither used or new. So: Is this a dead end with no turning point?


After I had almost given up on the project, I found a post by MikeStar in CloudyNights: "Upgrade of 8i SE Aux/MC boards to newer SE"


This is about an upgrade of a NexStar 5i telescope with the original NXW-200 board to the newer NXW-437 board. So my NexStar 5 (1999), where the NXW-200 also works, should be upgraded with a NXW-437. This newer board is available (at Baader Planetarium for example) and the corresponding AUX board as well (NEX6-F00-5). This modern combination is much cheaper than a NXW-200 (if you can find it, it is priced around 350$).


The needed parts are:

• NXW-437 Motorboard  ca. 115€
• NEX6F00-5 Aux-board  ca. 35€
• Various cables and connectors ca. 20€
• Soldering iron, heat shrink tubing, various small tools (cutter, screwdriver...)


The adventure can start: Disconnect the power supply!


It is imperative that the power connection is not made during the first operations. The battery compartment should be emptied, as it is easy to forget the current supply via the batteries. I do not describe here how to disassemble the OTA and the housing. There are some instructions for this.
I have not been able to remove the cover with the battery case without first disassembling the OTA. Research has shown that this is the case with the NexStar 5 / 8 from 1999 this is the case. Allen wrenches in inches are needed.


In contrast to the procedure of MikeStar, from the forum CloudyNights, I wanted to not to adapt the blue connectors of the 1999 telescope to the new connectors of the NXW-437 (with a cutter for example). As connecting cable between the motor board and the AUX board (interconnection) you have to get new connectors in standard JST-XH, consequently the connections to the motors, encoders, power supply and handcontroller can also be changed, encoders, power supply and hand controller can be adapted. The new connectors are:


- JST XH in 6-pole: 7 pieces
- JST XH in 4-pole: 1 piece
- JST XH in 2-pole: 3 pieces


First of all, note the pin assignment of the blue plugs as a check. This makes it easier to revert to the old state, if you should decide differently in the course. The cables in the blue connectors are crimped, I pulled the cables out of the no longer needed blue connectors, removed 5 mm of insulation and already tinned.


The new connectors are also an advantage because the power supply of the board has to be organized a little bit different. I got the JST connectors with already attached cables and open ends, because I can connect them with soldering iron and shrink tubing to the cables of the NexStar 5. Do not forget: First pull the heat shrink tubing over one cable end and then solder....

Soldering experience is required, but only cable ends need to be connected. No soldering of connections is required or changed on the boards themselves, because edge connectors are used.


Explanation of terms for the encoders, for understanding


The motors for AZM and ALT are equipped with components that report the exact position and speed of the motor shaft to the electronics of the motor board. On the shaft sits a segment wheel (slotted disc) which is illuminated by a light source. Opposite the light source is a photodiode, which either receives light (through the slit of the disk) or not, because the path is interrupted. The signals of the photodiode are transmitted to the electronics and counted, also the direction of rotation is evaluated.
The encoders receive 5 V operating voltage from the motor board via a cable and then a line for the ground. The signals are transmitted via two other lines, so the encoders have 4 lines.

The type of the encoders is HEDS 9100 F or in the notation HEDS-9100#F00. The encoders are replaceable, if an encoder should be defective, you can get it at ebay for about 25 EURO.


1. Cables of the motors and the associated ALT and AZM encoders


1. A: Connect the cables of the motors to the new connectors:


The motors of the NexStar 5 are each equipped with two cables: One two-pole for the drive of the motor and a four-pole one for the encoder.
The photo shows, coming from the motor (top), the cable for a drive (black as PIN 1 and red as PIN 2) and on the right the cable with power supply and the signals of the encoders.


1 A.jpg


These four PIN's are black, red (PIN3 and PIN 4, ground and power for the encoder) green and yellow (PIN 5 and PIN 6, signals encoder) on the original cables. Here you can see the shrink sleeves, which protect and isolate the solder joints of the points of the connection.


The order of the PIN's is crucial. One can see: All three wire pairs are crossed!


Please note: The color scheme of the new cables of the JST-HX connectors may be completely different from the on the photos that can be seen here. Therefor please note only the designation of the pins (from 1 to 6). I do not refer here to the colors of the new cable, but to the order of the pins from left to right.


1. B: Connector of the motors and its encoder on the board


Here you can see the connector for the ALT motor at J2 and J6 on the NXW-437 board. Again starting from the left PIN 1 to PIN 6. Do exactly the same for the AZM motor.


1 B.jpg


All three wire pairs are crossed:


PIN 1 of the motor cable goes to PIN 2 of the board
PIN 2 of the motor cable goes to PIN 1 of the board.

PIN 3 of the motor cable goes to PIN 4 of the board.
PIN 4 of the motor cable goes to PIN 3 of the board

PIN 5 of the motor cable goes to PIN 6 of the board
PIN 6 of the motor cable goes to PIN 5 of the board


If you mix up the PIN's, the motor always runs at the highest speed, not controllable by entering the speed on the hand controller. If this behaviour of the motor occurs, then this is the error. PIN 3 and PIN4 mixed up can destroy the encoder. A test run should be made before reassembling the telescope. The test run can be done on the fly, i.e. with the two boards on the work table. However, we are not yet there.



2. Power supply via AC adapter and batteries


• The power supply must be reorganized.


2. A: Battery compartment cable: Remove batteries!


2 A.jpg


The photo shows the left side AUX board. The red arrow shows the PIN's of the power supply with batteries. The designation of the socket is J2 BAT, left plus and right ground. Here the cables according to the colors red and black can be connected with a solder joint and heat shrink tubing to the battery compartment.


Do not yet insert batteries!


A two-pin JST-XH connector is required here.


2. B: Cable of the socket for the power supply and for the main switch.


I decided that the first step would be to remove all of the existing cables of the power supply, because the original used round plugs have very bad characteristics and the switch is connected differently than on the original board.

The AUX board has four PIN's on the J7 POW (red arrow in the photo): Two for the power supply via the power supply unit and two for the main switch. I use again a JST-XH connector, here with four poles.

Two PIN's are electrically connected through on the board,
from the left: PIN 1 and PIN 3. PIN 1 is plus from the power supply, PIN 2 is its ground. PIN 3 goes to the switch and PIN 4 from the switch back again. The switch feeds the current coming from pin 3 further into PIN 4, when the switch is in the ON position.


2 B.jpg

The central connection of the 12 Volt socket (left in the picture) is the positive pole (red) of the power supply, the outer connection is ground (negative pole in black).

For the switch I decided for this connection, shown on the photo, left white and right yellow. The power supply is ready then.


2 B 2.jpg


see next post...

Edited by SieglindeFestkochend, 04 September 2022 - 05:47 AM.

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#2 SieglindeFestkochend



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Posted 03 September 2022 - 07:47 AM

3. Connection of the socket in the storage compartment of the hand controller to the AUX board


• The six-pole cable, which comes from the socket in the storage compartment is connected internally with a connector to the original circuit board with a different plug and connected to the AUX board.


3. A: Cut the cable of the hand controller close to the connector.


The photo shows (red arrow) the connector J4 HC at the AUX board with six wires. Before the socket of the hand controller was connected from the storage compartment with an extension cable to an inaccessible socket of the motor board. This socket sometimes suffers from contact problems, because it is not accessible under the cover of the mount and therefore is not unplugged and plugged in again. This problem is now eliminated.

The internal cable of the hand controller is now connected directly to the AUX board with a soldered connection.

From left to right you can see PIN 1 to PIN 6 of the connector.


3 A.jpg


3. B: Solder connections of the cable for the hand controller to the connector J4 of the AUX board


Cable of the hand controller from left to right PIN1 to PIN6.


3 B.jpg




No wires need to be crossed.


PIN1 to PIN1
PIN2 to PIN2
PIN3 to PIN3
PIN4 to PIN4
PIN5 to PIN5
PIN6 to PIN6


4. Connection between motor board and AUX board


• Two six-pole cables connect the boards


4. A: Connector on the Aux board


Here two cable connections with 6 poles each are made, which connect the boards motor board and AUX board: Socket J1 AG and socket J3 MC is the designation on the AUX board, as shown in the photo.
In each case again from left to right PIN1 to PIN6. The wires can each be connected to the same colors or designations of the connector at the other end. No wires are crossed. I have used pre-assembled connectors with cable ends with soldered connections and heat shrink tubing to cables with one plug at each end. Maybe there are also ready-made cables with a plug at both ends, i have not found them.


4 A.jpg


4. B: 2 connectors on the motor board


4 B.jpg


Here you can see the connectors on the motor board. The designation is the same for the AG J2 (autoguiding) and is connected with the counterpart AG (here J1) on the AUX board.
The connector on the motor board with the designation SBB J1 is connected to the MC connector on the AUX board.
It is useful to assign a color code to the connectors to avoid confusion later on.


5. Third connection between the motor board and AUX-board



On the AUX board (photo) is a socket with 2 poles can be seen (J8 INDEX). PIN 1 goes to PIN 1 of the socket on the motor board with the designation J7.


5 A.jpg


With this connection, according to my research, the power supply from the AUX board to the motor board. Directly at the socket of the motor board sits the voltage regulator for 12 V and 5 V (photo).


5 B.jpg


see next post...

Edited by SieglindeFestkochend, 04 September 2022 - 05:53 AM.

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#3 SieglindeFestkochend



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Posted 03 September 2022 - 08:04 AM

6. Function test before mechanical assembly


• Check and think through all connections again.

When all connections have passed the second check, either the battery compartment or the power supply unit can be connected. The hand controller can also be connected to the AUX socket on the board, or is already connected to the socket in the storage compartment. After the base has been switched on, the hand controller should be illuminated and the display should first show the following display:


• for a few seconds: "Verifying Packages Please wait".
• for a few seconds: "Scanning Please wait".
• then: "NexStar SE" with a request to start the alignment, which we do not do.


Function test with "flying" electronics on the workbench:


• first operate the direction keys and check the function, this still in Speed 9 (i.e. without change). Left arrow key turns the telescope counterclockwise. Arrow up key rotates the OTA in the direction of the zenith (base arm left). This can be checked via the gear wheel, which turns the ALT (OTA).

• Select speed 7 via the "Motor Speed" key, i.e. first press the key "Motor Speed" and then immediately press the key 7. Again check the function with the direction keys and check if the speed of the motors is lower. This can also be determined by the motor noise, which should be much quieter.


If this function test is positive: Congratulations, you can proceed to the next item!

If not, then the manual must be gone through again, depending on which motor is affected: ALT or AZM.


The next test I have found in a manual from Celestron.


Here a DIY - upgrade was offered, the exchange of a circuit board, and a function test was suggested. Here is an image of this function check: The undo button cannot be pressed, there is no such key, it does not exist on the new hand controller. One presses "Menu" and navigate to the "Utilities", select them and further down you will find the item "Show Alt/Az". It can be checked, if the direction of the motors is correct in the set speed 9. In the default setting the direction of action is reversed in the low settings, therefore the test is performed in speed 9.




• If the right direction key is pressed, the value for the Az coordinates must become larger and vice versa.

• When the upper direction key is pressed, the value for the Alt coordinates must become larger and vice versa.


If everything fits, switch off the telescope, cut the power supply again and reassemble the telescope as suggested in the next section.



7. Mechanics:


7. A: Changes to the cover of the battery compartment and mount



The original NexStar 5/8 does not have any connection at the top of the base. With the new AUX board two sockets are added: AUX and Guide (autoguiding). There must be two rectangular openings in the plastic cover of the of the base. I used a cutter with some patience and a metal rail as a guide. Before that, the corner points of the openings have to be defined. It is advisable to fix the corner points with a drill hole. I do not give dimensions, this must be measured and transferred. Here comes the cover of the battery compartment (which also gets openings) over these openings, therefore this operation does not require high precision.


7 A 1.jpg


This next photo shows you three holes around the new bushings. These are the points to mount the AUX board to the cover of the base. The holes are a bit countersunk and I used countersunk screws, so that the screws do not protrude (lower photo on the left side).


7 A 2.jpg



The openings of the lid are transferred to the lid of the battery compartment and the corners are again defined with holes.


With the openings in the lid of the battery compartment it is worth working accurately, the edges of the square openings are visible.



7. B: Attachment of the AUX board to the cover


The original NexStar 5/8 1999 has a large circuit board in the base, on which all functions are combined. The rebuilt NexStar now has two boards, motor board and AUX board. In the NexStar SE these two boards are arranged one above the other, attached to a bridge made of metal. I did not find this bridge on the market and therefore decided to mount the AUX board directly under the cover of the base. In the photos in the upper section you can see the three screws. Here you can see the AUX board seen from below with the three nuts to fix it to the lid. Sleeves must be used as spacers on the three screws, so that the AUX board is not under mechanical tension. I have deliberately left the connecting cables between the two boards longer, so that you can still handle the lid when the cables are plugged in.


7 B.jpg



7. C: Fastening the motor board to the base


I have removed all the plastic dowels in the base. Now the motor board has to be mounted on the base. I used a metal rail and screwed this rail to the base at two points. The metal rail gets two holes before, to be able to fix the motor board here. Again plastic spacers (sleeves) must be used, so that the backside of the board cannot touch the rail and thus prevent short circuits.


7 C.jpg


Perhaps there is a more elegant way to attach the boards to the mount. This solution, however, works very well. The longer connection cables can be sorted a bit with cable ties before assembling. The lid of the base can now be removed without having to disassemble the OTA first. So, now assemble the base, fix the cover of the arm of the mount...and mount the OTA again.


For mounting the tube there are again instructions in the CloudyNights. One must be careful not to overtighten the nut of the axis. The slipping clutch of the tube must still be effective, i.e. it must be possible to turn the tube in the AZM direction by hand against resistance.


see next post...

Edited by SieglindeFestkochend, 04 September 2022 - 05:41 AM.

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#4 SieglindeFestkochend



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Posted 03 September 2022 - 08:15 AM

8. Last check of function





9. Mount the cover of the base






Many thanks for the support in the Forum CloudyNights, especially MikeStar, without whose idea my NexStar would have become a paperweight.

I would also like to thank CharLakeAstro and Michael_Swanson. Thanks also to Baader Planetarium for the translation into English.


If there are any errors in these instructions, please send a message to my account in the CloudyNights: SieglindeFestkochend


Have fun with your upgrade! The telescope works perfectly, here in Husum (Germany) were some wonderful nights with a very good seeing.


I would like to write a better formatted article from this guide or offer a PDF for download. I haven't received a response from submit@cloudynights.com yet

Edited by SieglindeFestkochend, 04 September 2022 - 05:42 AM.

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