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No Response Errors

Please read this entire article before you start troubleshooting.

You may also want to read the article Internal Communications of Celestron Computerized Telescope Mounts before you start.

This error indicates that the hand control is unable to communicate with another system component, for example, 16 and 17 are the motor control processors located inside the mount.  176 is the GPS module on scopes with this option.  178 is the Real Time Clock (RTC) module on scopes with an RTC.

All Models
A common source for this error is faulty power, either low voltage (weak batteries or AC adapter) or a loose connector.  Read this for suggestions regarding power.

Many times the problem is the connector that the hand control plugs in to.  Try connecting the hand control to one of the AUX jacks (for mounts with an AUX jack), rather than the normal hand control jack.  Also, the pins on the jack or the plug can accumulate slight amounts of corrosion that can interrupt the low voltage signals.  These can be easily cleaned with contact cleaner available at electronics parts stores. Do not over do it, you do not want excess cleaner to short out the electrical connections.  Be sure the power is off and use a cotton swab dampened with contact cleaner to rub any contaminants from the connectors. Also, take a good look at the pins and insure they are not bent or misaligned.

Another potential problem area is that the plastic RJ-12 connector (phone-type connector) on the end of the coiled cable might need to be re-crimped or replaced.  Or, occasionally the connection of the coiled cable inside the hand control has worked loose and causes No Response errors.  This can be fixed by carefully removing the back of the hand control (6 screws hold it on) and reseating the connector. 

Occasionally one of the modules connected either to the AUX ports or the internal communication bus (the AUX bus) is bad and is flooding the communication bus with garbage thus preventing the hand control from communicating.  For example, this has been seen with the internal GPS module on a CPC scope.  Opening the base and disconnecting the GPS module allowed the hand control to communicate with the motor control in the mount and by manually entering date and time, the scope was again operational.  Bad external modules like an external GPS unit, a SkyPortal WiFi module or a StarSense camera could also cause this type problem - test by disconnecting everything except for the hand control and power (the minimum required to use the scope).

On rare occasions, the motor control may be stuck in "boot mode".  Fixing the problem requires you reload the latest motor control firmware - follow these instructions.

NexStar Evolution Series
On the Evolution mount, you can sometimes fix No Response errors by pressing the reset button located below the two AUX ports on the side of the fork arm.

NexStar GPS Series
If you receive a "No Response 1" error when checking version on a NexStar 8/9.25/11 GPS, this is not a problem.  This is caused by a new version of the serial board inside the mount.  The old version responded to version requests while this new version does not.  So, a "No Response 1" error is nothing to be alarmed about and can be considered "normal" behavior.

The newest versions of the hand control - version 4 or higher - require motor control firmware version 4 or higher.  If you have older motor control firmware, the hand control will display the no response error.  See this article for details on GPS firmware versions and upgrading when necessary.

Advanced Series with GoTo (AS-GT)
There is a problem on some AS-GT mounts regarding insulation between the bottom of the motor control board and the mount.  Peter Bruce has written an article describing the problem and the fix.  Click here to download the article.

Internal Connections - All Models
If none of the above resolved the issue, there may be a faulty connection inside the base.

NexStar GPS Series
For the NexStar 8/9.25/11 GPS, start by disconnecting the power from the telescope.  Using a 3/16 inch hex wrench, remove the two bolts securing the handle to the left fork arm.  Using a 9/64 inch or 3.5mm hex wrench, remove the plastic covering on the left fork arm.  Remove and reseat all connector cables attached to the small motor control circuit board - this usually wipes off any accumulated corrosion or re-establishes lost connections.  Be very careful not to misalign the pins and the connectors or damage may result.  Replace the cover and the handle and test the telescope.

If you still experience problems, there may be a connector loose under the panel on the base of the scope. Using a 9/64 inch or 3.5mm hex wrench, remove the five bolts on the top of the base panel. In a well-lit space, slowly raise the panel, being careful not to pull any of the cables loose. With the panel raised about 2 inches (rolled-up socks are a good way to prop it up), reseat all connector cables you can easily reach. Reseat the panel and secure the five bolts.

NexStar 5i/8i/8i Special Edition and NexStar SE Series
For the NexStar 5i/8i/8i Special Edition and the SE series, open the battery cover and remove the four screws securing the base cover.  Carefully lift the base cover, noting there is a cable running from the battery holder to the base.  You may find on your scope that you also need to loosen or remove the two lower screws on the plastic cover on the inside of the fork arm.  After removing the base cover, remove and reseat all connector cables attached to the circuit boards.  Be very careful not to misalign the pins and the connectors or damage may result.  Replace the cover and test the telescope.  On some scopes it may even be necessary to remove the optical tube and then completely remove the cover on the inside of the fork arm.  This is not a terribly difficult task - but harder to explain in a single paragraph.  I did cover it in the Maintenance chapter of the first edition of the NexStar User's Guide and these two articles (azimuth axis and altitude axis) will help.

NexStar GT, NexStar SLT, Astro Fi, SkyProdigy Series
Open the fork arm (remove the plastic outer cover) and remove and reseat all connector cables attached to the circuit boards.  Be very careful not to misalign the pins and the connectors or permanent damage to the circuitry may result.  Replace the cover and test the telescope.

All Other Models
Similar procedures might fix this problem on the CPC, LCM, CGE, CGE Pro, CGEM and Advanced Series with GoTo (AS-GT) models as well, be sure to use caution when removing and reseating cables to ensure you do not misalign the pins.  Permanent damage can occur.


If none of these suggestions helps, it is time to try replacing hand control, circuit boards or cable assembles. Or it is time to call Celestron.

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Michael Swanson
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