I have tried to reload the firmware ( CFM ) a few times but it does not fix the problem. As stated earlier a second HC works perfectly so the problem lies in the HC. Still under warranty so I may ask Celestron for a new HC. Running out of ideas to try.
Does Mike Swanson have any ideas?????
I have his book and did check out his nexstar site.
Sorry, been really busy lately and haven't had time to read all the posts.
As noted by others and yourself, since a second HC works fine, the problem is in the HC. If you contact Celestron I'm fairly certain they will send you a new HC. As far as what might have gone wrong, since the hand control powers up and basically functions normally, that means it is getting power from the mount. Thus, the +12V and ground pin in the RJ-12 plug are fine. But, the transmit and receive pins are having issues. There are just a few possible failure points.
First, the clear plastic RJ-12 plug may have issues. The only sensible way to fix that is to cut it off and crimp on a new one. You would need the appropriate crimping tool, a new RJ-12 plug and you must be certain you insert the coiled cable in the same orientation (notice the wire colors) as the original plug.
Second, the connector where the coiled cable plugs into the circuit board inside the HC might need to be cleaned and/or reseated. You would need to remove the back cover to get to that.
Third, the coiled cable may be damaged. This is least likely unless you see obvious physical damage.
And finally, the electronics in the communication buffer for either transmit or receive have failed. No easy fix there as that involves replacing tiny surface mounted electronic components. The buffer circuits can simply fail due to faulty components but everyone should be aware you can also damage them by plugging or unplugging the hand control while the mount is powered on. What happens is the ground pin is disconnected momentarily while the +12V pin is still connected and the 12V power finds its way to ground via the transmit or receive pin, damaging the buffer (those circuits are designed for 5V). This is rare, but it does happen.