This afternoon I fixed a fault with the Paramount ME myself.

Just a few weeks after I started to run the Paramount ME I hit trouble – the mount would not home in declination properly.  When I hit “home”, the declination axis would move in a clockwise direction, go past the “home” position, and would have hit the mechanical stop if I hadn’t aborted the “home” procedure.  By trial and error I found that I could get the mount to “home” in declination if I started off with the mount in its maximum anti-clockwise position hard up against the stop.  Occasionally it would not home properly even if I did this and I would have to rotate the mount back and try several times.

I worked with the mount in this way for maybe 8-12 months until one clear night when I went out to image and it just wouldn’t home in declination at all.  Very fed up I came back indoors and lost a perfect night’s imaging.

The next morning I took the declination sensor assembly out of the Paramount ME (this in itself was a HELLUVA job!) and cleaned the optical path.  After I put the sensor back the homing worked perfectly with the declination axis in any position (as it should) and I felt I had found the problem.  Unfortunately within a week or so it started playing up again and I had to hard rotate the declination axis anti-clockwise for it to find declination “home”.  That was until last week when it just stopped finding “home” again – for the second time.

Knowing that the cable looked fine I assumed that the problem was with the sensor and contacted Software Bisque.  Software Bisque immediately sent me a replacement sensor which arrived today.  Full of anticipation I opened the package to find they had sent me the wrong sensor.  The declination sensor in the Paramount ME has two side lugs where it is screwed to the metal sensor mount assembly – the sensor they sent me had no lugs.  I e-mailed Software Bisque to tell them that they had sent me the wrong sensor (I assumed that they had sent me the RA sensor instead of the DEC sensor) and they wrote back telling me that both sensors are the same on the Paramount ME.  I then wrote back that in that case they had sent me the wrong sensor entirely as it had no side lugs as the declination sensor has and this was shown in the photo that I also e-mailed them.  I have not yet heard back from Software Bisque on this issue.

As you might imagine, at this point I am very annoyed and very frustrated, so I go out to the observatory and remove the sensor completely from the Paramount ME, the idea being to see the make and type and order an equivalent from RS.  However, before ordering from RS I had a nagging feeling that I should check the connection of the wires to the pins on the sensor.  Where the wires are attached to the 4 sensor pins there is some yellow shrink fit insulator which needs to be removed to check the join.  I took the shrink fit insulator off using a Stanley knife and was amazed at what I found.

The pins of the sensor had been made into loops (fine), the bare end of the wire had been threaded through the hoop (also fine) and then turned back on itself (fine again).  There had been some sort of attempt at soldering, but there was so little solder on the joint that ALL FOUR WIRES COULD MOVE FREELY AROUND INSIDE THE PIN LOOPS!!!!  Yes you did read that right, effectively the wires were not electrically connected to the sensor pins at all – the only connection was where they fortunately touched.  It was amazing that the mount ever worked properly at all.

Now knowing what the problem was, I soldered the 4 wires to the pins on the sensor and re-assembled the whole thing.  Fired up the Sky 6 and “homed” the mount via the computer.  The mount went directly to “home” with no problem at all, and I hadn’t set the declination axis off at its maximum anti-clockwise position either, I set it off with the scopes facing north.

I have e-mailed Software Bisque with my findings and the recommendation that they carefully check with whoever does the sensor assembly that they correct procedures are being followed.  I am awaiting a reply.

By the way – in case you haven’t worked it out for yourself – why did moving the declination axis hard anti-clockwise sometimes make the “home” procedure work?  It was because at the limits of its movement the cable connecting to the declination sensor to the main board would be strained sufficiently for it to pull on the sensor pins and thus create an electrical connection.  That’s why it was so intermittent.

STOP PRESS:  I have just received an e-mail from Software Bisque.  They apologise for sending the wrong sensor and they will be checking on the manufacturer who puts the sensor assemblies together.  Well that makes all the hours I wasted on sorting this one out all worthwhile then.





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