Telescope Focus Failure

Wednesday, February 28, 2018 10:38 AM

Problem(s) Encountered:

When I set on a bright star in twilight I found I could not focus the telescope with either the hand paddle or the gui - the focus number would not move and the image would not change.

Damon Burke of DFM had been working on the program during the afternoon, so I figured it was something he did.  I called DFM in hopes he''d be there, and got Frank Melsheimer himself on the phone, who passed the message on to Damon; Damon then logged on remotely and tried to diagnose the problem.  He concluded that the focus motor was spinning, but the encoder was not seeing any change, so we inferred that something in the mechanism has failed (perhaps a drive belt).  I observed the rest of the night with the telescope out of focus, losing most of the light on the slit jaws.


At the start of diagnosing the problem, I verified that focus was not moving.  I then set up the telescope to allow access to the secondary mirror (M2) system.  In order to get a hand paddle up to the M2, I used the ‘focus only’ hand paddle that was acquired by UM.  Tinkering, the focus started working again.  While running through focus, I tested the in/out limit switches and found the ‘in’ switch to be intermittent at best.  Also, during this, focus motion stopped yet again.  I switched out the bad limit switch but still no movement.  Verified power to the motor and that the focus travel was smooth by hand.  All seemed ok.  At this point, Damon contacted me and had me plug the motor back in for tests from his end.  And lo and behold, it worked.  He transferred power back over to our end and I was once again able to move the motor.  Put everything back together and all still works.  Not really sure what was wrong.  Symptoms seem to defy all logic.  According to Damon, last night he was able to verify that the motor was indeed turning, but focus was not changing.  This pointed to a broken belt in the drive  But the belt was fine.  Then today, the problem for me was that the motor was not turning.  But then it was.  Then it wasn’t.  Then it was again.  I just don’t know.  But it is working.  And perhaps something we did has something to do with that?

Sorry if this isn’t the most satisfying trouble report response, but I’m baffled, tired and ready to head home.