Guider Focus Motion Failure(?)

Friday, September 1, 2017 1:17 PM

Problem(s) Encountered:

Spent about 10 minutes trying to focus the guider camera before realizing that I can''t move it either way.  Don''t bother about this; it still guides okay on a donut.


Checked the voltages on the KMTronic USB Relay box used to gate voltages to the guide probe motor mic.  Voltages are as expected (±12Vdc).  Pulled the detector and FW and opened access hatches.  Verified that the motor mic moves in and out as commanded via focus GUI (on guider PC).  Then verified that the mechanics attached to the motor mic are also moving by placing my finger in front of the stage that the prism sits on and feeling the stage move in/out as focus in/out demands are made.  Not sure what else could be going on to cause any issue as everything appears to be working.  I did go ahead and move the rough position of the motor mic inwards a bit as I noticed that the motor mic was biased inwards.  I then moved the fine focus outwards a bit to compensate.  

Since the guider is robust enough to guide on an out-of-focus image, I think all that is left to try is to go back on-sky and see what things look like.  Since the telescope is not scheduled for tonight, perhaps I can try running from home if time/weather permits.  Otherwise, the current state of the system can be verified tomorrow night by the Gallo crew.

Incidentally, it should also be reported that when pulling the FW and installing it again, I ran into issues with 2 helicoils.  The one east-of-center on the north end pulled out completely.  This is not too much of an issue as the bolt hole is a pass-through.  So I have simply utilized a longer bolt and a nut.  

The second one is more concerning.  It is east-of-center on the south end.  It is holding, but I cannot tighten it completely as the bolt will then loosen again.  So I can only tighten it to the ‘sweet spot’ where I feel the most tension on the bolt. The truly concerning part of this one is that the south-of-center helicoil on the east side has already failed badly enough that it is questionable whether or not a new one can be installed.  If we lose both helicoils on this corner, there would be no bolts to support the SE corner of the FW.  

It is certainly time to consider how to resolve the helicoil issue on this FW, and possibly time to consider fabricating a new top-plate for this FW.