MDM Trouble Report for 2007 Jul 17

Telescope: 2.4m
Observer(s): John Thorstensen (Dartmouth)
Instrument: Modspec + Echelle CCD

Problem(s) Encountered:
There were thunderstorms in the afternoon, so I did a lightning 
shutdown. After bringing things back up in the evening, I found
that the shutter wasn't operating (again), but this time I 
couldn't fix it by cycling power on the control box, or by any 
other simple trick I could think of.  I undid the 6 Allen screws 
holding the shutter assembly and pulled the assembly out to see
what was going on.  Commanding the shutter to open with the 
Uniblitz box caused the shutter to open partway momentarily and
then snap shut again.  I called Bob and we discussed this, and 
there was basically no way I could fix it (and it may be difficult
to fix, period, since there may not be a spare and these shutters
are no longer manufactured).  Because of this and the poor 
weather prospects, we decided to put off the fix to the morning.

I invented a workaround, also.  I left the shutter assembly
out and covered the hole in the spectrograph with duct tape --
this left the light path permanently open.  Because of this, 
when it eventually did clear later in the night, I 
was able to get exposures by obscuring the beam with the
RETROCAM prism while the chip was clearing or reading, in 
effect using this as a very slow shutter.  My exposures were
long enough that this worked very well in practice.  However,
I couldn't take comparison exposures so I had to use the 
night sky as a wavelength reference, but that's my usual
protocol when the sky is dark enough; I only lost the twilight
exposures (e.g. flux standards).

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Submitted on 2007 Jul 18 [4:56:42]