From: Bob Kibrick
To: Greg Wirth
Subject: an alternate proposal for unswapping the CCD 1A & 1B videos
Date: Tue, 19 Aug 2003 11:33:06 -0700 (PDT)

Greg and Hector,

I have looked at the results of Greg's IDL test script that ran last night.
Unfortunately, after 375 exposures, we failed to see even a single case of
the intermittent dropout problem from CCD 1A/1B.   I'm running additional
tests this morning in which I'm alternated between spectral/single:b 
readouts and direct/dual:a+b readouts, and I have yet to see a single
recurrence of the intermittent problem.

Either we are just unlucky (e.g., the "watched water never boils" syndrome),
or we may have inadvertenty "fixed" the problem by messing with the SMA/SMB
connectors that pass the video signals into the front of the video processing
board.  (These are the most delicate connectors on the portion of the
electronics that is external to the dewar and its dewar electronics.)

If  the latter is the case, then we might potentially re-introduce the
problem if we swap these video cables and their delicate SMA/SMB
connectors back to their original configuration.

Instead, I propose that we swap the CCD 1A and 1B video signal coaxes at
their respective BNC connectors on the BACK panel of the DEIMOS science
mosaic controller (the back panel faces toward the telescope).  The back
panel is easier to get to, and the BNC connectors are much easier to
remove and re-attach.  

The wiring would then look like this:


  Dewar                Preamplifier            Preamplifier
  Electronics	       Output for              Output for 
  Box		       CCD 1A amp              CCD 1B amp
                            ^                       ^
                             \BNC               BNC/
                              \                   /
                               \                 /
                                \               /
                                 \             /
                                  \           /
                                   \         /
                                    \       /
                                     \     /
                                      \   /
                                       \ /
                                        \
                                       / \
                                      /   \
                                     /     \
                                    /       \
                                   /         \
                                  /           \
                                 /             \
                                /               \
                               /                 \
                              /                   \
                             /    Swap these two   \
                         BNC/    cable ends today   \BNC
                           V                         V
  Back Panel          CCD 1A amp                CCD 1B amp
  BNC Connectors           ^                         ^
                            \                       /
                             \                     /
                              \                   /
                               \                 /
                                \               /
                                 \             /
                                  \           /
                                   \         /
                                    \       /
                                     \     /
                                      \   /
                                       \ /
                                       / \
                                      /   \
                                     /     \
                                    /       \
                                   /         \
                                  /           \
                                 /             \
                                /               \
                               /                 \
                              /                   \
                             /                     \
                         SMA/                       \SMA
                           V                         V
  SMA/SMB             CCD 1A amp                CCD 1B amp
  Connectors
  on front of              The cables to these two connectors
  Video Board              were the ones swapped on August 5, 2003.
  For CCD 1		   Leave these alone.


If we agree to proceed with this plan, then I suggest we print a copy of
this e-mail (or make a reduced copy of it) and prominently affix it to 
the side of the DEIMOS science CCD controller so that techs will understand
why the wiring/labelling was perverted in this manner.  We should also
commit a copy of the text of this e-mail to a documentation file that is
checked into the document directory of the DEIMOS CVS repository.

Regards,

Bob

P.S. If we do this, my apologies to Steve Allen, as it will completely
     mess up his very nice drawings of this cabling.