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Can't get good crystal freeze: |
check whether liquid
nitrogen dewar is empty;
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check positioning of
cooling nozzle - adjust if necessary;
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try momentarily
blocking nozzle with your thumb to build pressure, then releasing (this may
blow out ice particles that are slowing gas flow);
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get help from
MacCHESS operator (CHESS operator will contact him for you);
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Crystal icing up: |
adjust the "shield"
gas flow (regulator for red hose up at the wall) carefully between 5 and 10
L/min. Best be done with the overhead lights switched off, just the fiber
optic light on, watching the gas flow against a dark background;
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brush frost off
crystal periodically;
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come back in the
winter when the humidity is lower!?
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Return to contents |
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System does not "see" drive:
"No such device" error: |
type "scan_scsi" in
any window and try again;
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check connections of
SCSI cables, check that all SCSI devices are running;
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take tape out (if
any), turn tape drive off and on;
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get help from
MacCHESS.
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I/O errors during writing: |
take tape out, run
cleaning tape through;
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try a different tape
- "Metal" 8 mm tapes often have problems;
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if you are putting a
large amount on one tape, try splitting it up between two or three tapes.
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Return to contents |
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Completely blank image -
could be due to: |
no beam -
wait for new fill, or get CHESS operator to fix problem;
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safety
shield in front of CCD did not go up - press "garage door open" button on
the control panel, get help from MacCHESS if shield fails completely;
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software problem: |
has adxv
loaded an image? if it has, the image file name is given in the title bar,
check whether the image file is the right size;
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check display
parameters, particularly upper and lower limits for grayscale;
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for ADSC software,
check that the "ccd_xform_new_api" process is running;
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if not, restart
software with "stop_ccd" and "start_ccd"; |
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detector problem: |
check for error
messages on PC;
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|
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get help from
MacCHESS.
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Beam stop shadow visible
but no diffraction spots - could be: |
diffraction is very weak - try a longer exposure; |
| |
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|
crystal not in the beam - try rotating it 90 degrees and taking another
shot. If you see diffraction then, try to center the crystal better. If still nothing, or centering looks good but crystal only
diffracts at some positions, could be a problem with video camera
cross-hairs or spindle height - get MacCHESS help to fix;
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crystal is no good (sorry!) - try another.
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Oscillation image looks
like a still: |
check the oscillation range that you entered;
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get CHESS operator to check spindle motor.
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Shadows on image: |
check for cooling nozzle too close;
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other equipment blocking part of the X-rays.
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Areas of high background
on image: |
check position of beam stop, adjust if necessary;
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beam
stop is too small, move it forward or get operator to put on a bigger one;
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have CHESS operator add shielding.
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Strong discrete spots or
rings on image - could be due to: |
ice or salt in or around crystal - change crystal; |
| |
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|
if problem persists with a
new crystal, is probably
due to one of the following:
|
crooked
collimator ion chamber - straighten it; |
| |
|
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|
particles of dust, etc. in collimator - blow out collimator with air;
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switch
to another collimator.
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Return to contents |
