GRIM II's single 256 x 256 NICMOS 3 chip is read out simultaneously with four amplifiers, dividing the array into four quadrants, or "quads", which can be considered semi-independently. For several years, the generally reliable character of GRIM has been intermittently (and randomly) punctuated with instances where one or more of the readout quadrants fails to read out properly. The symptoms are either quads that return inappropriate signal levels, or none at all, while adjacent quads function normally. The unpredictable quality of this problem meant that the instrument would function with all four quads operating reliably for weeks or months, then in one night we could potentially lose an hour or more trying to recover when a quad would drop. After some black magic, said quad would return and GRIM would work reliably for the remainder of a night. In November 2003 we saw the frequency of the occurrence of this problem spike, to the extent that quadrants were dropped in nearly every image GRIM returned. At that point, GRIM was taken out of service while we attempted to find a fix to the problem. Dale Sanford (UC), one of GRIM's original architects, was brought in during December to evaluate GRIM's condition and to assess the nature of the problem. During his stay, the exterior (i.e., outside the dewar) electronics were tested for obvious faults, and we characterized the performance of what at the time were the still reliably functioning quads. Dale concluded that the root of the problem lies within the dewar. Although another annoying problem may be corrected with improved ventilation. This ventilation modification will be completed within the next week or so. Any further repair work would require opening the dewar. An undertaking that will be very time consuming and with risks as there are a number of other repair and maintenance items that would have to be addressed once the dewar is opened. Concurrently, the University of Colorado-built Near Infrared Camera/Fabry-Perot Spectrometer (NIC-FPS) is scheduled for completion and commissioning in mid-'04, with routine science operations to begin around the first of the new year. The point of this message is to address how ARC near-IR programs will be affected for the remainder of 2004. As of January 2004, GRIM exists in a semi-functional state. Our characterization of the three quadrants that were "alive" in December indicates that the presence of a bad quad doesn't appear to affect the adjacent quads. We verified quantities such as gain, read noise, linearity and dark current and found those values reasonably close to the ones tabulated on the APO website http://galileo.apo.nmsu.edu/~jcb/apo/grim/ One somewhat consistent aspect of the problem is *which* quads tend to drop; i.e., the leftmost two quads, as viewed in IRAF, seem consistently alive, while the upper right quad is most flaky and the lower right quad somewhere in between. The main impact of this problem on science programs is, again, the unpredictability of the quadrants. On a given night, all four may be functional all night, one or two may drop either periodically or permanently through a night, or some permutation of these possibilities may exist. Non-scripted, pointed observations would not suffer unreasonably from this effect, but considering that most GRIM observations are scripted, the current state of GRIM has a definite and significant impact on the majority of GRIM science. Observers considering proposing GRIM observations later in the year should consider these issues carefully. Most importantly, all potential 2004 GRIM users should be prepared for the circumstance that GRIM may be taken out of service either temporarily or permanently, at any time and for any length of time, before NIC-FPS becomes available. The engineers at APO hope to keep GRIM running long enough to overlap with early NIC-FPS service and to characterize the new instrument sufficiently to allow for correlation of its data with GRIM data, determination of zeropoint shifts, etc. But this calendar year will be very tentative with respect to near-IR data and the 3.5m telescope. Users should plan accordingly. Also, any planned outages for service and repair will be announced to the community as far in advance as possible to keep the chaos to a minimum. Observers faced with using GRIM in its current state should be on the lookout for dropping quads during their observations, but there is no evident cause to mistrust data the other functional quads are giving. If a functional quad drops during the night, be sure to let your Observing Specialist know. Any other unusual artifacts in the images or otherwise odd behavior should also be noted immediately. John Barentine/Mark Klaene/Ed Turner -- Mark Klaene Deputy Site Manager voice: 505 437 6822 PO Box 59 fax: 505 434 5555 Sunspot NM 88349-0059 web: www.apo.nmsu.edu APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 733 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-general/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO