Troubleshooting and known bugs

• On one occasion (19 December 1995) the telescope started slewing to a random location after the focus controller was switched on. On another occasion (06 April 1996) the telescope decided to do a ``caldec'' with no warning.
• In general, if the servo-controller, Apple, or PC, crashes or otherwise gives trouble, it may be best to turn them all off and then restart from scratch following the startup procedures exactly. Any attempt to short-cut this route by, for example, not resetting the servo-controller when it is displaying AAAAAA, may not be successful.
• Sometime the PC gives an error when trying to boot the Apple over the IEEE interface. This problem may be due to a faulty IEEE cable, or a bad connection in the Apple. Try wiggling the cable and/or power-cycling the Apple and/or reseating the IEEE card inside the Apple.
• If when booting the PC you get a message at the bottom of the screen saying something like ``Time not set, run SETUP'', then press the RESET button on the PC, wait a few seconds, and hit the delete key. This will put you into the CMOS setup program. Simply choose the option ``save CMOS settings and exit'', and respond with ``y'' followed by a carriage return when asked whether you really want to do this.
• Note that the raw images are FITS but with BITPIX (meaning unsigned 16-bit integers) which SAOimage can handle, but which standard IRAF can not handle. The versions of IRAF on mistral and newt have been ``fixed'' to correctly handle this data. Michael Ashley can provide an IRAF program for reading the data.
• The FITS keywords stored with each image are currently in an experimental stage, but should be reliable.
• If the telescope hits a limit, it may not be possible to drive it off using the servo-controller. In this case you may have to set up another power supply to directly drive the motors. But first, try pressing the reset buttons on the servo controller. To bypass the controller use the Laboratory Power Supply, and connect its variable output to the outermost two pins of the motor cable (remove the cable from the appropriate servo amplifier first--it is the long circular three-pin Cannon connector). You will need to turn the current limiting right up on the Laboratory Power Supply, and experiment with the polarity of the connection until the telescope moves in the right direction. Take extreme care when doing this as the telescope is not protected against running into a stop.
• If the servo controller isn't working properly (e.g., it won't reset to 800000 when rebooted), then it may be necessary to replace one or more of the three boards. The leftmost board is the declination driver, the rightmost board is the RA driver, and the middle board is for communication with the Apple. The RA and Dec boards are identical (although there are differences in the settings of the two potentiometers...), and there is one spare that can be used for either. There is also a spare middle board.

  When swapping boards, ensure that the Apple and the servo controller are both off. Handle the boards carefully to avoid static damage (earth yourself by holding onto an earthed conductor, hold the boards by their edges). Take care to note the orientation of the various cables that plug into the boards, and write a note on the board that you removed so that it can be fixed.

  If the telescope isn't driving correctly (e.g., if the RA motor rotates too quickly, incremental encoder counts will be lost), you could try to adjust the potentiometers on the front of the RA and/or Dec board. The output voltages can be sampled between the two pins just below the potentiometers: the correct values during a slew are about 0.5V and are written on the front panel of the servo control box.

• There is a spare servo amplifier in one of the cupboards in the APT building.
• The limit switches are notorious for causing problems, and are also notoriously difficult to fix when something goes wrong.
• If a drive motor starts driving constantly in one direction, and the servo controller numbers aren't changing, try pressing the reset buttons. It is possible that the incremental encoder signals aren't getting through, possibly due to a connector problem or a broken wire.