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RC4000 ACU Boardset
4.2 Troubleshooting
This section provides tips for debugging typical problems. There are many interfaces between the
RC4000 and position sensors, limit switches, mechanical components of the mount, other satellite
equipment, etc. Some problems are due to interactions that are not readily apparent. Review all of the
troubleshooting sections to see if a situation similar to yours is described.
4.2.1 Limit Switches
The various limit switches serve as safety interlocks to prevent mount damage. The RC4000 checks for
limit conditions via both software and a Programmable Logic Device on the analog board. The following
table summarizes the interlock logic employed:
LIMIT
INTERLOCK LOGIC
Azimuth STOW
Elevation movement below the Elevation DOWN position is not allowed unless the
Azimuth STOW condition is active.
Azimuth CCW
CCW movement in azimuth is not allowed when the azimuth CCW condition is
active.
Azimuth CW
CW movement in azimuth is not allowed when the azimuth CW condition is active.
Elevation DOWN
No azimuth movement is allowed when the Elevation DOWN condition is active.
Elevation STOW
No further elevation down movement is allowed when the Elevation STOW
condition is active. NOTE: when the Elevation STOW condition is active, the
RC4000 internally generates an Elevation DOWN condition.
Elevation UP
No further elevation up movement is allowed when the Elevation UP condition is
active.
Polarization CCW
CCW movement in polarization is not allowed when the polarization CCW condition
is active.
Polarization CW
CW movement in polarization is not allowed when the polarization CW condition is
active.
Polarization STOW
Elevation movement below the Elevation DOWN position is not allowed unless the
Polarization STOW condition is active. NOTE: only certain mounts mechanize the
Polarization STOW limit switch – refer to Appendix B for your mount.
Many problems are caused by limit switches either activating incorrectly or the RC4000 not sensing the
limit switch's state correctly. The following are some examples of problems caused by limit switch
sensing:
Mount will move down in elevation but not up. Check that the Elevation UP limit switch is not stuck in
the active state.
Mount will not move below the DOWN elevation limit. Check that the Azimuth STOW limit switch has
activated correctly. Also check the polarization STOW limit switch if the mount is so equipped.
Mount will only move up in elevation. Check that the Elevation STOW limit switch is not stuck in the
STOW condition.
Mount is above the Elevation DOWN position but will not move in azimuth. Check that the Elevation
DOWN limit switch is not active.
Failure of a limit switch to activate properly may be due to the limit switch mechanism itself, cabling to the
limit switch or failure of the RC4000 to sense the limit switch correctly. Isolating the problem to the
RC4000 or switch/wiring may be accomplished by placing wire jumpers across appropriate pins on the
J13A connector (2.1.2.2.13), the J14A connector (2.1.2.2.15) and the J14B connector (2.1.2.2.16).
NOTE: only the Elevation STOW/DOWN/UP, Azimuth STOW and Polarization STOW (if applicable) are
mechanized via discreet limit switches – Azimuth CW/CCW and Polarization CW/CCW limits are
mechanized differently and will be discussed later.
Chapter 4
164
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