Display Brightness Fault
There are three different methods used to control the brightness of the CMS display area: automatic method, display dimmer method and display brightness adjust method. Go to the method that corresponds to the specific machine.
Automatic Method
On machines with the automatic method, the CMS control automatically controls the brightness function; there are six brightness levels. A photosensor is located above the alert indicators within the CMS display area. If the display is too dim, check the display area for something blocking the amount of light available to the photosensor. Possible causes are: decal inadvertently placed over photosensor, dirt or mud blocking photosensor.
Display Dimmer Method
On machines with the display dimmer method, the display dimmer switch (SPST) controls the brightness function. The switch controls the dim input. When the input is grounded the display brightness cycles; first the brightness decreases in steps to the minimum level, and then increases in steps to the maximum level. The cycle repeats until the input is opened and then the brightness remains at that level.
If the display brightness continuously changes without activating the switch or does not respond correctly when the switch is activated, check the dim circuit. To troubleshoot the dim input, use status mode. The CMS connector contact for the dim input is contact 5. Check for an undesired open or grounded circuit in the harness wiring or the dimmer switch.
NOTE: On earlier CMS controls (when in status mode): To select the dim input (contact 5), ground the clear input. Also, contact 5 corresponds to alert indicator No. 12.
Display Brightness Adjust Method
On machines with the display brightness adjust method, the display brightness switch (SPDT) controls the brightness function. The switch controls the dim input and the brightness input. When the dim input is grounded the brightness decreases in steps until the input is opened or till the minimum level is reached. When the brightness input is grounded the brightness increases in steps until the maximum brightness level is reached or until the input is opened.
If the brightness of the display does not function as described, check the dim circuit and the brightness circuit. The dim input is at CMS connector contact 5. Determine the CMS connector contact that correspond to the brightness input, use the Electrical System Schematic in the machine Service Manual. To troubleshoot use status mode. Check for an undesired open or grounded circuit in the harness wiring or the display brightness switch.
