December 6, 2004 68P81083C20-D
9-24 Troubleshooting Troubleshooting Chart 1-8B, Control Head Models II & III
Keypad Backlight
All LEDs off or always on
1. If all keypad LEDs are OFF (or ON but never turns off), check Q0650, Q0651 and Q0652.
2. The backlight flip-flop can be turned on by connecting the base of Q0651 through a 4k7 ohms
resistor to 5 VDC and turned off by connecting the base of Q0652 through a 4k7 ohms resis-
tor to 5 VDC.
Light missing from some LEDS
Check the LEDs.
LED indicators
1. Check that the outputs from U0654 pin 6 (yellow), pin 9 (red) and pin 12 (green) change to 5
VDC when LED should go ON.
2. Check Q0657 (yellow), Q0658 (red) and Q0659 (green).
3. Check LEDs.
LCD backlight
All LEDs
If backlight cannot be turned on or off.
1. Check that U0654 pins 16 and 19 are 5 VDC.
2. If not, check U0654.
3. Check that the voltage of base on Q0666 is 5 VDC.
4. Check that the DC voltage of U0656 pin 1 is approx. 4.3 V.
5. Check Q0667 and U0656.
One/some LEDs
1. One LED is off. Check the LED.
2. One row of LEDs is off. Find the LED that makes the short circuit.
LCD
Defect Outside Segments of Display
If the LCD has either light or dark areas outside the segment, the LCD glass is defect and must be
replaced.
Missing Segments
Most likely caused by a bad connection between PCB and LCD. Disassemble and clean PCB and
zebra connector with alcohol. LCD glass surfaces can be cleaned with distilled water with 3%
ammonium chloride; never use alcohol on the LCD glass. If necessary replace the zebra connector
or LCD.
Weak Segments
1. Segment brightness depends on the text displayed. Most likely caused by a short between
the lines from display controller/driver to LCD. Disassemble and clean PCB and zebra con-
nector with alcohol. If necessary replace the zebra connector.
2. Check U0651.
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