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13. Trouble shooting Guide

Symptoms Possible Solutions
Display appears blank 1, 2, 3, 5, 6, 7, 8, 9, 10, 12, 13, 14
Displayed data enters unreliably or at random 2, 3, 4
Missing column segments or pixels 13
Excessive heat generated by LSI chips or excessive IDD current 1, 14
Unable to read VRAM or Busy flag 1, 3, 7, 9, 10
EL Backlight will not function or is too dim 15
LED backlight will not function or is too bright or runs too hot 11


Possible Solutions:

  1. Check voltage level and polarity of VDD and VSS at display connector. The VDD logic supply voltage should be in the range 4.75VDC < VDD < 5.25VDC with respect to VSS(GND). Also check that VDD and VSS noise, is within limits.
  2. Check the pulse width of /RES is within specified limits or the T6963C will not be reset properly and internal registers will not be initialized. Also check when testing numerous displays on the same test set-up that the VDD voltage is turned off before connecting or disconnecting LCD modules. Note that on power-up the contents of the VRAM are not cleared and will contain random data. It is best to set every location of VRAM to a known state as part of any initialization procedure.
  3. Check that that all Hold and Set-up timing requirements are met as shown in section 5.1.
  4. Ensure that data is not being transmitted too fast to the T6963C. Always pole the BUSY flags STA0 and STA1 before sending instructions (section 9.2). If MPU is not set up to read the BUSY flag before writing instructions allow an adequate delay between instructions (section 8).
  5. Check the voltage level at the Vo pin is at the correct voltage for the ambient temperature conditions as specified by individual LCD module data sheets.
  6. Check the continuity of the cable between the host MPU and the LCD module. Check for broken connections, loose crimps or dry joints on soldered connections. Minimize the length of this cable to reduce cross-talk and noise pick-up.
  7. Check that the data bus of the T6963C (DB0-DB7) is not excessively loaded during read operations.
  8. Check the voltage levels of input signals is as specified by the LCD module data sheet.
  9. Check that no more than one external bus device is selected during read operations so as to cause bus contention and erroneous data transfer.
  10. Check for damage to PCB traces and plated through Via holes.
  11. Check that the correct series current limiting resistor for the LED backlight is in place between the power supply and the LED lamp. Check individual LCD module data sheets for maximum forward current, If, for LED backlight. The LED's may burn-out if the maximum forward current, If, is exceeded. Some, but not all, LED backlight modules will already have the current limiting resistor on-board.
  12. Check that Display ON/OFF flag is set otherwise display will appear blank.
  13. Check that LCD module has not been mishandled by applying excessive shock of mechanical stress which will cause the LC glass to misalign with the Elastomer strips that connect the LC glass to the PCB.
  14. Check that LCD module has not been mishandled by applying excessive electrical stress in the form of electro-static discharge (ESD) or by applying reverse voltage to VDD and VSS. Always use electro-static handling precautions, grounded wrist straps and bench mats when handling LCD modules as they use CMOS LSI chips. Always use a grounded soldering iron when mounting connectors to the LCD module.
  15. Check connections between EL backlight DC-AC inverter and the EL lamp mounted on the LCD module. Check input voltage to DC-AC inverter. Never operate the DC-AC inverter without an EL Lamp load, as this may damage the inverter. EL backlights dim with age and need to be replaced when their brightness level is no longer adequate.

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