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I have a 16x4 LCD (model DCM16433) that I suspect is dead. It has 14 pins rather than 16, but this should just mean no backlight. I have hooked pin 1 to Vss, pin 2 to +5 V, and pin 3 to a 10k pot, but I can't get anything to display at any contrast setting (IIRC, it should display the black character "outlines" even without any data). I know the pot works, and I know the LCD is getting power (that is, the voltage across pins 1 and 2 is +5 V). Am I missing something, or is the LCD just dead?

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The display might need negative panel voltage, especially if the display is large. Your pot now has three pins: the center pin goes to pin 3 and the two other pins go to VCC and GND. Instead of GND, connect that pin to something like -10V. If your board has an RS-232 level shifter (MAX232), you can get the negative voltage from there. Then adjust the potentiometer and see if you get dark squares.

For quick testing, you can also get the negative supply from a lab power supply or a 9 volt battery.

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Here are few things you need to consider:-

  1. make sure that both the backlight power and the contrast pins are attached to definite voltages, check using a multimeter
  2. for starting you can add 5 volts to backlight and a potentiometer to the contrast.
  3. check the read/write pin of the LCD.
  4. make sure the connections to your microcontroller are correct.
  5. check for the code that you used for possible errors

Please also share schematics and code that you used so that we can understand the situation better.

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