My 1602 16x2 LCD with keypad had stopped displaying. I turned off the Arduino to fit a removable plug to the sensor cable and when I turned it back on the the screen lights up but won't display any characters? Its fitted on a shield so I doubt its a loose data pin between the Arduino and LCD shield. No code has been changed it was displaying perfectly before. I've rechecked the connections on my newly filled plug and everything is exactly as before power to power, data to data, ground to ground. Could it just be a faulty LCD or Arduino? Is there a simple way to test. I though of uploading an example sketch that just displays some default text.
Hi,
Can you please post some images of your project?
So we can see your component layout.
A schematic would also help.
Do you have a DMM? Digital Multimeter
Thanks... Tom... 
Also include the type of new sensor and its tech data (if it draws too much power for the Arduino).
Hello, there must be a variable POT for contract adjustment. Try to adjust the POT. If you are using a breadboard, you can change/omit that too.
Nothing has changed with the project software (code) or hardware. I simply turned the Arduino off, cut the cable, soldered the plug into the cable ends to allow the the sensors to be unplugged and moved if needed, then turned the Arduino back on and the LCD wasn't displaying any text, but was powered as it was lit up. The sensors are DS18b20 x3 and the LCD and keypad shield is a https://www.switchelectronics.co.uk/lcd-keypad-1602-16x2-display-shield-for-arduino-uno-or-mega-2560?gclid=CjwKCAjwg-GjBhBnEiwAMUvNWznYmcOliBs96ZzPafUC-pARoWnye9xkuA6RGr3LXQZGCr0LjrHGWBoCx-4QAvD_BwE.
Its controlling a 4 relay board like this https://www.switchelectronics.co.uk/12v-4-channel-relay-board-module-high-low-trigger?gclid=CjwKCAjwg-GjBhBnEiwAMUvNW0G1kTX4fLgNDqXFHU_SAMmjK-BraBkIZPJeT-xaWnKtCjXfMdtoMRoCDRcQAvD_BwE
I was just going to buy a replacement LCD /keypad shield but wondered if there is an easy way to test it or the Arduino, without removing it and de-soldering all the connections.
Hi,
Can you please post some images of your project and your new plugs/sockets.
Did you use a DMM to check the new plug/socket continuity?
The fact that you have no characters displayed, does not necessarily mean the display is at fault.
Your code could be experiencing a problem with sensor detecting and has not got to the display part of the code.
What are the sensors?
Please post a copy of your code.
Please post a copy of your schematic.
Lets get back to basics.
Have you loaded the LCD library, "Hello World" example code to JUST test the display?
Thanks.. Tom..