CFAH2004ATFHJP Blank Display

[MDavis]

I am working on a project with a CFAH2004ATFHJP. I connected the LCD and everything was working fine. I then went home for the night. When I returned to work the next day the LCD shows a blank screen with backlight on. No matter what I do I can't get anything to appear on the screen with code that worked the day before. Also the right side of the screen near the resistors is very hot to the touch. I checked all the wires and solder joints without any obvious problems. The LCD and board were sitting unplugged on an anti static mat covered in a sheet of bubble wrap all night. Just wanted to see if anyone could think of a reason or fix while I wait for a new module to come in.

Michael Davis

Crystalfontz LCD Blog

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[CF Support2]

Michael,

Did you have any current limiting in place for the back light? I doubt that having the module covered in bubble wrap would have caused the module to over heat - but if there was a component that was just withing spec, it could have failed, and it may have failed without being covered.

If you have not already, you'll want to request and RMA for the module to support@crystalfontz.com so we can get you up and running.

 

[MDavis]

The board and LCD design was actually done by a seperate company for us, and now I am just working with it and testing it. Seems like they connected straight 5V no limiting resistor on the back light. I measured the current at about 125mA. I added a pot to limit the current, and I can now turn down the back light. The screen still remains blank. I also tested Vo and found about 1.5V on it. I guess my question would be could the back light current/voltage being too high damage the whole LCD module or would it just damage the backlight itself. Also the bubble wrap was only covering the module while it was off, so that shouldn't have effected it.

 

[CF Support2]

Michael Davis,

It is unlikely that the high backlight current would have caused the LCD to fail - that would cause the backlight to fail by the LEDs being driven too hard, or at least the life or White LEDs would be reduced.

With your Vo at 1.5v, that may be the issue. Try working with this value - The spec sheets reads that the supply Voltage for the LCD range is 3.8 to 5.7 (based on temperature and Vdd-Vo).

If adjusting Vo does not produce any results, we can get an RMA going for you.

 

[CF Tech]

Vo (Pin 3) should be somewhere between (5v-3.8 = 1.2v) and (5v-5.7 = -0.7v)

I think 1.5v on pin 3 (Vlcd of 3.5v) might be a little light, but I would think it would be visible.