Question about 16x2 LCD Displays failing.

[EQUIS]

Hello,
I have a limited background in component level troubleshooting and am looking for some advise.

We have a bunch of industrial scales (part of a larger machine). They use a Powertip 1602F LCD Display. We are starting to have display failures. Some go blank completely but many start to get ghost squares and lines that make it very hard to read the actual characters. Both the display and the circuit board that runs the scale are about 15 years old.

My main question is whether this is most likely a problem within the 1602F LCD display or something within the circuit board that feeds the display? Is there an "easy" way to tell if the display is ok without desoldering it from the board?

The picture I posted is easier to read than when you look at the display in real time.

Thank You in advance for sharing your wisdom and experience.

 

[Minder]

If there have been consistent failures it might pay to remove one display and test it.
If you have no electronic way, the LCD guide by Julyan Ilett shows how to connect with simple switches to test.
Test the +vdc to the unit for correct voltage.
M.

 

[kellys_eye]

That just looks like a level of poor 'contrast' to me - there should be a small trim pot to adjust it. That may make a difference.

But 1602 displays are 10-a-penny figuratively and the one you have fitted seems to have the bog standard connection i.e. the 14 terminals at the bottom left so fitting a replacement should be straightforward.

 

[EQUIS]

That just looks like a level of poor 'contrast' to me - there should be a small trim pot to adjust it. That may make a difference..

There is no adjustment for contrast on the board. Do the 1602s Fail like that, would replacing it likely correct the issue or is the control circuit more likely the cause?

Thanks

 

[Minder]

As noted, for a $1.50 you can afford to change one and see,
There are many configurations for the terminations so ensure it is the same bottom left format.
The design is usually universal now based on the Hitachi HD44780 IC.
M.

 

[kellys_eye]

There is no adjustment for contrast on the board.

May be via fixed resistors off board - the contrast is on pin 3 of the LCD edge connector (usually - pin 1 is nearest the short edge of the board) but if the 5V supply has 'wandered' then this can affect the contrast too. Check that the 5V supply is within tolerance.

Be mindful of the fact that the contrast setting may also be a function of a menu setting in which case some form of D-A conversion will be done elsewhere to provide the contrast adjustment voltage.

 

[Donuts and coffee]

Do the displays flicker? If they do, then there could be a bug in the ROM code, or a bad connection. Maybe the timing could be too fast for the displays. I have discovered different microcontrollers, and even different versions of the controller on LCD displays wearing the same model number in the past. Some have different timing and initialization requirements. Hopefully replacing them works, because that would be a much easier solution.

 

[EQUIS]

Thanks for all the help. In the end the displays turned out to be failing in several of the units.
Thanks again for everyones suggestions.