Replacing Character LCDs

Replacing character LCDs comes as an unexpected and unwelcomed addition to your already long list of tasks to accomplish. For years, Focus Displays has been helping customers with this task. Below are a few key points to help you when you’re faced with replacing character LCDs.

  • Low cost
  • Easy integration into your product
  • Standard configurations
    • 8×1, 8×2, 16×1, 16×2, 20×1, 20×2, 20×4, 40×4

Character LCD Manufacturers

There are several character LCD display manufacturers in the market today including Densitron, Optrex, New Haven and Handtronix.

It is not uncommon for these Liquid Crystal Display suppliers, and others, to discontinue a specific display or to increase their lead time to you: the customer. When this occurs it may be necessary for your company to locate a replacement LCD display. When searching for a second source, here are two key points to keep in mind.

1. Character LCD Controller/driver chips

Not all LCD display controllers are created equal. When replacing character LCDs it’s important to order a sample of a replacement character LCD display, with the same controller chip. The majority of alphanumeric displays contain a controller/driver IC chip whose job function is to interpret your firmware and then display letters, numbers and punctuation on the LCD screen.

LCD driver chips are 99.9% compatible with each other, but they are not all created equal; in other words you may not be able to swap out your current driver chip with the new IC driver. Your firmware may behave differently with the new chip and the result will be unexpected characters; when you were expecting an ‘A’, you receive a 3.

When ordering a replacement sample for your display, make sure to request the same manufacture and model controller driver chip as the one you currently have in production. If the IC supplier has announced an end-of-life for their product, you may need to look at other solutions including:

  • Last time buy (ties up cash)
  • Rewriting your firmware (may not function for replacements in the field)
  • Have your samples built with different controllers to see how your firmware performs on each one.

2. LED Backlight Polarity

The beauty of LED backlights is that they are Direct Current (DC), which means you are not required to deal with an inverter and there is no worry about the issue of noise generated from the AC signal. The down side of LED backlights is that the polarity needs to be correct. So when crossing over your discontinued character display, you have a 50/50 chance of receiving a sample with the correct LED backlight polarity.

The majority of customers drive their LED backlight from pins 15 and 16, although a small minority do pull their backlight power from pins 1 (VLCD) and 2(Ground).

If the backlight polarity of your current display is reversed from that of the possible replacement display, one possible solution is to modify the jumper settings on the back of the Printed Circuit Board (PCB).

Simply removing the solder from one Jumper and add to another jumper. This will reverse the polarity of the backlight.

Contact one of Focus Display’s technical support people if you need help in identifying the correct jumper. Focus Displays is able to make this modification for you at our manufacturing level with little to no extra cost or lead time.

Challenges in replacing character LCDs

There are other challenges to be aware of including modifying the bezel, the diameter of the mounting holes and the thickness of your LCD. These are all modifications that we can implement so that your replacement character display is compatible with your discontinued character display module.

Ready to start? Call us today at (480) 503-4295.