Easytouch LCD replacement - adjusting contrast

I recently pulled a bad Easytouch display and the contrast on the replacement made it difficult to read. I figured I'd do a writeup on how to adjust it...

Just below the 16 pin header for the LCD you'll see resistor R37, which controls the contrast. Normally these displays use a voltage divider for contrast - and there's evidence that Pentair designed it that way but they didn't populate R38.

All you need to do is adjust R37... but you have to figure out what value works best.

I found a 5k "trim pot" (aka variable resistor), set it to 5k, and soldered it in place of R37 (don't use it at 0k because that could damage the display)

I temporarily mount the new display by setting it over the header pins as if I was going to solder it... but instead of soldering I tilt the bottom of the LCD up, which puts pressure on the pins and makes decent enough contact with the LCD for the board to boot

Power up the board while keeping up the LCD pressure (could use a third hand), and adjust the variable resistor until the contrast looks good...

Shut everything down, pull off the display and measure the variable resistor... replace it with a fixed resistor that's close enough (if your trim pot is small enough you can just leave it)

I didn't have a surface mount 2.8k resistor so I used a through-hole part. If you've noticed that I've soldered to pads that don't belong to R37, good eye - but don't worry because the pads I used are connected to R37.

The original display used a 487 Ohm resistor which was fine for some replacements, but two recent display batches I got look best with a 2.8k and a 1.5k, respectively. I didn't have a 2.8k resistor so I used a 2.7k, not a surface mount part but it works...

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