Second opinion on my diagnosis - Hayward GLX-PL-LOC-P-4 Pool Controller

[Daveedius]

I'm repairing a Hayward GLX-PL-LOC-P-4 due to the LCD not displaying any characters; the backlight comes on and other control buttons appear to be working. Info about the board:

- PIC16F913 uC
- NHD-C0220AA-FSW LCD (obsolete, no pin-compatible replacement)
- LCD receives 3.3V directly from one of the uC's GPIO pins.

Upon intial inspection, I discovered that the bypass cap for the LCD was badly corroded & gave no sensible reading from my LCR meter. Replacing the cap with a 1uF one made no change.
From there, I switched to my scope, and verified that the uC is indeed sending data to the LCD. After digging a little deeper, and checking the power rails, I discovered that the microcontroller is resetting the power to the display every 4 seconds.

Now from this information, I'm presuming that the LCD is dead. When it doesn't respond to the uC within 4 seconds, the uC power cycles the display in a desparate attempt to get it to work properly again. What are your thoughts on this theory?   

[Swake]

Sounds like you're right but of course it is difficult to say for sure. Two other hypothesises: Did the µC pin that powers the display fail, or did the power supply kinda failed and can't handle that additional current anymore? I guess you would have noticed that last one as you measured the power supply already.


Datasheet to your display: https://www.digikey.com/en/products/detail/newhaven-display-intl/NHD-C0220AA-FSW-FTW/2626392

It is a 3.3V and 2x20 character display. On their website NewHeavenDisplay offers these displays: https://newhavendisplay.com/lcd-displays/character-displays/?Size=2__Rows__|__20__Characters&filterPage=1

It seems the NHD-C0220BA-FSW-FTW-3V3 might be the right one to replace your current display. You'll have to verify all specs. 12 bucks is not the end of the world if it turns out the issue is not the display.

Seems the Novatek NT7605 controller on that display is only slightly different from the pseudo standard HD44780 protocol too.

[Daveedius]

Turns out it was indeed the display. Couldn’t find them anywhere so I had to find a repair service that had some donor boards. Unsure if the new display you listed would work but I agree, it would be worth  checking out if I have to repair anymore of these boards.