7" LCD Panel Due 5v glitch returned

  • I had posted about this previously where the the LCD would glitch out – dim, flicker etc. I am running my duet on a dedicated 5v source and DC42 said that the there are some diodes in place which drop the voltage low enough where the LCD will have issues. So I had raised the 5v PSU to 5.5v, and it was fine for a while, until the latest LCD firmware. The screen is has less flicker and is faster with the latest firmware, but yesterday I noticed the screen having another voltage related spasm. I have a readout on the 5V rail and it's showing 5.5v steady, and the current use is spiking when the screen is freaking out. To test a theory that the diodes are messing with the 5v rail going to the LCD, I bypassed the 5v pin on the panel due connector and fed it the 5V line directly, and glitches stopped and the screen is much more stable. Is this only an issue with using a dedicated 5v supply? Somehow this wasn't a problem with earlier panel due firmwares -- it ran fine with the diode dropped voltage from the duet 5v panel due header.
    As I understand it there are 2 diodes involved, one on duet and one on the panel due -- so voltage drop is as much as 1v -- so if I'm feeding 5.5v, it gets dropped to 5v by the duet at the input, and then the panel due is dropping it to 4.5v -- and apparently that's too low now?


  • administrators

    My 7" PanelDue is powered from the Duet's 5V regulator, which produces about 4.97V according to my multimeter. I've not had a problem with the LCD. However, I have heard of other PanelDue users with the 7" screen that have had similar issues to the ones you are reporting. I have the impression that the backlight inverter on those displays may be marginal. Perhaps the backlight inverter chip is overheating, cutting out briefly, then when it starts up again you get the current spike.

    We stopped selling the 7" version a while back because of quality issues with the 7" TFT panels.

    Some users are now running a 7" CPLD display instead of the SSD1963 one. It needs slightly different firmware, so there is now a 7.0C build configuration. I haven't tried that display myself.

  • The case is pretty tight – I believe it's for the original 7" LCD + PanelDue -- I basically took your thingiverse object and just added mounting holes to mount it on the 2020 upright which gives best access to the display, it's not the new version which is a combo unit. Would redesigning the case to give the display more air be helpful? I measured the voltage on the 5v pin of the LCD header and it's 5v dead on, as it's being dropped .5v by the diode on the way in, presumably when I switch the jumper from internal 5V source to external 5V supply, the duet's 5V regulator is not used, but regardless my 5v rail is clean and dead on. Maybe adding some heatsinks on the backlight would help? Or would this overheating issue would be something that would be covered by warranty?

    Edit: is there some screen saver/sleep functionality that you can add to the LCD firmware -- maybe something along the lines to have the display go to sleep if not in used -- maybe an option to keep the display always on when printing, but otherwise turn off the backlight after X # of minutes when inactive

  • administrators

    There is currently no automatic screen dimming facility, but I will probably add one soon.

  • @dc42:

    Some users are now running a 7" CPLD display instead of the SSD1963 one. It needs slightly different firmware, so there is now a 7.0C build configuration. I haven't tried that display myself.

    I'll find out soon enough. I did some research into it, and it seems that it's a more stable and more power LCD – ordered it. Wonder what to do with my current LCD when it arrives, from seeing YouTube videos it never worked quiet right -- it always has these lines going through it -- like scan lines or interference -- not sure what. New firmware virtually eliminated them, and running direct of the 5v supply has made it more stable, but seems like the CPLD version is quiet a bit better. I still plan to re-design the case. Looking at possibly adding vent holes in the back plate for heat dissipation.

  • DC42, I got the new LCD and it's definitely better, the screen has no interference. However it will not run stable of the 5v line on the LCD header. I checked and it's feeding only 4.7v. The 5v supply is 5.5v, so that's a big drop on the 5v line going to the LCD.

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