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I have Jazz PLC JZ20-J-T40, and i have 6 Screens on it.

I have downloaded my program successfully, and PLC has been working properly for a wery long time, (two months to be exact).

After I turned OFF and ON my PLC, it didn't displayed screens I have on it, so I thought that I have burned it, because of power or something.

I measured power supply, it was OK, so I connected Laptop to PLC.

I have successfully conected to PLC, and went online.

I have some MBs on plc that i change using plc tasters, tried that, it works just fine.

Everything works properly, except PLC Display.

U90 Ladder has an option to debug display online, so I tried that on my laptop, it shows displays as it should, but on PLC just blank screen.

I can see that PLC display is glowing a little, it just doesen't show any text that it should show.

I have tried to download again, nothing changed.

I tried to update Operating System, it says it's up to date.

Is there a way of fixing this?

Best Regards,

Nikola Ljubinkovic

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Thanks for such a quick answer, i wasn't able to find this System Integer, so i found on this forum that this integer is si7, tried to change that, it won't change from 0 to any other number. SI7 has no name in my U90 Ladder, I have newest version available.

What is this Integer you said that I should change?

Best Regards,

Nikola Ljubinkovic

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  • MVP 2023

Hmmm, I was thinking of the Vision products. I agree that I don't see any applicable display System Integers. It does sound like a hardware fail, but you should check with Unitronics Support for any procedure they might have to troubleshoot. Just email with your problem description above to: support@unitronics.com.

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I have tried to hold down info key, it does nothing.

I contacted some support, they told me to power OFF device, and hold info key and 7, then power it ON.

As they said, it should reset PLC, and delete it's Operatin System.

I did that, and connected PLC to my laptop. Downloaded it's Operating System again, and get same blank Screen, that glows a little.

I have tried to download older OS, same thing happens. I put it back to newest OS.

SB9 just turns OFF backlight, it doesen't help.

I have made some screens, and downoaded them into PLC, and in online mode i tried to switch from screen to screen. 

SI2 (Current HMI Display) says that Screend are switcing, and in online mode that shows PLC Screen, i can see different displays, but PLC just shows same blank glowing display.

I think it's hardware problem, but I am willing to try anything to fix this, before I contact my seller.

Best Regards,

Nikola Ljubinkovic

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Hi Nikola,

Save your project.

Create a new empty project with some text on display.

Download this project to PLC and observe display. Does it show text?

Set SB 9 to 1. Do you see backlight?

If empty project show text on display, PLC works, and you have to review your project to find error.

Look what you changed in project before having display problem.

*You may call display at each scan.


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I have tried that, and it just shows blank display with backlight, but it should be showing text

In debug simulation shows what text it should display, but PLC nothing, blank screen with backlight.

When I power OFF device I can see backlight go OFF, and when I power it on I can see it goes ON, but without text that it should display.

Just to say this, I have never open PLC backpanel, or experiment with anything like that. PLC has never left my desk.

It was working normally for 2 months, and this happened.

SB9 is bit that turns PLC Display's backlight ON and OFF it does not change my missing text problem (missing everything problem).

I tried to find System bit or Integer that changes value of text somehow, but I can't find it.

Is there bit like that on Jazz PLC's?

I know there is for other PLC's, I just can't find it for Jazz.

Best Regards,

Nikola Ljubinkovic

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