blgli
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Replacement controller 20x4 LCD screen going up in smoke

Mar 17, 2019 5:19 am

So I’ve been wanting to change the LCD color of my Prusa MK3S and MK2.5. As we know they both use the ramps 2004 lcd controller with a soldered on 20x4 character lcd display.

At first I bought some white text on black background from BuyDisplay ERM2004DNS-1 https://www.buydisplay.com/default/3-3v ... h-contrast. Soldered it on to my controller board and all was well. It was white text on a black background. Although it was a FTSN lcd display so the backlight bleeds through a LOT, more than I liked. So I searched the internet for some better performing LCDs. Came across the VATN displays from Midas displays MC42005A12W-VNMLW https://uk.farnell.com/midas/mc42005a12 ... dp/2483356, bought two since they claimed to be a cheaper alternative to OLED. Frankly I wanted the OLED look but didn’t want to recompile firmware with every release from Prusa having to add the OLED library. Both displays are parallel interface, 5v, HD44780 compatible controller and the pin outs are exactly the same according to tech spec sheets from each respective website.

Now I can’t figure out what I am doing wrong. Soldered one of the new Midas displays on, backlight turns on, no text, few seconds later a puff of smoke from the back of the LCD and its dead. Turns out C2 surface mount capacitor burned on the back of the LCD. Thinking I maybe bridged two pads when soldering the second time around I double checked all my soldering by making sure there was no continuity between adjacent pins. Plug it in, power up the printer and poof, smoke and LCD dead again. Same capacitor burned up.

I’m lost as to what could be the cause of this, as on paper they seem to be the same displays just different LCD technology. But something isn’t right if I’m burning them up.

BuyDisplay ERM2004-1 Tech sheet, pin out is on page 9 https://www.buydisplay.com/download/man ... asheet.pdf

Midas MC42005A12W-VNMLW Tech sheet, pin out is on page 5 http://www.farnell.com/datasheets/1934384.pdf

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vintagepc
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Re: Replacement controller 20x4 LCD screen going up in smoke

Mar 17, 2019 11:44 am

your display is not pin compatible on pin 15. You may be able to get away with leaving just that pin disconnected and have it work, but you should figure out what it is meant for and wire it up correctly. (Data sheet doesn't say much about it, unfortunately)

blgli
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Re: Replacement controller 20x4 LCD screen going up in smoke

Mar 17, 2019 4:19 pm

vintagepc wrote:
Mar 17, 2019 11:44 am
your display is not pin compatible on pin 15. You may be able to get away with leaving just that pin disconnected and have it work, but you should figure out what it is meant for and wire it up correctly. (Data sheet doesn't say much about it, unfortunately)
I am going to reach out to Midas displays and see what they say. I initially thought that there was a difference between the two displays on pin 15/16, but when I tried reversing polarity on those pins the backlight would not turn on.

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guy.k2
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Duplicate thread

Mar 17, 2019 4:34 pm


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