blgli
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Replacement controller LCD screen going up in smoke

Mar 17, 2019 5:17 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 ever 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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guy.k2
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Re: Replacement controller LCD screen going up in smoke

Mar 17, 2019 7:02 am

I don't think pin 15 on the Midas is the same function as on the BuyDisplay board.

15 and 16 are backlight anode and cathode to power backlight for the Buydisplay,

Pin 15 is a negative voltage output on the Midas going to an off-module contrast control.

Midas backlight is powered by Pin 16 (cathode) but rather than pin 15, backlight cathode goes to vdd via a resistor,

blgli
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Re: Replacement controller LCD screen going up in smoke

Mar 17, 2019 10:19 am

guy.k2 wrote:
Mar 17, 2019 7:02 am
I don't think pin 15 on the Midas is the same function as on the BuyDisplay board.

15 and 16 are backlight anode and cathode to power backlight for the Buydisplay,

Pin 15 is a negative voltage output on the Midas going to an off-module contrast control.

Midas backlight is powered by Pin 16 (cathode) but rather than pin 15, backlight cathode goes to vdd via a resistor,
I kind of assumed that both pin 15 & 16 serve the same purpose across the two displays. Ground and power respectively. Maybe I’m wrong. Do you think it’s possible to use the Midas display? Or am I just asking for too much?

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guy.k2
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Re: Replacement controller LCD screen going up in smoke

Mar 17, 2019 4:01 pm

I think you can eventually get it working, but need to change how pin 15 is connected to match the circuit diagram in the Midas spec sheet. They don't specify the resistance between it and Vdd.

My approach would be to check if data and and display will even operate would be to connect everything EXCEPT pins 15 and 16.
That should let the rest of the display operate. You won't have any backlight, but can illuminate it from the front to see if proper text is appearing. It will be faint, but detectable.

If you get text display, you know the data lines and LCD controller are working.

I would attach pin 16 directly like the other pins.
Smoke test. If that passes...

Pin 15 (Vee), I would route to a variable resistor wired as in their diagram for external contrast control...
Screen Shot 2019-03-17 at 9.04.12 AM.jpg
Screen Shot 2019-03-17 at 9.04.12 AM.jpg (72.02 KiB) Viewed 153 times

blgli
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Re: Replacement controller LCD screen going up in smoke

Mar 17, 2019 5:39 pm

guy.k2 wrote:
Mar 17, 2019 4:01 pm
I think you can eventually get it working, but need to change how pin 15 is connected to match the circuit diagram in the Midas spec sheet. They don't specify the resistance between it and Vdd.

My approach would be to check if data and and display will even operate would be to connect everything EXCEPT pins 15 and 16.
That should let the rest of the display operate. You won't have any backlight, but can illuminate it from the front to see if proper text is appearing. It will be faint, but detectable.

If you get text display, you know the data lines and LCD controller are working.

I would attach pin 16 directly like the other pins.
Smoke test. If that passes...

Pin 15 (Vee), I would route to a variable resistor wired as in their diagram for external contrast control...
Screen Shot 2019-03-17 at 9.04.12 AM.jpg
I just tried what you mentioned above there is no text on the Midas display when all pins but 15/16 are hooked up. Tried the same with the buydisplay lcd and I can see text but obviously no backlight was on.

I have them hooked up in a breadboard this time so I can get this working before final soldering of everything. LCD controller is brand new and works with a brand new buydisplay LCD, but does not work with a brand new Midas LCD when the backlight is disconnected (pin 15/16)

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guy.k2
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Re: Replacement controller LCD screen going up in smoke

Mar 17, 2019 6:35 pm

So either the Midas is not compatible with the data signals, or it is simply fried post the magic smoke episode.

blgli
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Re: Replacement controller LCD screen going up in smoke

Mar 17, 2019 7:22 pm

guy.k2 wrote:
Mar 17, 2019 6:35 pm
So either the Midas is not compatible with the data signals, or it is simply fried post the magic smoke episode.
All the components I used to do the test without the backlight have been brand new components. Both LCD’s and the LCD controller are brand new.

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guy.k2
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Re: Replacement controller LCD screen going up in smoke

Mar 17, 2019 7:41 pm

All the components I used to do the test without the backlight have been brand new components. Both LCD’s and the LCD controller are brand new
Oh. I thought you were using one of the post smoke units with a replaced cap.

So with new components, that's not encouraging in terms of verifying compatibility. I wonder if the controller is feeding correct contrast control voltage for Midas LCD operation. What do you measure on pin 3 (V0)?

Misas spec says VDD-V0 must be between 6.2 and 6.8 volts.

Whereas the Buydisplay uses V0 contrast control at 4.5 to 5.1 volts

blgli
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Re: Replacement controller LCD screen going up in smoke

Mar 17, 2019 8:32 pm

guy.k2 wrote:
Mar 17, 2019 7:41 pm
All the components I used to do the test without the backlight have been brand new components. Both LCD’s and the LCD controller are brand new
Oh. I thought you were using one of the post smoke units with a replaced cap.

So with new components, that's not encouraging in terms of verifying compatibility. I wonder if the controller is feeding correct contrast control voltage for Midas LCD operation. What do you measure on pin 3 (V0)?

Misas spec says VDD-V0 must be between 6.2 and 6.8 volts.

Whereas the Buydisplay uses V0 contrast control at 4.5 to 5.1 volts
That may be it. Constrat pot turned all the way up and I’m reading 5v from pin 3, turned halfway down its about 2.7v.

Although I did happen to find this, article: https://discuss.toms3d.org/hardware-f6/ ... debf35857f, second post from the end. The user, ‘MatPhillips’ was trying to get the same Midas display to work on his board and the conclusion after talking to the manufacture was to hook pin 16 up to pin 16 on the controller board, isolate pin 15, and run a 9.1k resistor from pin 15 to pin 3 on the Midas display.

Currently I don’t have a 9.1k resistor here to give it a shot, going to run to the store in a little bit, but having all the pins except pin 3 and 15 connected to the controller I get backlight, just no text, but no smoke either from the controller.

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guy.k2
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Re: Replacement controller LCD screen going up in smoke

Mar 17, 2019 8:44 pm

Ah. A single 9.7k resistor. It's a simplified way to do the contrast control and get negative control voltage from pin 15 to pin 3.

You're otherwise also keeping isolated pin 3 from the controller board too, right?
If you go with the variable potentiometer circuit rather than the fixed resistor, you should get adjustable contrast.

I'm betting hard enough on your succeeding that I have ordered a Midas unit as well. The pressure is on. :D

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