Positive 16x2 RGB LCD not working, no backlight
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Positive 16x2 RGB LCD not working, no backlight

by tnagy14 on Fri Jan 25, 2013 10:57 pm

I just finished putting together the Positive 16x2 RGB LCD arduino 2wire shield kit and I can only see the black squares and adjust their contrast. No backlight or display will come on with the example code.

Note: I have already checked the solder joints carefully and checked I am using the correct example code.

While assembling I noticed a surface mount capacitor (C5) was not connected. The cap was only soldered on one side of the pads. I assembled the unit as is with no success and also disassembled and connected the cap. Still no backlight

The cap being mis-placed makes me question the other empty resistor pads on the board. (R8 and R4).
Is this normal for these componenets to not be there and the cap to not be connected?


Could you send a picture of the back of the LCD showing the surface mount components?

Thanks,
Tyler
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Re: Positive 16x2 RGB LCD not working, no backlight

by adafruit_support_bill on Sat Jan 26, 2013 7:54 am

The resistors are configuration/programming resistors for the lcd controller and it is normal for some of them to not be installed. The partially soldered cap is likely a problem, but it would not affect the operation of the backlight.

Post photos of the front and back of the shield & we'll take a look for any other likely causes.
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Re: Positive 16x2 RGB LCD not working, no backlight

by tnagy14 on Sat Jan 26, 2013 11:15 am

Image
Image

I would like to hook up only the LCD and power on the backlight. What pins are required to do this, Vcc, Gnd of cource but do the R G B pins need anything?
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Re: Positive 16x2 RGB LCD not working, no backlight

by adafruit_support_bill on Sun Jan 27, 2013 7:16 am

This tutorial shows you the basic wiring for a monochrome display backlight. This should light up the Red part on pin 16. The RGB displays have an extra 2 pins. Pin 17 controls the Green and pin 18 controls the Blue. http://learn.adafruit.com/character-lcd ... racter-lcd
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Re: Positive 16x2 RGB LCD not working, no backlight

by tnagy14 on Sun Jan 27, 2013 12:57 pm

I wired up the pins as shown and the backligh came on, all three colors worked. I then mounted the LCD on to the 2-wire kit board and no backlight. I tried the example code from the end of the tutorial that sweeps through the colors. Note, that this was without the capacitor and of course I cant find it anymore so kinda SOL now if the cap is needed to program it. Any idea what size cap it is so I can get another? Also, is there any possiblility of exchanging this LCD since it came assembled wrong?
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Re: Positive 16x2 RGB LCD not working, no backlight

by adafruit_support_bill on Sun Jan 27, 2013 2:01 pm

We can replace the display, but as your test demonstrates, the cap is unrelated to the backlight control. We should try to diagnose that problem first.

You solder joints look well-formed, but a little 'frosty' in appearance. What kind of solder are you using?
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Re: Positive 16x2 RGB LCD not working, no backlight

by tnagy14 on Sun Jan 27, 2013 9:41 pm

60/40 Rosin Core. The "frost" your seeing is probably the excess rosin that I scraped off. To me the problem seems to be with the 2-wire adapter board. I measure pin 15 (BLK) and it shows 5V but the R, G, B pins (16, 17, 18) are at 3V. Im do not known how this works but I would think these pins are pulled to ground by the IC to turn on each different color backlight. These Voltages do not change with 2 different example programs running.
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Re: Positive 16x2 RGB LCD not working, no backlight

by adafruit_support_bill on Sun Jan 27, 2013 9:58 pm

A frosted surface with 60/40 solder can indicate a 'cold joint'. Cold joints can have low or intermittent conductivity. Since all your components appear to be placed correctly, the most likely cause of the problem is a bad solder joint somewhere. Re-touch any joint that does not have a smooth and shiny surface. You might want to read through our Guide to Excellent Soldering first.
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Re: Positive 16x2 RGB LCD not working, no backlight

by tnagy14 on Sun Jan 27, 2013 10:18 pm

The solder joints all look good, any other suggestions? Can you offer me a schematic or anything so I can troubleshoot this?
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Re: Positive 16x2 RGB LCD not working, no backlight

by wallykissel on Mon Jan 28, 2013 1:34 am

Curious to find this post. I just assembled today an RGB LCD kit (positive) and I'm also having a problem. I've built many hardware interfaces; started back in the 1960's. (ya, OK, I'm old!) The assembly instructions for this kit were excellent.
As I assemble a project, I use an eye loupe to inspect each solder connection. My symptoms are:
on power up and adjusting the contrast pot, I get one (1) row of boxes on the display. Contrast pot is almost all the way CCW. "Hello World" sketch seems to hang at the call to lcd.begin. I'm using a Arduino compatible "Funduino"
as a Duemilanove. Any advice would be most appreciated.

Thanks,
- Wally
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Re: Positive 16x2 RGB LCD not working, no backlight

by adafruit_support_bill on Mon Jan 28, 2013 7:35 am

@tnagy - The schematics and board files are all here: https://github.com/adafruit/Adafruit-RGB-LCD-shield
btw: What processor are you connecting this to?

@wallykissel - It sounds like an i2c communication problem. I am not familiar with the Funduino, but we have seen problems with some of the clones. If you post photos of the front & back of the board, we can check your assembly.
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Re: Positive 16x2 RGB LCD not working, no backlight

by tnagy14 on Mon Jan 28, 2013 12:20 pm

I am using an Arduino Mega 256 Rev 3. Thanks for the link
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Re: Positive 16x2 RGB LCD not working, no backlight

by wallykissel on Mon Jan 28, 2013 12:24 pm

adafruit_support wrote:@tnagy - The schematics and board files are all here: https://github.com/adafruit/Adafruit-RGB-LCD-shield
btw: What processor are you connecting this to?

@wallykissel - It sounds like an i2c communication problem. I am not familiar with the Funduino, but we have seen problems with some of the clones. If you post photos of the front & back of the board, we can check your assembly.


Post photos of the back? Sounds like a de-soldering challenge. I will borrow a friends stock UNO tomorrow and try the 'Hello World' demo.

- Wally
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Re: Positive 16x2 RGB LCD not working, no backlight

by adafruit_support_bill on Mon Jan 28, 2013 12:44 pm

@wallykissel - The solder-side of the shield is more important and there isn't much under the display anyway. I wouldn't bother de-soldering the display.
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Re: Positive 16x2 RGB LCD not working, no backlight

by wallykissel on Mon Jan 28, 2013 4:29 pm

wallykissel wrote:
adafruit_support wrote:@tnagy - The schematics and board files are all here: https://github.com/adafruit/Adafruit-RGB-LCD-shield
btw: What processor are you connecting this to?

@wallykissel - It sounds like an i2c communication problem. I am not familiar with the Funduino, but we have seen problems with some of the clones. If you post photos of the front & back of the board, we can check your assembly.


Post photos of the back? Sounds like a de-soldering challenge. I will borrow a friends stock UNO tomorrow and try the 'Hello World' demo.

- Wally


I'm open for suggestions on how to view the .brd and .sch files. @ https://github.com/adafruit/Adafruit-RGB-LCD-shield

Thanks,
- Wally
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