One pad had N/C (I could find) the other pad goes to pin 15 of the i2c chip.
I was using a ohm meter to verify connections but it is sometimes hard as there is some connections that are made but with resistance.
No I did not run guesser, But keep in mind the tint of the whole display slightly alters when I send the BaCklight on and off commands.
Here is the contructor
LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Set the LCD I2C address
Also note I changed the Positive to Negative and the tint that I saw in the lcd was reversed when Backlight was on and off.
Thus no blue tint when backlight(), and a slight blue tint on nobacklight();
Again, the gap between the LCD and the backpack is like 1/16" to 1/8" I really can not see under it, I tried last night with a flash light and today tried again, (eyes are better as it was late last night) There maybe 1 part underneith the backpack. Looks like maybe a surface mount resister located near the i2c chip and the 2 pads. but not directly under the 2 pads.
Below is best I could figure out with connectivity testing
Notch at top of this map marked by a 'U'
I2c pinouts
VCC----- U-------LED Shunt and VCC
VCC --- ----SDL
VCC--- ----SCL
R/S --- ----N/C
R/W--- ----D7
e------ ----D6
??----- ----D5
Gnd --- ----D4
the ?? pin had high resistance connections to may pins
1 pad was connect to the VCC and shunt, I could not find any connect to the other pad, Not even a high resistance one.
Is there 2 pins that I can ground and VCC on the LCD to turn the Blacklight on just to test if the backlight is the issue??
Actually that could be seen as confirmation of bperrybap's last post.
Your ?? pin is what is called P3 in the chip's datasheet.
And you being unable to measure where this goes does also hint to a transistor connected to it.
Wait a bit for confirmation from rnguyenvn1995 as requested by bperrybap.
The connections to the PCF8574 look ok.
It is starting to look like P3 goes to a transistor on the bottom of the board.
If there is, then the polarity will be NEGATIVE as there is more than likely a
PNP transistor to turn on the VCC to the backlight anode.
One pad had N/C (I could find) the other pad goes to pin 15 of the i2c chip.
This is very odd. If the other pad was VCC, then it might make sense as that would
allow a pullup for the SDL line if a resistor was soldered in.
What about the bottom jumper wire/pin?
I didn't see any mention of that.
Is there 2 pins that I can ground and VCC on the LCD to turn the Blacklight on just to test if the backlight is the issue??
Yes. Good next step.
I would recommend using a resistor just in case the baclight needs one.
So this is what I'd do.
Remove the jumper.
Hook ground up to the ground signal on the I2C header.
(Don't hook up any other wires on the i2c header)
Then use a 80-100 ohm resistor and connect one end to VCC
on the arduino.
Connect other end to pin 15 of the LCD.
That will isolate the power for the backlight and light up the
backlight.
Don't expect any pixels, we are just looking for the backlight
to light up.
One thing that might be going on is either a blown backlight LED
(from not use a resistor). Or a blown transistor, or perhaps
something is shorted on the back of the board.
If you don't have a resistor, as a quick test, you can touch vcc
directly to the Anode pin (pin 15 of the LCD). But only very briefly.
If the backlight is good, it should light up.
(again, make sure the jumper is removed)
If the backlight lights up then something is wrong
in the backlight circuit controlled by P3.
Touched pin 15.... with ~ 100 ohm resister... I think my meter said 110
Nothin at all!!!
So I guess that I have a dead backlight
It should be noted that MY LCD looks a little different then that in the picture
Highflier
Attached is a video of what goes on with my screen while I have a flashlight aimed at it. Not I have 3 backlight on/off commands with a delay between it.
Well,
Today the Chinese vendor replacement unit showed up. No charge, and guess what, ran my code without a line of change and poof it works. So for what ever reason the backlight on the other unit is just Fubar.
I find that the display is quite easy to read after adjusting the contract pot.
Once again to all those who commented and tried to help Thanks 8)
