1602 Display Problem

[radiotec]

1602 Display Problem

I just turned on my LC-100 LC meter and the display is really weird looking.
If I turn the display at a certain angle I can just about read what it normally displays and it looks like its working.. Not sure what to do, I was thinking about disabling the back light but I really do not think it would help.

Any idea what these characters are that are being displayed and how to get rid of them ?

Any help would be appreciated.

 

[Bluejets]

Contrast set too high perhaps............
Can read MEASURE Cx OVER RANGE

 

[kellys_eye]

There should be a small potentiometer (perhaps with blue body and tiny brass adjustment screw on it - might just have a simple screwdriver slot) situated under the display somewhere. Give it a 'spin' with a small screwdriver whilst watching the display.

 

[radiotec]

There is no adjustment pot.

Pin 2 VDD IS 5 volts and pin 3 is .117 volts

 

[danadak]

Pin 3 typically 2 - 5V, sounds like its shorted to ground. I have used many
where I operated them a diode drop below 5V, eg. 4.3V.

Pot could be under display, would not be the first time I have seen that.

Post a pic of the underside of the board the display is soldered into and post it.

Regards, Dana.

 

[radiotec]

Well, there is a picture off the back side.
Just noticed it, there is no trace coming off of pin3.
I think that I may just have to replace the display.

 

[Bluejets]

Well, here is a picture off the back side.

That is a 16x2 but what was meant was, ................show a photo of the back of the one on you tester.

Difficult to get at as the LCD is mounted with small spacers on top of the main board.

Appears though, from the link below, this is a fixed resistor.
There is a mod mentioned under "contrast".

https://ludens.cl/Electron/LC100A/LC100A.html

 

[radiotec]

Yes, I did remove the spacers and thats what the back side looks like.

 

[Bluejets]

Circuit diagram

 

[radiotec]

Hi Bluejets, I Really appreciate the schematic and the LC100 mod pages. I measured both sides of R1 to VO pin 3 and and got 8.2K and 10.5K. I then measured across R1 and got 2.2K. I think that eighter the schematic has errors or it is a different version then my LC100. Anyway I will probabbly install another 1602 tomorrow and I will let you know what happens.

 

[Bluejets]

I think that eighter the schematic has errors or it is a different version then my LC100

Yes, could be, no way I could tell from here sorry.
LCD contrast would be adjusted the same though whatever model of LC100 you have there.
Would need your tracing the tracks and measuring any voltages.

Note that many schemetics requiring the contrast pot to have one leg connected to the 5v supply has been shown to be incorrect in the past as there is already a 5v tied internally only requiring a variable or fixed resistance to ground.

 

[kellys_eye]

Manufacturing differences mean they have to include a contrast adjustment and using a fixed resistor for a 'mass produced' item gives rise to the odd device not having the right value due to those differences.

Remove R1 and fit a preset pot (10k) or slap in a higher/lower value to see the difference it makes. Note also that ambient temperature can also affect display contrast so a preset adjustment is probably the best way to go.

 

[Bluejets]

Did it ever work properly..??

 

[radiotec]

Good news ! The new 1602 display that I purchased from Amazon works great.

Thanks everyone, I appreciate your help.