Non-working LCD

Situation: I have assembled the control board and the power section of the filter board.
I plugged them in and got a very blight blue LCD screen. So I disconnected the power and adjusted the trim pot. Now, I’m not too great at electronics (I follow instructions and things usually tend to work out) so I think I might have overdone it.

All i get is a black screen. The LED’s are working correctly as far as I can tell from the manuals.

I trieds to keep turning counter-clockwise for a very long time but it didn’t give me a bright blue screen anymore. Is there any way I can use a meter to check the values for the trimpot, and what value should i be aiming for?
Also, which direction should give me a higher value and which one should give me a lower one?

Thanks in advance!

The trimpot doesn’t control the LCD brightness, it controls the contrast. If it doesn’t work in one direction… try the other one (the course of the trimmer is 24 turns).

Is it supposed to stop turning at one point?

There’s a point where rotating the trimmer has no effect. You’ll notice it when it gets slightly more difficult to turn, and when it clicks at each turn.

I have a similar problem. The manual say: “Turn the screw of the trimpot R21 counterclockwise until you have reached the end”, but I never find the end, equal in clockwise direction, no “more difficult to turn” or “clicks”. The diference turn counterclockwise/clockwise: If i turn counterclockwise long time… I see “Foto 12.jpg”. My LCD is broken?, the trimpot?

There is a slight click at each turn when the trimmer has reached the end. It’s not loud, but it’s there.

This line of filled characters indicates that the LCD is functional but has not received an initialization command from the MCU.

Are LEDs 3 / 7 being lit when you power the unit on? If yes, there is a bad solder joint somewhere on the LCD module pins or near the MCU. If not, the MCU is not correctly inserted or the socket is not correctly soldered (though you should have tested that before soldering the LCD as explained in the assembly instructions).

Now, i can see initial text in the LCD , but when I pulse any control… return to the previous image :S. You know it could be happening?.


Yes, LEDs 3 / 7 being lit. I will review the solder.

There’s probably a weak soldering point on the 1x16 LCD connector.

The weight of the LCD puts a little pressure on the LCD joints. So they need to be perfect.

I checked all the soldering point (include the first LCD connector) and… nothing, remains the same. Another thing?.
I pulse any control in the dark … I managed to generate sounds, therefore I think the problem is near to the LCD.
is possible that the LCD circuitry (1x16) is broken?

I have never seen damaged LCDs on my side. To me it looks like a weak soldering point:

  • On the 1x16 connector, LCD module side.
  • On the 1x16 connector, control board side.
  • On one of the MCU socket pins.

Please check that the MCU is firmly inserted.

I wonder if the contrast trimmer is damaged?

I think he’s getting the backlight, no issue there. But the display is not initialising correctly, so it remains with a block pattern on the top row.

What about the connections from the ATMega to the display, are those joints fine?

Well the LCD looks exactly like that before the contrast trimmer is adjusted, right? Anyway, that was my (confused) thinking.

The top row is all solid squares which either means the CPU isn’t working (which it is because it plays sound) or the CPU->Display communication isn’t there. It is intermittent and it could be the display is losing power and restarting, so it needs initialising again before it will work.

I guess another thing to ask is if the PSU is up to the job? perhaps it isn’t delivering enough current?

I tried everything you say and seems fine. I think that both soldering and desoldering … may have broken some “pin” of the PCB. How I can check?

The best option would be to check for continuity between the pins of the LCD module and the pins of the MCU.