LCD not working


I just completed the assembly of the shruthi with the SMR4 v0.7 filter board.
The LED test passed. So I’ve soldered the LCD board to the main one.
The LED test passes again, and the backlight of the LCD lights up, but no characters are displayed.
I’ve tried turning the trimpot R21many turns in each direction, but still characters are completely off.

I’ve connected a midi keyboard, and a mixer with headphones.
I can hear a veeeery faint sound, which appears to be following midi notes.
Maybe the sound is so low because the filter need calibration, but I can’t do much without the LCD working.

Any suggestion on what to check, or how to proceed?
Thanks ahead of time for any help.

Best regards,


I finally found time to finish the assembly… it seems the problem was just bad soldering (need to improve my skills here). Could not see by eye (also not too good), but after remelting here and there, everything works fine… and sounds great!

Thanks to all of you for the suggestions,

Do you see white squares on the LCD? If not, there’s something wrong with the trimmer.

Which voltage do you have at the middle pin? It must be between 0.5V and 1V for you to see something. If not, turn it to reach this voltage range.

Weak signal can be many things. Bad solder joint or one that was missed, so you are hearing crosstalk.

Could also be mixed up resistor values.

For the LCD try resoldering then GND Pad of the Trimpot, this solves 80% of the Problems that are not “turning the wrong direction”…

yes, I have installed the jumper wire.
I have tried turning the timpot of the LCD many many turns in each direction.
I also tried resoldering the the pins of that trimpot.

Still same problems as before (no characters on LCD; very very low sound: turning an encoder produce noise with comparable low loudness).

Best regards,

Have you installed the jumper wire on the audio output socket?

As for the LCD, it does take very many turns, the trimmer has a 24 turn range.

Interesting, Im going to try all of these suggestions tomorrow AM