Red Screen Issue

Hi everyone, I’ve recently assembled a Red Alert Shruthi (the one with the Polivoks filterboard), and, even though everything seems to work, the screen doesn’t. I’ve bought and mounted on the PCB this one ( http://es.mouser.com/Search/ProductDetail.aspx?R=NHD-0216K1Z-NSR-FBW-Lvirtualkey66010000virtualkey763-0216K1Z-NSR-FBW ) and, when I power it up, the screen doesn’t seem to work. The “white thing” on the right side of the screen lights up, and there is a faint red backlight, but that’s it. Nothing else, even if I try spinning the trimpot’s screw. There is a continuity in the electric signal’s path, so I really don’t know where the problem is. Thanks in advance.

The trimpot needs 24 turns to go from one side to the other did you try spinning it that much?

I’ve done like 100000 turns, however there is an UPDATE: if i touch the 1st and 3rd pins of the screen with the multimeter’s terminals (I don’t know how are they called) the screen works properly, but as soon as the don’t touch the pins anymore, the screen turns empty again

Have you tried resoldering all the pins on the board and the display? pin 1 is ground so could be you are not getting ground on the display and somehow it does get it through the meter.

I’ll try, however, if i touch the 2nd pin with the COM terminal of the multimeter, it shuts down for as long as I touch it, and there is a buzz

Aaaaaaaaaaaaaand it is necessary just to touch the 3rd pin with the red stick of the multimeter (not the COM one) to make the screen work, I’m going mad, seriously

Pin 3 is the contrast adjustment.
Did you verify the solder joints?

Yes, I’ve just resoldered it, but nothing has changed, however, I noticed that the screen works just when the 3rd and 4th pins are in touch by some metallic thing

Can you measure the voltage on the middle pin of the contrast pot? And on the 3th pin of the screen?
Watch out with just shorting things. It will work until you touch the wrong one and then something is broken.

It says 3,41V on both the central pin of the trimpot and the third pin of the screen. Here’s a picture of what’s my situation like

2nd, 3rd, 5th and 6th pin from the right on the display is highly suspicious!

And touching the 3rd pin

Unplug and measure resistance between the Middle Pin of the Pot and Pin 3 on top of the Display. Should read 0V. If not…… use a wire.

can you turn the trimpot and see if the voltage on the middle pin changes?

Its starting value is something like 120 ohm but it decreases very very quickly until 0,1/0,2 ohm

How high does it go?

I gave the trimmer a few spins and now it says 4,95V both on the trimpot’s middle pin and LCD’s 3rd pin

UPDATE: I really don’t know why, but now it works. Apparently, I had to spin a lot of times the trimpot’s screw CLOCKWISE, and not, ANTI-CLOCKWISE, as suggested in the assembly tutorial.

Excellent.

Welcome to the Shruthiversum™ !

ah i forget to mention ‘both ways’ in the first post…
enjoy your shruthi