LCD dark. dead or alive?

hello every one
i have a problem:
LCD does not light up, i think he is dead.
how i can check the statut of LCD?
thank you for your reply

Have you soldered the current limiting resistor (and if so, which value?)

Have you tried changing the contrast?

sorry, now is All dead: power was 14,5V on the multimeter then 9V 500mA are indicated ont the label.
no sound, no lights.
i have to check all.

Where did you messure 14.5v ? Is that the output of your power supply? Thats to high. 7.5v is enough. At 15v the ic that generates the negative voltage will break. Did you do the voltage checks of the power rails from the build instructions?

Now I work, I do not have much time, but I will not let the matter drop.

Each time I finished a build (2x Shruthi, 1x Ambika), when I switched it on the LCD was dark …

I had to change the contrast every single time: you never guess the position of the trimmer right … and often need to turn it quite a few times.

@cargo_solo: I truly sympathise, but this is a well known problem with unregulated power supplies:

“Unregulated DC wallwarts (the most common kind) are rarely labelled in a meaningful way.
As a result, be extremely cautious when using a power supply approaching the maximum ratings!”

The voltage should drop to its nominal (labeled) level when you’re drawing the rated current (in your case 500mA), but when you simply measure it with no load (as you are in that photo) it can rise considerably). However, once you’ve plugged it into your Shruthi it should drop quite a bit, so your Shruthi is unlikely to have been sent anywhere near 14.5 volts in practise.

Martin

it seems to work again, I do not have sound but I believe
apparently it is a loose connection in the LCD. I have to check the connections. patient …

The LCD has nothing to do with sound generation. These are two different issues. If your power supply really put 14,5V into the Shruthi it would have destroyed the LT1054. This would mean that there is no -5V anymore which would adequately explain the lack of sound. Can you do the voltage test on the filter board and give us the values?

apparently everything works except the LCD.
that it emits a light halo of light, but nothing comes on the screen.
there is probably a connection again, but the LCD poses problem because I do not know what functions I change by turning the knobs.

my question is: Is there a way to check that the LCD works independently of shruti?

thank you for your response.

No.

No, but in most cases the pins are tight enough to check if it is working before soldering. At least in my cases.

Did you try adjusting the contrast? If it didn 't seem to do anything , remember that it takes an incredible amount of turning to go from one end of the trimmer to the other, and at each end there is no stop, just a very faint click. If all the turning doesn’t get you anywhere resolder the three connections of the trimmer, then measure the voltage between ground and pin 3 of the LCD with different settings of the trimmer (it should change as you turn). Pin 3 of the LCD is connected to the middle pin of the trimmer but is a bit easier to reach…

if pin 1 is nearest to the katode and pin 16 the most distant
it is 4.65 V in pin 1
4,94 V in pin 6 --> 10 and 14 and 15
0 or 0.01 V in other (2,3,4,5,11,12,13,16).
firmware it must be installed to operate the LCD ?

If the chip has no firmware installed on it, the LCD displays a row of filled squares, and an empty row.

Can you confirm you tried adjusting the contrast trimmer. Be aware that it takes 25 ! turns to go from one side to the other. So only if you tried turning it 25 times one way and 25 times the other way you can be sure you didn’t miss the right spot.

OK, i am happy. i see on the LCD: "
mutable instruments v0.97
thank very much

magnifique, no?

congrats!