Others LCD Problems


i finished to build my SMR4MKII, but i have a problem with my LCD; i turned the trimpot in every position and more as 23 turn, but i can’t put the contrast down, it’s so much lighting, so i can’t see the letter properly on the screen. also my trimpot don’t have “end”, i turn it in every position but nothing change. i resolded the trimpot, but maybe it’s fried ?

i also find my output a bit low, for example : in fruity if i connect it, and play it, it’s like -18Db on the vumeter. it’s normal ?

I have also another problem with the screens (but maybe it’s the firmware), when i put the filter at 127, it’s always on the screen and something there is som bug and i can see it flashing… Someone had already this problem ?

Thx, Bye

if you can, post some pictures of the lcd when its on.

  • If your Display is to bright you can make R20 (should be R68) a bit bigger (say R100 or R220) this should dim the Display.
  • Trimmmers never have an “end” (to prevent you from breaking…) you just hear a faint Click when turning.
  • The VUmeter in a Software is quite pointless as (especially on Windows) never know which Gains are applied form your Soundcard/Drivers/Whatever till it reaches your Software, can we have some readings from a Hardware Mixer or something? Is the Sound only faint or is it distorted? If its undistorted check all the Resistor Values around IC2, especially R6, R10 and R4.
  • If a Value Floats (flickers) its most likely an bad Solder Joint somewhere, resolder the Pads at the Pots and the ones from PIN 37-40 on the ATmega

The floating Value seems to indicate not so perfect soldering, so maybe you will also redo the Pads around the Display and the OutPut Stage of your Filter (IC2)

Hey Lamouette, if your goal is not to learn DIY electronics and you just want a working Shruthi you can send your boards to me and i’ll try to revive them for you for free: you’ll only have to pay shipping (i’m in California) and for dead components that would need to be replaced. I have all the necessary tools (including Hakko 808 de-soldering station) and just finished building my third Shruthi.

Hi, i add some photos : i again resold a lot of points and they look like good, but alwys the same problems. i will try to unsolder the screen to resold the point behind.

fcd72 :

  • I don’t think it’s to bright, the problems is the contrast (see on the photo), but maybe you’re right.

  • i don’t have any hardware mixer, i connect directly the shruthi- on my soundcard (an MOTU Audio express), and with the maximum input gain, i can read -18Db on the input of FLStudio (i will try to do some screenshots, and records of it)

  • I also have a little problem, whem i assemble the 2 card, the ATMega touch with the neutrik jack, and i sould screw it hardly to be sure it fit perfectly. It’s normal ?


Your R20 is 67.2 Ohms :wink:

Voltage on the middle Pin of the Trimmer should be something between 0,5V and 1,5V can you confirm this?
If so, this seems not to be a mutable Instruments supplied Display, so try a higher R20.

Yep, the trimmer should be your focus at the moment.Check it is soldered at both ends.

i changed R20; but it didn’t resole my problem. it’s less bright, but the contrast is the same, so i cant separate easily the letter nd the case on the screen (i used 2.21K to see a changement. The problem come from the Trimpot, am i right ?

i desolded all the screen (worst job ever !), and changed the trimpot, now the contrast looks like to work , but i have another problem…

When i power on the shruthi, i have only the top line lighting and nothing more. i tried another screen and it was the same. ( i have already this problem on a shruthi 4PM, and i buy this one to try to resolve my porblem :/, bhaaaa i will become crazy…)

powered on the led 3 and 7 are lit, i can play some sound !

What i have broke again ?


R20 only affects backlight not contrast, correct. You shouldn’t have needed to desolder the LCD to touch up the soldering on the contrast trimmer. From the photo you posted earlier the characters were generating OK so it seemed the ATmega was alright then-could you post a photo of the current screen?

See here for your new Problem

ok, but i would to try without soldering the screen, because if i have again some problems with value floating, i could resold what i want. ! same for the sound, i resold a lot of point yesterday, and when i played some sound the volume is really low. i will record some sounds, but for me it don’t look like distorted.

i do it tonight ! Bye

If you are shure all connections are OK and Values still float then your PSU could be a bit to weak, especial when your Display draws more Power (this means is very bright). Check with a higher rated PSU. If it only floats at max setting then most likely your Pot is damaged.

i use a 500mA, i think it’s suffisant no ? ( the 4 PM worked with only 300mA).

i will redo some soldering tonight but i’m sure all looks like nice ! I already seen the screen changes when the value was not at max, so the pots should not be involved.

maybe i will try to just sold wire between the screen and the card, they could be desolded easily and i could change what i want !


Don’t trust the writing on the PSU, they lie sometimes.

sometimes := 95% of the time

Well 95% of statistics are made up :slight_smile:

But what I think they do is read the specification for the part and believe it, then write that on the case. It happens with bike lights too, they use a 200 lumen LED and so when they use three of them they say the light is 600 lumens. But in reality their circuitry and optics result in much less.

More or less the same with PSUs, they don’t test if the specification is feasible.

Ok, i changed my PSU by something more powerfull, but same problems.

I finaly resold the screen, but again the same blank caracters on the first line… so i have to chack the AVR, but what is it ?

i think i have to desold again the lcd… but i will finish by kill the pcb like that… :confused:

ok i would to change the MCU (the silver oblong 20 MHz crystal); but now nothing is working, no led and and no screen… i killed it ? … :frowning:

AVR is the big chip with 40 pins-thats also called the MCU (MicroController Unit). The crystal is essential for everything else to work and should not have been your first suspect, but is a cheap part to replace if you have damaged it.

If all else is OK the Shruthi should work perfectly without a display-buttons and LEDs will respond, and notes will sound via MIDI. Might be worth considering putting your LCD in a socket while you work on it or even leave the display off until you are sure the rest of it works. Doublecheck your soldering, clean up any solder bridges and go from there.

No offence intended but it sounds like you might be causing things to go wrong more than you are fixing them at this point. Take a deep breath and work slowly and calmly-you’ll get there!

PS Others have recommended this for socketing displays http://www.mouser.com/Search/ProductDetail.aspx?R=929870-01-16-RAvirtualkey51750000virtualkey517-929870-01-16-RA
I’m not sure what the Reichelt equivalent would be…

you are totally right, and i’m not offenced at all :slight_smile:

Everytime i try to resolve a problems, it’s worst after, I
don’t understand, the shruthi was working perfectly without the screen, and after solder it, nothing is working now, i will try to desold (again) the screen tonight, but i’m afraid to destroy the pcb…

Normally if i desoldthe , everything must work, like before… i will give you some news asap.