Tiny flickering of all values

I bought an already assembled Shruthi a while ago and have been enjoying it tremendously since…but…I have an issue with the values of the parameters (all parameters) flickering (not all at the same time, mostly one at a time). I have read the troubleshooting page and saw that a weak power supply can cause this. So I’ve tried 4 different supplies delivering up to 600mA. Same story with all the supplies. So it seems the power supply is not the issue. The flickering is quite subtle - it’s like the controls can’t decide wether to stick with X or X+/-1 - as if the pots were too sensitive, so they needed to be tweaked ever so gently to stay at a certain value. What could possibly be causing this?

Maybe I should mention that my specific Shruthi has the IR3109 filter board and is equipped with an OLED display.

Any help much appreciated.

Make sure the correct filter board is selecting under settings. If its set to programmer, it will cause that erratic behavior.

Try and find a linear regulated PSU. A switch mode PSU can cause problems with sensitive kit.

Thanks for such fast answers

I’v checked the settings and they are alright: filter set to lpf and mode to 4 cv in. I’m using a non-switching 500mA supply now.

I noticed something tonight: After changing a value in one page (e.g. cutoff in the filter page) and that value starts flickering, if I then switch to another parameter page and then back to the filter page again the flickering is gone and the value doesn’t change until I turn the pot again. Strange.

Maybe it’s an issue with the 2 capacitors on top of the 644p on the control board? The problem is, if so, it won’t be easy to fix since the solder joints are hidden under the screen.

I have seen two causes of this problem:

  • Bad power supply.
  • Weak connection on the ATMega644p socket (this sometimes happen with the ZIF socket in which I have inserted more than 2000 chips for flashing). Check that the chip is firmly inserted in the socket.

I’ve also had some flickering value and intermittent MIDI IN. With the precious pichenettes’ advice and help, I’ve ended up changing my ATMega chip because the first I’ve used had too many bended pins (thanks to the french postal services … grrrrr ! ), even if ive tried to carefully bend them back in the right position.
So check if the ATMega is well clipped on his socket.

Hédi K.

So the most likely cause this far seems to be a bad connection of the ATmega644p chip. I guess I should check the IC-socket for cold joints as well as check that the chip is inserted firmly in the socket, right? I’m a complete noob when it comes to these things (that’s why I bought an assembled unit, although I would like to learn this stuff eventually).

Any thoughts on why the flickering stops when I change page? (It starts again when I turn a pot, but then all I have to do to make it stop is to switch parameter page again).

There’s an OS feature that make the pots less sensitive when switching pages; and which increase their sensitivity once they are touched - to prevent accidental parameter “jumps” when switching pages.

I had something similar to this happen once, so I resoldered a couple of the bypass capacitors. Don’t know if they were the cause, but it helped. Could have been the power supply I guess.

I have seen similar things on Prototypes i did (NO - NO PROGRAMMER) with OLED Displays, solved by adding some buffer Caps (say 100N ceramic + 100µ Electrolytic) directly to the Displays Pins

I will open up the Shruthi tonight to have a look at the ATmega chip and the IC-socket. Hope I can solve it there.

@pichenettes: Would it be possible for me to change the sensitivity of the knobs without rewriting part of the OS (which I can’t)?

@fcd72: Was the problem with the display of the values - I mean, did the actual values not change, only the values on screen? I’m asking this because I don’t understand how soldering caps to the display pins solved the issue.

This is an awesome forum by the way, with so many nice people helping out. Thanks!

@Modularmind
It seems that at least the OLEDs i used lead to some fluctuations on the Power Rails, i replaced them with a standard LCD and everything went fine, so i soldered the Caps and the problem got away. Your CPU is buffered with the decoupling Caps, your Pots are not (they are directly attached to the Rails) so when the Rails fluctuate your CPU might have more stable power for internal reference hence the Values flicker.

So would it be better to decouple the OLED power pins or do it at the pots?

Best would be a Display that doesnt stry nasty transients to the Rails… from an engineering point i would say kill the problem where its origin is, so decouple the LCD

> @pichenettes: Would it be possible for me to change the sensitivity of the knobs without rewriting part of the OS (which I can’t)?

Yes, I could compile a version of the firmware with less sensitive pots, but then values would move only by multiples of 2 on some settings and it would feel quite step-y.

Would it be easier to change the display to a regular LCD or to decouple the OLED (from a soldering-noobs perspective)?

@fcd72: If I need to do this to fix the problem, would it be too much to ask if you could guide me through the process? I only have a very rudimentary knowledge of electronics.

Shure - its dead easy, first get a 470n ceramic cap or something in that range from a local dealer. if you are in Germany ill send you one.

@fcd72: Thanks! I’ll checkthe ATmega chip possiblity first. If that don’t give any result I’ll get at cap for the display (I’m in sweden).

@pichenettes: Very kind of you to offer this. But I’d rather not have the stepping if I can avoid it, so I will try the other routes first.

@Modularmind
If you are somewhere where its complicated getting a Cap jojjelito is the one to ask - he will shurely help you with an InnerswedishCapacitorTransmission™