Strange LCD behaviour

Hi everyone,
so I have a Shruthi with strange LCD issues.
I have just built the control surface and when I power up all seems well. When I move the pots the last digits on the LCD are extremely flickery. Also the parameters jump around. For example I will try and alter the decay and the “release” text will flicker up, vou can still make out the decay text in the background. Sometimes changing a parameter it will jump to something else in a seemingly random fashion.
It also seems that pot 3 is doing 4’s job. 4 doesn’t do anything.
After adjusting a parameter the number will flicker for a bit then settle down and the screen will look fine.
Any ideas greatly appreciated!
I am using 9v 700ma
Cheers
Al

I have seen this behaviour once and I bet it’s the same problem. One or more of your caps have a bad solder joint.

Found this nice page when looking into it:
http://www.seattlerobotics.org/encoder/jun97/basics.html

Set all pots to zero and try using the Shruthi with the encoder only. If you don’t have any problem, it’s not a LCD problem.

To me it looks like a problem with the ATMega644’s ADC (flickering values), possible caused by a bad solder joint at the ADC input reference (C4). and possibly a short between the two ADC pins 3/4 ; or between the wiper pin of the 4th pots and one of the adjacent pins.

Things to check:

  • Voltage on the wiper pin of the 4 pots varies from 0 to 5V when the pot is turned from its minimum value to its maximum value.
  • The ground of the digital and analog boards are connected.
  • The +5V rail (measure at the left pin of each pot) is stable.

First off, thanks for the suggestions.
Did the LCD test you mentioned and it passed.
All pots are getting a consistent 5v at the right pin (while looking from the top)
However the voltages of the centre pin of the 4th pot jump around all over the place. So I checked the resistances of the pot. It seems to be a bad pot as the resistance is around 30meg. I’ll see if I can dig out a new one and report back…

YES! Sorry for the caps, but that seems to have fixed it. Dodgy pot. Haven’t seen to many of those! On with the testing…