Problems with Potentiometers 1 & 2 [solved]

Hi there!
I have just finished to assembly my first shruthi- SMR4-mkII, but i have a problem with the first two potentiometers.
when i try to modify value with potentiometer n°2, it doesn’t have any effect.
But when i move potentiometer n°1 value for parameter 1 (assigned to Potentiometer 1) and 2 (assigned to Potentiometer 2) are moving.

Can you help me and tell me where is my mistake.

thank you


Check pins 39 and 40 on the ATMEGA. You may have a short circuit there and some bad solder joints. Also check the legs aren’t folded under.

Looking at the ATMEGA from the top with the notch pointing upwards, pin 40 is the top pin on the right side, 39 below it. Pin numbers go anti-clockwise around the IC.

thank you, i remove the lcd screen and i try this

It could actually be the LCD touching the pins. So you might want to try putting some plastic (old credit card) between the LCD bezel tabs and the chip pads. Before you do anything more drastic.

thank you!
i have made the test with a credit card, but it’s the same problem, now i will remove the lcd screen

Again, before you remove the LCD (which will be hard work) Take out the ATMEGA and put a meter across pins 39 and 40, you will then know if you have a short.

using the multimeter and continuity test ?

i have no sound with the continuity test, so it must be ok.

I think he meant to check those pins to make sure they are properly inserted in the socket and not bent and folder under the chip. This happens sometimes if the pins aren’t straight to begin with…

Desoldering the LCD is going to be a huge pain in the ass. Do that LAST once you have ruled out everything else.

Have you checked for continuity between the pin 40 and the wiper (center pin) of pot 1 ; and between pin 39 and the wiper of pot 2?

What is the voltage on the middle pin of pot 1 when you move the pot from min to max?

the pins are properly installed, is that possible that my potentiometers are dead or something like that, because when i have mounted the shruhti, i have put the first two potentiometers on the wrong side of the mainboard, removed them and put them where they have to be.

thank you pitchenettes, no continuity between pin 39 and wiper of pot 2

Ok, so we have found the cause of the problem… pin 39 is left floating which means that it is picking up noise instead of the position of pot 2.

Check the soldering of pin 2 of the pot, or of pin39 of the MCU.

If you don’t want to remove the LCD, a very dirty hack would be to solder a piece of wire from pin 39 of the MCU to pin 2 of the pot - but check first that your solder points are OK…

thank you pitchenettes, you’re right i’have tried with a wire and it works, no i will repair the solder point from pin 39!

Thank you for your help!