Only LED 1 lights up, buttons do nothing


I just assembled my first Shruthi-1.
I got the readings on the power supply right but when I power up the complete unit only LED 1 lights up and buttons do nothing.

Does anyone know what might be wrong?


Check all the chips are inserted into the sockets the right way. Check for bent legs, then if those are okay start looking for bad joints.

I took all the chips out of their sockets and put them back in, but they looked right to begin with.

When I put the unit back together I didn’t get any lights on at all, which feels kind of weird to me.

My joints aren’t really that good, but I don’t see any that are obviously bad.

Have you swapped the 165 and 595? are there oriented correctly? Is the MCU inserted correctly?

We have power back, but still only LED1.

165 and 595 seem to be correct - 165 in IC2 and 595 in IC3, oriented so the notches line up with the ones on the PCB. Ditto MCU (that’s the big one in IC1, right?)

I’m having similar problems w/ my control board right now too. I didn’t bother to socket the 165 so I pulled it out (in retrospect, it might not have even been the problem…) to replace it with a socket, and pulled up 3 solder pads. Oops.

Tried with a different power adapter this morning.
Both boards still power up, but no LEDS light up with the new adapter.
When I switch back to the other one LED1 lights up again.

I get similar readings from the test points across the filter board as before.


Is the LCD backlight on?

I just tried attaching the LCD and the backlight is on.
It does not display any information though.

If you turn the trimmer contrast, do you see a row filled with white squares?

No, the LCD stays empty and I cannot see anything happening while adjusting the contrast.

What is the voltage on the middle pin of the contrast trimmer?

There seems to be too many different problems here! Even if the MCU is not working (which seems to be the case here as you can’t see the LEDs light up), you should at least see something on the LCD module when the contrast is correctly set…

I get 2.69V on the middle pin of the trimmer.

Aww damn, I was hoping to get it right the first time…
Are there there any voltages I can test to locate the problem with the MCU?

Then the trimmer is not correctly set. The LCD text shows up with values less than 1.5V.

You cannot troubleshoot MCU problems with a multimeter - besides checking that pins 30 and 10 of the MCU are at +5V.

Even if the MCU is getting power, it won’t behave well if the things that are supposed to be connected to it aren’t well connected.

Alright, the middle pin of the contrast trimmer is now at 1V but still nothing on the LCD except for the backlight.
Seems that the MCU is getting power at least.

Thanks for helping, by the way, I really hope we can get this to work!

Check the crystal and capacitors around it, check they are soldered well as it uses the external crystal usually.

They look pretty solid to me, but I’m going to do them again just to be sure.
The orientation of the quartz does not matter, does it?

No, the orientation of the quartz does not matter…

I soldered the quartz and all the capacitors on that side of the board again, but no luck.
Still only backlight on the LCD and sometimes light on LED1.

Would it help identify the problem if I posted a picture of my digital board?