No light from LED 3, but Shruthi boots fine… Just a dead LED or a bigger problem…?
Do the other LEDs light up when you press the switches? Could just be the LED 3 resistor is not soldered right or the wrong value, or the LED is in backwards.
Could be a dead LED, swapped LED, a bad solder join on the corresponding current limiting resistor or 74hc595 pin.
So the right resistor is in, and the LED is soldered in the right way, for sure. All the others work fine, I can cycle through the menus with no problems and all other LED light up as they should. Maybe I’ll just remove the LED and try a new one.
Before pulling the LED I’d first check the all solder joints 595 > Rn > LED > ground.
Solder joints all looks good…
Like ByteFrenzy said, Check Pin 2 of IC3. then check the continuity from that to R4 then to LED3 then to ground.
You could cycle the lights round until LED3 is meant to be lit up and follow the voltage from the chip.
Would it be possible to connect VDC multimeter probes across the problem LED and see if the voltage alternates between zero and 4+V when you press the corresponding button repeatedly?
So I cycled to the point where LED 3 should be lit, and checked the voltage from pin2 to the LED. It just under 4v
Hi, that sounds like the power is coming from the chip ok. What voltage do you get across the 2 pins of the LED itself, if its above 2.5 volts and the LED is not lighting up I think there must be something wrong with the LED.
The only other thing would be if the resistor was too high a value, it would let a tiny amount of current flow which wouldn’t be enough to light up the LED.
Voltage across the pins of the LED is 0. But I know the resistor is the correct one. So I guess it’s a dead LED then?
@supercollider: hmm … if it’s 4V at pin 2 and 0V at the LED it looks like connectivity problem.
Hm, OK. I will keep looking, but to be honest, if the only side effect is an LED that doesn’t light up then I can live with it…
There needs to be a voltage across the LED for it to light up. So if there is 0 volts there must be a break in the circuit either to + or to ground. If you set your meter to resistance it should read 0 ohms from the negative leg of the LED to ground and the should read the value of the resistor from the positive leg of the LED to pin 2.
…with the board NOT powered please…