Duophase LED Problem

[tjazz]

I've been working on the Douphase project and I've run into a problem. One of the Leds is not turning on. It was turning on before but now it is not. The rest of the pedal works fine just this LED. Any help is greatly appreciated.

 

[Nostradoomus]

See if cleaning your board off with a toothbrush and some isopropyl alcohol does anything for you. There’s a lotta crud on there and a little bit of metal somewhere is all it takes to short something out!

 

[tjazz]

Tried cleaning off the board but it didn't change anything. Not sure where to go from here

 

[twebb6778]

Try using a DMM to see if the LED is still functional. It might have died for some reason.

If it's dead, replace it. If it's working, check you're voltages on TL072 in IC5A (particularly pin 1) and Q1A, these are the components controlling voltage to that LED.

 

[tjazz]

On Q1A there is no voltage on one of the legs. Does that mean that the transistor is dead? The other two legs have voltages of 8.3V and 8.95V. Tried switching the two transistors and the other lit the led but much fainter on this this side than the other. Pin 1 of IC5A is 0.2V

 

[Chas Grant]

Did you turn the depth knob A up, and have you tried adjusting TR1A? Both of these can affect the brightness of the LED.

 

[tjazz]

I tried adjusting TR1A and the depth knob as well. The LED has now stopped working even with both transistors. Not sure if there is a defective part or where else to test for signal failure

 

[Chas Grant]

Check and post voltages of IC5.1A pins 1, 2, and 3 to start.

 

[tjazz]

IC5 Pin 1 6.69V Pin 2 0V Pin 3 5.74V

 

[tjazz]

Update: One of the transistors is dead. Going to have to replace it. Also, the one of the LEDs is on but does not flash even when the rate is on. Not sure where the problem is.

 

[Chas Grant]

Yep it looks like Q!A is not conducting. Tackle that first then go after the other LED

 

[tjazz]

Replaced the transistor and one of the diodes. Works now!

 

[twebb6778]

Fantastic, glad you managed to get it working! This is a great reminder of how important the schematic can be when troubleshooting.