Abyss
- Thread starter servusjon
- Start date
chongmagic
Well-known member
Have you verified that the transistors are firmly in the sockets and that they are showing a voltage?
Have you measured the voltages on the ICs? Does the LED get brighter when you turn the intensity pot?
Have you measured the voltages on the ICs? Does the LED get brighter when you turn the intensity pot?
Chuck D. Bones
Circuit Wizard
I suggest that you touch-up your solder joints. I see a few cold ones. How about the Voice pot? Does that influence LED brightness?
Your yellow LED not flashing is probably just a symptom, and not the problem. There is a part of the circuit that has a varying voltage that not only makes the LED brighter and dimmer, but controls the changes in the sounds that you want to hear in the effect.
While having a sound play through your pedal, try shining a flashlight on the LED and photoresistors that surround it. Move the flashlight back and forth over them and see if you hear any phasing in the sound. If you do, it means that your problem may just be in the part of the circuit that makes the LED flash.
If shining the flashlight back and forth over the LED and photoresistors does not change the sound you are hearing, it means you may also have problems in other parts of the circuit.
While having a sound play through your pedal, try shining a flashlight on the LED and photoresistors that surround it. Move the flashlight back and forth over them and see if you hear any phasing in the sound. If you do, it means that your problem may just be in the part of the circuit that makes the LED flash.
If shining the flashlight back and forth over the LED and photoresistors does not change the sound you are hearing, it means you may also have problems in other parts of the circuit.
Chuck D. Bones
Circuit Wizard
Try this: connect the - lead of your DVM to ground on one of the 1/4" jacks. Set Speed & Intensity to 0. Set Voice to 5. Measure Vcc (pin 8 of either IC), verify it's +9V. If that's good, measure the base & collector voltages on Q1 & Q2 and report the results. If the oscillator is running, then Q1's collector voltage will wander around slowly.
if you like the way it works right now you do not need to change it. the trimmers adjust for the difference in how you place the photoresistors. no harm in trying them the other way if you want to, especially if you can just adjust them by carefully bending them.
Hello, new to DIY here and have the same problem as servusjon. Didn't know if should have created a new thread or not.
I have no short issues with the pots
I did some tests as mentioned above and here are my results:
Q1 Collector varies from roughly 0.54 - 3.0V - Base Voltage is 0.60V
Q2 has NO VOLTAGE anywhere
TL072 Pin 8 has voltage of 7.25V
TL074 has voltage on Pin 8 of 3.6V
I get sound and if I wave my hand over the LED area I get the warble effect but the LED is not lighting up. Obviously Q2 with no power is a problem, how do I trouble shoot this further?
Thank you
I have no short issues with the pots
I did some tests as mentioned above and here are my results:
Q1 Collector varies from roughly 0.54 - 3.0V - Base Voltage is 0.60V
Q2 has NO VOLTAGE anywhere
TL072 Pin 8 has voltage of 7.25V
TL074 has voltage on Pin 8 of 3.6V
I get sound and if I wave my hand over the LED area I get the warble effect but the LED is not lighting up. Obviously Q2 with no power is a problem, how do I trouble shoot this further?
Thank you
use the circuit diagram to find the parts that connect to Q2. use your DMM to check for continuity between those parts and the associated pins for Q2. if you find the parts that should be connected but are not, one is either not soldered in properly or there is a break in the trace between them on the PCB. you can figure that out after you find the specific connections on the PCB that are not properly connected.
Thanks zgrav, I did just that and found a total amateur mistake! I put the LED in backwards! 
Overall it was a good learning experience though and taught me how to troubleshoot. I did notice when I shut the pedal off the LED still flashes. Is this normal? Thanks for your help.
Overall it was a good learning experience though and taught me how to troubleshoot. I did notice when I shut the pedal off the LED still flashes. Is this normal? Thanks for your help.
