Abyss

servusjon

Member
Built the Abyss, but for some reason the yellow LED doesn't flash but lights constantly fairly weak. Also I can hear no modulation. Any ideas?
 

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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?
 
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.
 
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.
 
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.

The sound reacts on the flashlight. The brighter it gets, the sound will disappear
 
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.

What is DVM?
 
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
 
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! :oops: 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.
 
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