Aion FX Luna - worked fine, now it hums and oscillates

[BrenSabre79]

Hello. First time here so go easy on me please! :-)

1.What does it do, not do, and sound like?
This is a tremolo pedal. It worked fine in the blank box. I removed it from the box to apply decal and when i put it back together and switched it on the Rate LED (which should always be pulsing when there's power) flashed once and went dead.
I removed the LED from the circuit and tested it - it works fine. I put a new LED in anyway, that tested fine until I wired it in to the circuit and it doesn't work either.
Furthermore, there is no signal when the pedal is active, just a hum and some oscillation when I touch the Rate pot. the hum reduces considerably if I turn the Depth control down to zero.
I have reconnected all of the wires that link the main circuitboard to the LED/footswitch board.
All components seem to be as they should be - as I said i only removed the circuitboard to apply a decal and put it straight back. So I'm not sure if something has shorted and blown, or if I'm missing something. I'm not really sure what to look for now.
Any ideas most appreciated.
Thanks

2.Name of the circuit = Aion FX Luna
3.Source of the circuit (URL of schematic or project) = https://aionfx.com/project/luna-optical-tremolo/
4.Any modifications to the circuit? N
5.Any parts substitutions? N
6.Positive ground to negative ground conversion? N
7.What is the out of circuit battery voltage? =8.4V
Voltage at the circuit board end of the red battery lead = 8.03
Voltage at the circuit board end of the black battery lead = 8.01

IC1 TL072:

1: 3.87v
2: 3.87v
3: 3.79v
4: 0.00v
8: 7.73v
7: 3.86v
6: 3.86v
5: 3.70v

IC2 TL022:

1: 3.68v
2: 3.66v
3: 3.55v
4: 0.00v
8: 7.75v
7: 3.53v
6: 3.53v
5: 3.65v

Edited pin number to correct designation (thanks ElectricDruid!)

[ElectricDruid]

Welcome Bren!

I think you've got a short somewhere. That's why it was working ok at first, and then when you put it back together something got shorted to something else. Check nothing on the board or the external wiring can short onto enclosure. Can the backs of the pots short on the PCB? Are they well insulated? Could your Rate LED wiring be wrong? You said it was ok before you added that. Something is dragging the battery voltage down fairly heavily - that could be an LED, maybe. Maybe.

Also I think your IC numbering is wrong. The correct pin numbering starts at the top left (where there's a dot or a notch) and goes around anti-clockwise. It looks to me like you came top-down on the left (correct) but then came top-down on the right (not correct). You should have carried on around from pin 4 at the bottom to pin 5 on the other side at the bottom, and then up the right hand side.

The good news is that the voltages on the chips look fine, so I don't think that's a problem! Only the numbering is wonky!

HTH,
Tom

[BrenSabre79]

Hey thanks for the reply.

The problem started with the original LED in - I only started there as it was a visual indicator of a problem and testing the LED in situ returned NaN.

It is also exactly the same out of the enclosure too.
So whatever happened seems to be permanent. And seems to be making the LED non-functional while it is in the circuit.
Thanks

[ElectricDruid]

So tell us more about it.

Do you get clean signal when it's bypassed?

It *sounds* like the LFO isn't working. One thing you could try as a quick test is to swap the two chips over. The TL022 is the better choice for the LFO (lower current to try to reduce ticking) but the TL072 will work, so if that made the Rate LED start up, you'd have proved the TL022 chip was dead. If it makes no odds, we're probably looking for a fault elsewhere in the LFO circuit.

[BrenSabre79]

Hey thanks for your help.

Signal is fine when bypassed.

When activated it hums with a fast almost ticking oscillation - the speed of which is not at all affected by the rate control. but the spacing control increases the intensity of the oscillating. The hum reduces significantly when the depth control is turned right down.

I swapped the chips. It made no difference to the rate LED, so I have swapped them back. It seems like the chips are fine so I should probably test the LFO circuit components next.

Thank you!

[antonis]

Check C9 & C10 at first 'cause hum is indused somehow..

[BrenSabre79]

Update: Thanks for help so far.
Chips and capacitors C9 and C10 seem to be working fine.

Good news: I managed to get the LED working (sort of) and signal to come through when active. No hum, no oscillation. It's the same LED, so whatever was making it go dead is not anymore. Basically, i replaced all the wires linking the two boards.

Bad news: It doesn't actually tremolo. And the Rate LED is constantly lit.
When the pedal is active, the depth control basically attenuates the entire signal as you turn it up. So it's either no tremolo (depth down to 0) with signal. Or no signal at all (depth to 100%).

I replaced the TL072 - and now the depth control has no effect at all. So I get clean signal basically, just amplified/attenuated slightly by the volume control.

Any help appreciated, I'm about ready to throw the whole thing in the bin!
Cheers

[Carlinb17]

so I had an LED issue with this circuit when I built it a couple of month ago. It was completely my fault and my issue revolved around the forward voltage of the LED. I was using a UV 5mm LED for the rate side. I found that when I messed with the rate and depth the light would actually dim to the point of going out and there was a hum associated with this. The forward voltage for the UV LED was around 3.5. This clearly was too high. I ended up with an orange one with a forward voltage of 1.9 and the hum went away and the light was a constant brightness.

Not sure if this is something associated with yours it seems it could be. I'm certainly not going to pretend I know exactly the reason for the issue other than the led is connected two the two pots and not isolated. Someone with far more knowledge can let explain that part. Just a thought swap out the led for a red diffused one with a nice low forward voltage...?