Aion FX Luna pedal (Tremolo) / My recent build does not tremolo

[Carlos H.]

I finished building my Aion Luna Tremolo pedal a couple of days ago. Since then, I have been reading posts in this forum on debugging recommendations and what other problems people have had with this pedal build.

* Proyect build description:

https://aionfx.com/project/luna-optical-tremolo/

* Documentation (including schematics):

https://aionfx.com/app/files/docs/luna_kit_documentation.pdf

* What is it doing:

VOLUME and DEPTH knobs seem to cause the effect needed, i.e. with DEPTH all the way down, the pedal act as a boost controlled by VOLUME. Turning DEPTH up, attenuates the signal. However, SPACING and RATE knobs do not control the Tremolo effect. The red LED, which is supposed to follow the Tremolo sound, remains unchanged by the RATE knob, and this LED goes from off to solid red (no blinking in any position) once the the SPACING knob is tuned up beyond the 8:00 o'clock position (see attached pictures)

In summary, I have a Tremolo pedal that does not Trem.

* What is it supposed to do:

SPACING and RATE knobs are supposed to control the Trem wave shape and speed.

* What have I tried:

- Checked all resistor and capacitor values. See attached Table with Design values in the left column, and Measured values in the right column. A couple of resistors R10, R14, R15, R18, R19 seem way off, perhaps because I measured them in circuit.
- Made sure capacitor polarities are OK and that no capacitor is open or shorted
- Checked diods polarity and bias,
- Checked transistor bias, shorts, opens.
- Checked Vactrol optocoupler resistance on and off


I run out of ideas on things to check. That is why I am posting.

Any help will be most appreciated.

Thanks

Carlos H.

[antonis]

Hi & Welcome..

As some down-under guy always sez..

VOLTAGES,,!!

[Carlos H.]

Hi Antonis,

Thanks for the prompt reply.

I measured pretty much all resistor voltages (both terminals) and the IC pin voltages against ground.

Here is the schematics for reference. You can find the original documentation as indicated in my initial post.





I made all measurements keeping the knobs at 12 o'clock.





Here are all my measurements







For resistors, if only one value is reported, it's because the value was the same for both terminals.

Let me know if you want me to measure something else.


Thanks again for the help.

Carlos H.

[bartimaeus]

Hey Carlos, thanks for sharing so much info! That's usually the biggest problem with questions here, they don't say enough haha!

But to be honest, having the voltage at every single resistor is not so useful. And I'm a little confused, are those meant to be the voltages on each side of the resistor? Because that is not very helpful, it's impossible for us to know which side is which. Still, I appreciate you sharing so much!

Having the voltage at specific locations is much more important, such as the IC pins.

Speaking of which, it looks like your ICs are receiving the right voltages.

If I understand, you are hearing the dry signal, but there's no tremolo effect? That's a good sign at least. And it shows that Q1 and IC1 are working to buffer and amplify the signal.

IC2 is used for the LFO. If you have a constant ~4.5V on pins 1,2,3, 5, 6, and 7 IC2, that means the LFO is not oscillating.

We can hear this, because the depth control seems to be applying a virtual zero to the vactrol, attenuating the signal. that shows the vactrol is working too.

So the problem is likely around IC2. If you had an oscilloscope, you could probe to see if it's trying to oscillate, but that isn't necessary.

Can you confirm that R8 is 220k? From your photo, it looks like 20k.

I also notice that on the build guide, D3 is backwards. That would definitely break the oscillator. Makes me wonder if your PCB version has a typo and D3 should be flipped? Maybe you should email Aion about it.


The official image of the PCB also has that diode flipped, makes me wonder when they switched it:
https://aionfx.com/project/luna-optical-tremolo/#&gid=pswgname1&pid=1

By the way, I'd generally all more solder for the 3PDT pins. Those look fine, but they could go cold with consistent stomping if the connection is loose.

[duck_arse]

voltages. and welcome.

the voltage at pin 3 of the TL022 by my calcs should be restricted to a range of 1V5 to 6V7. yours is too high, as is the pin1 voltage. you might have a short or similar around that section of opamp. you could pull the 022 from its socket, power on and measure the empty socket pin voltages, which may shed light on things.

actually - pin 5 is also high, but pins 6 and 7 aren't following it as they should be. do you have any spare dual opamps handy you could try in that spot? at a pinch, swap the two IC's, and remeasure the voltages. pins 6 and 7 aren't following, but they are pulled by the DC connection to VA. aren't they?

[Carlos H.]

Hi Bartimaeus,

Thanks for the help. Regarding your questions/comments:

- Yes, the voltage measurements  (2 per resistor) correspond to each side of the resistors, unless I am reporting one, in which case there is no voltage drop detected. I was measuring following the schematics, and I thought all measurements would allow you to get an idea of voltages at every point in the diagram by looking at common voltages with adjacent components and ground point locations. I have very limited experience building electronics (this is my 3rd AION pedal, and the first to fail), so if this is not that useful, I will keep that in mind for next time. thanks   

- I can indeed hear the dry signal coming through, the volume knob works as intended, and the pedal amplifies the signal (increases volume beyond the input signal)

- At the moment, I have no access to an oscilloscope to check if the IC2 (TL022CP)
is oscillating or not. I only have a Klein Tools MM720 multimeter. The manual says you can measure frequency 0.001 Hz to 100 Hz for 2V to 220V RMS



with this multimeter I was not able to detect any oscillation.

- With 0%DEPTH control, the LED+ terminal of the Vactrol measures 1.712 V.
with 100% DEPTH control, the measurement is 1.685 V.

- R8 is indeed marked as 220k, but measures 150K, and R9 measures 115K

- Regarding D3 diod. I had the same question during the build (discrepancy between the diode image stamped on the PCB, and the building guide PCB drawing). After watching this build video https://youtu.be/_JjrbrLn0x4 , I concluded the PCB was correct, but now I am in doubt, after looking at the official PCB image you mentioned, and the schematics, where it's clear that the D3 cathode should be connected to the D2 anode. I will take the PCB out of the enclosure and check.

Thanks for the help. I will report back on what I find.

Carlos.

[Carlos H.]

Hi duck,

Thanks for the help. Here are the voltages of empty sockets for TL022CP

1.     2.002V
2.     1.886V
3.     3.093V
4.     0.4mV
5.     2.455V
6.     3.688V
7.     3.688V
8.     8.92V

Let me know if this makes sense.


Carlos.

[Carlos H.]

Hi Bartimaeus,


Just checked the connectivity of diode D3. It seems OK. My PCB is different from. the PCB image on the AION website but the diode image is correct in both. If you look closely, the official image has a connection between the D3 anode that the SYMMETRY pot. Same thing with mine if you look at the picture of my PCB.




I also checked the connectivity of D3 with adjacent components R10, TL022, D2,
and all seems to follow the schematics.

Any other ideas?


Thanks,


Carlos.

[Phend]

Novice here.
Pin 4 is to ground and should be 0v.

[antonis]

400μV shopuld be considered negligible but I'd like to have a measurement between In & Out sleeves..

[bartimaeus]

If the resistors and diodes are OK, then I am starting to wonder if the PCB has an issue.

Maybe you should double check that the PCB is ok. You can use the "continuity" setting on your meter to check if two points are connected. When you do that, make sure the pedal is unplugged.

Since depth is working, I am concerned about everything before Pin5 of IC2B.

For example, check if each side of C8 is actually connected to the smooth pot, if it is actually connected to C7, R12, etc.

It is rare, but sometimes the solder joints are fine, and the problem is the PCB itself has a bad connection.

You can also use continuity to double check the diodes. The anode of one diode should be connected to the cathode of the other. It the anodes or cathodes of either are connected together, then that is your issue.

[PRR]

....I only have a Klein Tools MM720 multimeter. The manual says you can measure frequency 0.001 Hz to 100 Hz for 2V to 220V RMS....

That's a very-OK tool.

We expect "a few volts" at around 10Hz. So that meter should read the trem signal. Unless the Hz function is overwhelmed by a few DC Volts. (I never tried than on my Klein; you'd think it would tolerate some DC?)

Another test is the DC Volts at various places around the oscillator (try both outputs of that dual op-amp). A needle-meter will "waggle" trying to indicate the wobbling voltage. Digital meters may "read crazy" 1V-3V-2V-5V.. because their read-cycle won't (usually) sync with the trem cycle.

But I see the others are ahead of me on the diagnosis and giving good tips.

[Carlos H.]

Hi Bartimaeus,

just finished checking connectivity between all components  R8, R9, SPACING_POT, IC2A, ...., SMOOTH_POT, IC2B. All seems in order. The only thing that threw me off was the apparent connectivity between terminals 1 and 3 of SMOOTH pot when I left the SPACING pot at 0% (i.e. zero resistance between terminal 2 and 1). This lead to only 2 Ohms between terminals 1 and 3 of SMOOTH pot (I honestly do not understand how this is possible, by looking at the schematics), as opposed to the 75 K measurement when I set SPACING pot to 50%. For a moment there I thought I had a short on either the SMOOTH pot or capacitor C8.

However, I have to say that I am trying to avoid desoldering, and because of it, I think,  I have not been able to measure capacitance of C4 and C9. For those, I keep getting a 0.000 reading followed by ----.

I throughly checked diodes D2 and D3 connectivity between them and the adjacent components R10, IC2A, SYMMETRY and RATE. They seem fine.

Is there any other thing you can think of before I start desoldering stuff off the PCB?


Thanks

Carlos.

[matopotato]

Hi Carlos H. and Welcome!

I wish I could be of more help to you, having built one myself. It was a while back, but I do not remember having any direct issues. Your diodes and mine concur. Electrolytes and Q as well.
Only thing I did differently was to socket the two LED R's and reversed the LED locations to get the on/off to the right on the pedal front instead. And might consider turning down the blue rate LED a bit.
Just don't give up, people in this forum are very very very helpful and keep trying things suggested and I hope it should bring you some very nice trem.

Btw, I have begun to check connectivity on each component's legs before cutting them. Between leg an next through-hole on the PCB. I think it has helped me at least although it is time consuming.

[Carlos H.]

Hi Matopotato,


Thanks for the suggestions.

After this experience, I have added a couple of steps to my building procedure.

1) Check PCB connectivity before adding any components
2) Check and measure each components before adding it to the PCB.


As you say, it takes time, but in the long run simplifies the debugging when the circuit does not end up working as intended

At this point, I am waiting for some components to arrive so I can  recreate the LFO circuit on a breadboard and check the opamps.

I will post on whatever I find.


Carlos

[bartimaeus]

just finished checking connectivity between all components  R8, R9, SPACING_POT, IC2A, ...., SMOOTH_POT, IC2B. All seems in order. The only thing that threw me off was the apparent connectivity between terminals 1 and 3 of SMOOTH pot when I left the SPACING pot at 0% (i.e. zero resistance between terminal 2 and 1). This lead to only 2 Ohms between terminals 1 and 3 of SMOOTH pot (I honestly do not understand how this is possible, by looking at the schematics), as opposed to the 75 K measurement when I set SPACING pot to 50%. For a moment there I thought I had a short on either the SMOOTH pot or capacitor C8.

rereading the thread, this is very odd. can you reproduce this measurement? if so, maybe the pot or C8 is bad, which is pretty rare but can happen.

[matopotato]

Hi Matopotato,


Thanks for the suggestions.

After this experience, I have added a couple of steps to my building procedure.

1) Check PCB connectivity before adding any components
2) Check and measure each components before adding it to the PCB.


As you say, it takes time, but in the long run simplifies the debugging when the circuit does not end up working as intended

At this point, I am waiting for some components to arrive so I can  recreate the LFO circuit on a breadboard and check the opamps.

I will post on whatever I find.


Carlos

No worries, if I can help in anyway, I'll be happy for you.
About 1). I thought that soldering and keeping the legs, then measure connectivity from leg to next point on the PCB will test several things in one.
Hopefully detect bad solders.
And also verifying the PCB tracing in the process.
And 2) I am also doing it since I sometimes get wrong components when buying a kit. And I can also confuse components and mix at times, so good strategies both.

I am guessing after a while it will be more of second nature and will not feel cumbersome or time consuming. But for me desoldering is riskier still, so anything I can do to minimize it is positive.

[idy]

And friendly advice: randomly desoldering components is likely to damage the PCB. Bad components are rarely the cause (except phony jfets and chips from bad sources... and a few other things...)

The LFO is not working and there are not that many components in it.

[duck_arse]

the published voltages for the R8/spacing/R9 don't work out right. if 220k and 150k, then spacing pot isn't 500k. if all correct resistance, then connection/s are bad somewhere along that string. I figure 6V7 at bottom of R8 and 1V5 at top of R9.

[Carlos H.]

just finished checking connectivity between all components  R8, R9, SPACING_POT, IC2A, ...., SMOOTH_POT, IC2B. All seems in order. The only thing that threw me off was the apparent connectivity between terminals 1 and 3 of SMOOTH pot when I left the SPACING pot at 0% (i.e. zero resistance between terminal 2 and 1). This lead to only 2 Ohms between terminals 1 and 3 of SMOOTH pot (I honestly do not understand how this is possible, by looking at the schematics), as opposed to the 75 K measurement when I set SPACING pot to 50%. For a moment there I thought I had a short on either the SMOOTH pot or capacitor C8.

rereading the thread, this is very odd. can you reproduce this measurement? if so, maybe the pot or C8 is bad, which is pretty rare but can happen.

Thanks for the suggestions Bartimaeus. I went back and I was able to reproduce my readings. That lead me to check connectivity between terminal 1 of SPACING pot and other components in the PCB. I found connectivity with terminal 3 of SMOOTH pot, which didn't make any sense, until I found a soldering bridge between one of the terminals of R9 and R11




I do not know how I let this pass while inspecting the populated PCB just before attaching the pots.

In any case, the pedal is working now.


Thank you and everyone for all the help and your suggestions. It's been a great learning experience.


Carlos H.