Debugging and Aion FX Quadratron

[eahowe]

New to the forum and limited background in electronics. I have been building an Aion Fx Quaratron  (https://aionfx.com/app/files/docs/quadratron_documentation.pdf)  a Lovetone Doppleganger clone. I have built numerous amps and pedals, but I can't figure out what I've done wrong on this one. The green LED's do not light visibly (both red LEDs are fine). When I sweep a flashlight across the photoresistors I can hear the effect, so the circuit works except the green LED's won't drive the signal. I have checked all the resistors and get strange readings across R5, R8, R11, R14 (~ 57 K ohm, should be 220K - measure normally when removed from the board) and R16, R20 (~ 59 K ohm, should be 100K, also fine when not in the circuit). Voltage across the diodes D1: 9.47 V, 9.22V, D2: 1.26 V and null, D3: 8.67 V, 1.28 V D4: 0.26 V and null, D5 4.52 V and 0.27V. Not sure I am measuring those correctly? The op amp/ICs have some strange floating values, perhaps this is intended but my knowledge base is lacking. IC5 and IC6 pins 5 and 6 float between ~ 3 and 6 volts. Anyway. I have checked the soldered connections twice and verified values of all the parts. Can anyone tell me what I did wrong or what more information is helpful?

[Govmnt_Lacky]

Welcome to the forum!

First, I would recommend looking here: https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Next, I would recommend posting pictures of your build. https://www.diystompboxes.com/smfforum/index.php?topic=130157.0

You can also use other image hosting websites like Imagur.

Good luck!

[idy]

Welcome to the forum.
The good news is it passes audio and phases if you use a flashlight. So we know that IC 1-3 are OK.
IC 5 is the two LFOs. You would like to see the voltages going up and down there!
IC 4 buffers these two LFO signals.
ICs 6 buffers the two LFOs so they can provide the current to drive the LEDs, and one of these buffers can invert its signal for "anitphase" action.

You should expect resistors to read low in circuit, they often have other things in parallel. Taking them out is a classic way to damage a PCB! Been there...
I've made two of these, but on someone else's board...

[Govmnt_Lacky]

The green LED's do not light visibly (both red LEDs are fine).

Hmmm. Since the Red LEDs are tied directly to the same path as the Green LEDs (for each side independently) and the Red LEDs work, I would have to say your first look should be to make sure that the Green LEDs (all of them) were installed correctly.

[idy]

Yes, what Lacky said, I didn't think, do you mean the red LEDs are flashing with the LFO?

[eahowe]

Thank you all for replying! The red LEDs are power indicators only. There are two green LEDs that are visual indicators of LFO rate. Four Green LEDs in the box. All LEDs are installed correctly, I even replaced the ones that drive the photoresistors, just in case. I posted front and back to the Community folder, seemed like the easiest place. I may have buggered the board a bit in my efforts to resolder some of the connections, but I don't think it's too bad, just ugly. I am willing to scrap this and start over, but I don't like to give up until proven defeated.

[Govmnt_Lacky]

Any reason that you did not install C18? I see that C12, 14, and 16 have the option to substitute film caps but, C18 is necessary.

[eahowe]

C18 is in place at the upper right hand corner. C10 is left intentionally blank as I used film caps. I think you are seeing C10? The 0 looks like an 8 on the PCB?

[Govmnt_Lacky]

C18 is in place at the upper right hand corner. C10 is left intentionally blank as I used film caps. I think you are seeing C10? The 0 looks like an 8 on the PCB?

You are correct! Looks like it was C10 I was looking at.

You may want to power the pedal with both Rate pots at mid-range and measure to see if you get ANY DC voltage on the anodes of all the Green LEDs.

[duck_arse]

is there photos posted in this thread that I can't see? cause I can't see any. or maybe there's a link that I can't see.

[Govmnt_Lacky]

is there photos posted in this thread that I can't see? cause I can't see any. or maybe there's a link that I can't see.

LAYOUTS GALLERY > Recent photos

This is where I found them

[duck_arse]

yes, I went there, had no idea what I was looking for or at.

[eahowe]

Sorry about the picture mess. I have no idea what I'm doing and have never used a message board before. I am getting 2.7 V at the LFO LEDs and 1.7 V at the Modulation LEDs. I would expect these to change voltage with the LFO sweep?

[Govmnt_Lacky]

Sorry about the picture mess. I have no idea what I'm doing and have never used a message board before. I am getting 2.7 V at the LFO LEDs and 1.7 V at the Modulation LEDs. I would expect these to change voltage with the LFO sweep?

If you are getting voltage at the anode of the Green LEDs and you are still not seeing them light up at all (even dimly) then the issue must be the connection of the cathodes (to GND?)

Check your diodes D4 and D5 orientation and also check the operation of the LFO Cancel switch.

Make sure that the Span pots are turned up to max to ensure that the LEDs light up as bright as possible.

Need to get the LEDs lighting up and then work to see if there is an issue with the LFO.

[eahowe]

Okay.  Double checked all the diodes - correctly placed. With every pot dimed and all switches set to "off", the anode of LED 1 and LED 2 modulate between 4 and 5V. There is no visible illumination of the LEDs, confirmed in a black room. LED 3 and 4 have consistent measurements of 8.6 V at the anodes with the pots all dimed. How do I determine if the gnd is off at the cathodes? With power on and all pots dimed, the voltage at the cathode is 8.7 V across all 4 LEDs.

[Govmnt_Lacky]

After looking again at the pics, double check there are no shorts between the Anode and Cathode of ALL the Green LEDs.

Next, keep all pots dimed, select Dual LFO mode, and set LFO Cancel toggle to ON. Re-measure all Green LED anode voltages. According to what I see in the schematic, they should all read GND.

[duck_arse]

long gone are the days you could pick up a led and connect it with any confidence that the anvil or the body flat still denote the Kathode. (also - a square pad - what does that mean? anode? cathode? why not use the actual diode symbol?) who here hasn't been caught? if you have any spare of those exact green leds, get a 10k resistor and a 9V battery and jerry rig them together, see what combo of connections produce light.

looking closely at your board, there seems a few small patches around/near the leds with the appearance of bare copper, as tho the topcoat and the track had been scraped through. this would be a bad thing, but I  can't quite make it out.

[eahowe]

Lacky, With all pots dimed and LFO in cancel position, I still get a modulating voltage between 3-5 volts at the anode of LED 1 and 2, but 8.6 V at LED 3 and 4. 3.7 V at the HF LED and 1.6 V at the LF LED. With the LFO footswitch disengaged (LED Off), the anode of LED 1 and 2 stop modulating and drop to 0.8 V, LED 3 and 4 remain 8.6 V.
Idy, there is some scratch through at the board between the LF and HF Led leads, results of my overzealous attempt to prove to myself there was no short across the leads. I think it is fairly superficial, but not inconsequential, possibly.

[duck_arse]

Idy, there is some scratch through at the board between the LF and HF Led leads, results of my overzealous attempt to prove to myself there was no short across the leads. I think it is fairly superficial, but not inconsequential, possibly.

you need to check those traces aren't open circuit.

[eahowe]

This may be a problem, Duck, though probably not the original problem. As I have little experience with anything other than following directions, what is the best way to test if this has caused an open circuit?