Aion L5 Preamp (9VDC Version) Troubleshooting (voltage drop issue)

[noisegrrrl]

Hi!
I had just finished building my Aion L5 Preamp (https://aionfx.com/project/l5-preamp/) and was beginning the calibration phase but I was reading nowhere near 4.4V when trying to set the distorsion trimmer.
I tried plugin it directly into an amp to see if I was getting sound and that at least seemed to work, however: The sound is distorted no matter what and there is a constant background ringing that is quite loud (frequency around 3.2kHz), I also need to max out both master and volume on it and even then it's not as loud as the amp with the pedal bypassed. So this sounded like a headroom problem of sorts.
I started measuring voltages on the differents ICs (https://docs.google.com/spreadsheets/d/1k03_BPjMnBZT2fpMgZ-sIpijophlDjRzGhcjGetKSRQ/edit?usp=sharing) and it seems like the pedal was not getting enough power (VA = 1.8V)
I have tried multiple power supplies but the problem persisted.
I tried tinkering a bit more what I have noticed is that if I don't connect the power/switch board to the main pcb VA and -VA are 15V and -15V as intended, but as soon as the main pcb is connected the voltage drops to 1.8V and -1.8V.
I don't know if this is related but L1 tends to heat quite a bit as well.
The voltage only drops when the left part (PCB IN / 15V / GRND / PCB OUT) of the power/switch pcb is connected to the main pcb, the right part (15V / A3 / A2 / A1/) connection doesn't seem to impact the voltage.
I'm not sure how to fix this, it doesn't look like there are any solder connections shorted.

[ElectricDruid]

I tried tinkering a bit more what I have noticed is that if I don't connect the power/switch board to the main pcb VA and -VA are 15V and -15V as intended, but as soon as the main pcb is connected the voltage drops to 1.8V and -1.8V.

This is a MASSIVE clue and pretty definitive!

I don't know if this is related but L1 tends to heat quite a bit as well.

Yep, probably related. It's all looking like a big short is killing the power.

The voltage only drops when the left part (PCB IN / 15V / GRND / PCB OUT) of the power/switch pcb is connected to the main pcb, the right part (15V / A3 / A2 / A1/) connection doesn't seem to impact the voltage.
I'm not sure how to fix this, it doesn't look like there are any solder connections shorted.

It certainly *sounds* like there's a solder connection shorted somewheere, and if you show us the other side of the board, perhaps we can help you look for it!
We're going to need to see the wiring and connections on that power/switch board in particular, since that seems to be what's causing the problem.

HTH!

[noisegrrrl]

Hi, thank you for the help.
I took a few more pictures:

Here is the "power/switch" board:









Here is the main one:











And this is what I use to connect the two:



Let me know if you need a picture of something specific/if I should test something in particular.

[antonis]

Hi & Welcome..

[noisegrrrl]

Hi & Welcome..

That's flux or something else, not solder, and I just checked with a multimeter, there is no short there, I think that's a reflection, I reflowed the solder on this board anyway just in case (it's also the switch and if you look at the orientation, that path is supposed to be closed when the switch is engaged/disengaged at some point).
I'm thinking the short would most likely be on the main board since the voltage doesn't start dropping until it's connected to it.

[duck_arse]

pull those two jumper/linkers from the main board, and measure the resistance between the header pins on the board. check between GND and -15V and +15V pins especially.

also welcome.

[Frank_NH]

I built the old version of the Aion L5 preamp (it's a ** great preamp ** BTW) and like you encountered a voltage problem after firing it up for the first time.  At first I thought it was the voltage regulators and replaced one of them to no avail.  Then after some very close inspection of the entire board I found it!  It was the tiniest spec of solder bridging two pins on one of my IC sockets!  After fixing that, it worked fine with no issues (I still use it nearly every day).

I would inspect all of the socket pins for a solder bridge - I think that's where the problem most likely is.  Also, from your photos I couldn't tell if your right angle pots were protected from the PCB - if not get some plastic 16mm pot housing protectors (or you can just glue some foam strips to the bottom of the pots).  Go luck!

[Edit - I think I saw some pot protectors in one of your photos...]

[noisegrrrl]

pull those two jumper/linkers from the main board, and measure the resistance between the header pins on the board. check between GND and -15V and +15V pins especially.

also welcome.

On the main board:
+15V - GND -> 8,27kohm
+15V - -15V -> 5,7kohm
-15V - GND -> 7kohm

+15V - A3 -> 34kohm
+15V - A2 -> 5,3Mohm
+15V - A1 -> 54kohm 

I'm getting the same order of magnitude between GND,-15V and those 3 points.
PCB IN and OUT are in the Mohm range with all the other points so I'm guessing everything is in order for those two.

on the power/footswitch board:

+15V - -15V -> 32,8kohm
-15V - GND -> 3,4Mohm
+15V - GND -> 3,8Mohm

The others wouldn't give a reading except for A2 - A3 where there was continuity but that's because it's the channel selection, if I engage the switch, I get continuity between A1 - A2

I built the old version of the Aion L5 preamp (it's a ** great preamp ** BTW) and like you encountered a voltage problem after firing it up for the first time.  At first I thought it was the voltage regulators and replaced one of them to no avail.  Then after some very close inspection of the entire board I found it!  It was the tiniest spec of solder bridging two pins on one of my IC sockets!  After fixing that, it worked fine with no issues (I still use it nearly every day).

I would inspect all of the socket pins for a solder bridge - I think that's where the problem most likely is.  Also, from your photos I couldn't tell if your right angle pots were protected from the PCB - if not get some plastic 16mm pot housing protectors (or you can just glue some foam strips to the bottom of the pots).  Go luck!

[Edit - I think I saw some pot protectors in one of your photos...]

They are protected, it's not a full housing protector but there are rubberish pads glued to the bottoms of the pots, I'll recheck the ic pads

EDIT: I've checked the IC pads with the ICs removed, except for the few ones that are meant to be connected, there's no continuity between them

[Rob Strand]

Check your electrolytic caps are around the right way.   All of them but especially those on the power rails.
From your pics they look OK to me.

[noisegrrrl]

Check your electrolytic caps are around the right way.   All of them but especially those on the power rails.
From your pics they look OK to me.

They are all the right way yes, I've started desoldering them one by one to test them and inspect them, so far C42, C44, C46 and C47 are ok as far as I can tell (multimeter + visual inspection)

[Rob Strand]

Try pulling out IC4 and IC5 and see if the supply voltage restores to normal.

What can happen is IC4 and/or IC5 could oscillate and cause the unit to pull high current.

You could start judiciously pulling other devices.   If the supply voltage restores to normal you need to back pedal a bit to work out why.

- The simplest answer is the last IC your pulled was the cause but not guaranteed.

- It could be the last IC you pulled is part of a bigger issue that needs investigating.

- It could be pulling the last IC has dropped the current draw to a point that that the regulator starts working.   The last IC has nothing to do with the actual problem.   The remaning stuff is likely to be problematic.


Don't pull IC9 or IC10 unless you have isolated the problem to that area.

[noisegrrrl]

Check your electrolytic caps are around the right way.   All of them but especially those on the power rails.
From your pics they look OK to me.

Ok, I've desoldered and tested all the electrolytic capacitor on the main board, all of them are ok as far as I can tell (correct value and don't seem damaged).

Try pulling out IC4 and IC5 and see if the supply voltage restores to normal.

What can happen is IC4 and/or IC5 could oscillate and cause the unit to pull high current.

You could start judiciously pulling other devices.   If the supply voltage restores to normal you need to back pedal a bit to work out why.

- The simplest answer is the last IC your pulled was the cause but not guaranteed.

- It could be the last IC you pulled is part of a bigger issue that needs investigating.

- It could be pulling the last IC has dropped the current draw to a point that that the regulator starts working.   The last IC has nothing to do with the actual problem.   The remaning stuff is likely to be problematic.


Don't pull IC9 or IC10 unless you have isolated the problem to that area.

As I've started pulling ICs starting with 4 and 5, the voltage augmented a little each time I pulled one, however, with all ICs pulled, I only get up to +/-11V, I'm not sure what that means but I'm guessing I can rule out a fault of the ICs?


EDIT: L1 really gets hot with time, could it be an issue with this? Also to note, there is a constant noise coming from one of the component, the noise started changing frequency when pulling ICs, I think it might be coming from the DC/DC Converter, when only the power board is plugged however, there is no noise

[Rob Strand]

As I've started pulling ICs starting with 4 and 5, the voltage augmented a little each time I pulled one, however, with all ICs pulled, I only get up to +/-11V, I'm not sure what that means but I'm guessing I can rule out a fault of the ICs?


EDIT: L1 really gets hot with time, could it be an issue with this? Also to note, there is a constant noise coming from one of the component, the noise started changing frequency when pulling ICs, I think it might be coming from the DC/DC Converter, when only the power board is plugged however, there is no noise

As soon as I read 11V, I started to think the inductors DC resistance then in the next paragraph you pretty much answered it!

I'm pretty sure you have the wrong inductors in there (it could also be a fault).

With the power off measure the DC resistance across the inductors.

If you can try to read the labeling on the inductors.  Maybe you have 10mH (milli henry) and not 10uH (micro henry).   Even if you get the  uH/mH correct you need to make some effort with the inductor selection.
If you can post a link to the inductors you bought.

The input inductor L1 is going to carry a lot more current than the output inductors.  Also the DC resistance
of L1 is more important than that of L2 and L3.   Of course if you have a good inductors the
same inductor can be used in all three positions.
I found a pic of your inductors from the images you posted earlier.  If they are 10uH and not 10mH there's a good chance that size inductor should be good enough.

[noisegrrrl]

As soon as I read 11V, I started to think the inductors DC resistance then in the next paragraph you pretty much answered it!

I'm pretty sure you have the wrong inductors in there (it could also be a fault).

With the power off measure the DC resistance across the inductors.

If you can try to read the labeling on the inductors.  Maybe you have 10mH (milli henry) and not 10uH (micro henry).   Even if you get the  uH/mH correct you need to make some effort with the inductor selection.
If you can post a link to the inductors you bought.

The input inductor L1 is going to carry a lot more current than the output inductors.  Also the DC resistance
of L1 is more important than that of L2 and L3.   Of course if you have a good inductors the
same inductor can be used in all three positions.
I found a pic of your inductors from the images you posted earlier.  If they are 10uH and not 10mH there's a good chance that size inductor should be good enough.

They came with the kit from musikding, I'll write to Klaus tomorrow to check with him if he remembers what they were, I can't make sense of the markings on them.

[Rob Strand]

They came with the kit from musikding, I'll write to Klaus tomorrow to check with him if he remembers what they were, I can't make sense of the markings on them.

You should be able to read the markings on the side.   Maybe a number like 100.

There's a good chance they are correct.   What you could do is measure the current going into the circuit.

If your meter has a 10A range use that.   Your circuit will be drawing more than 200mA so don't use the 200mA range and sockets - it will just blow the fuse in the meter.

See,  except you want to set the meter to *DC* current,
https://ecampusontario.pressbooks.pub/app/uploads/sites/69/2018/03/1-5-multimeter.png

When you finish making  the measurement, make sure you swap the meter plugs back to the voltage terminals straight away.

[noisegrrrl]

They came with the kit from musikding, I'll write to Klaus tomorrow to check with him if he remembers what they were, I can't make sense of the markings on them.

You should be able to read the markings on the side.   Maybe a number like 100.

There's a good chance they are correct.   What you could do is measure the current going into the circuit.

If your meter has a 10A range use that.   Your circuit will be drawing more than 200mA so don't use the 200mA range and sockets - it will just blow the fuse in the meter.

See,  except you want to set the meter to *DC* current,
https://ecampusontario.pressbooks.pub/app/uploads/sites/69/2018/03/1-5-multimeter.png

When you finish making  the measurement, make sure you swap the meter plugs back to the voltage terminals straight away.

Should I keep one leg of it in the circuit then? And probe between the other leg and the circuit?


Here are the picture of the inductor:

[noisegrrrl]

I'm getting 0,095A without the ICs in and 0.080A with the ICs in measuring between the circuit and L1
I'm measuring 62,8ohm for L1 and about 59ohm for both L2 and L3

That seems pretty low for the current no?

[antonis]

So you have 15mA current draw with all chips ON..
That call's for less than a volt drop across L1..

[ElectricDruid]

I'm getting 0,095A without the ICs in and 0.080A with the ICs in measuring between the circuit and L1

Less current with the chips in than without? That seems odd.

That seems pretty low for the current no?

It's not a lot of current, but almost 100mA is fairly large in pedal terms. Back when I used to design pedals to run on a 9V battery, I was looking for <5mA current draw, ideally 2 or 3mA. Many old fuzzes are even less than that.

[noisegrrrl]

I'm getting 0,095A without the ICs in and 0.080A with the ICs in measuring between the circuit and L1

Less current with the chips in than without? That seems odd.

That was surprising to me as well, I redid a measurement just in case, this time once with only the power board and then with the main board connected, the value fluctuate a lot, one measurement will give me 0.060A on the power board alone then if I disconnect and reconnect my probes I read either 85mA or 63mA.
When the main board is connected I'm getting a consistent reading though of 73mA.
I'm thinking the 63mA might be the correct one.