Trouhbleshooting an Aion L5 Lab Series Preamp

[rmjlmartin]

 Hi everyone, and thanks in advance for your help.

I'm troubleshooting an Aion L5 Preamp for a friend, and I'm relatively new at pedal building and troubleshooting, so I'm bumping up against the limits of my skills.

First off, here's a link to Aion's page, which has a link to the build document- https://aionelectronics.com/project/l5-preamp/

My friend built this and was unable to get it to work, so he sent it to me. So I got it completely assembled. I found and repaired a power supply problem on it, and he originally had it wired so the yellow wire was connected between the footswitch boards, which was supposed to make so the channel indicator leds turn off when the pedal is in bypass, but the power led stayed on all the time, so I wired it to the ground pad so the channel leds will stay on all the time. I also added the ground wire for the output jack on the right so I could test it out of the enclosure.

Using an audio probe, I get the signal all the way through the circuit to the input (pin 2) of IC10. On the output (pin 6), I get no sound with the probe, unless I hit the strings pretty hard, and then I get a very fuzzy, splatty sound like the power supply is too low.

I found another post on here (https://www.diystompboxes.com/smfforum/index.php?topic=121736.0) where Kevin from Aion posted a link to his voltage test chart, which is here- https://docs.google.com/spreadsheets/d/1GbYmJUXo2WXESJkMD1xxxkrgvPOt8DurWDE5TvscMMk/edit?usp=sharing

I've tested the voltages , and everything seems to be correct, except the 2 CA3080 chips (IC10 and IC11) and the 2 2N5088 transistors associated with IC10 (QX1 and QX2). According to the test chart, the voltages should be-

IC10- (CA3080E)
1- 0
2- 0
3- 0
4- -15.2
5- -14.5
6- 0.9
7- 14.73
8- 0

IC11- (CA3080E)
1- 0
2- 0
3- 0
4- -15.2
5- -14.62
6- 0.23
7- 14.73
8- 0

QX1- (2N5088)
1- 0.4
2- 0.9
3- 14.66

QX2- (2N5088)
1- -0.22
2- 0.4
3- 13.21

The voltages that I have, measured with the negative lead on my multimeter on the center test point at the top right next to the power supply section, are-

IC10-
1- -14.69
2- 0
3- 0
4- -14.91
5- -14.65
6- 13.11
7- 15.1
8- 14.41

IC11-
1- -14.85
2- 0
3- 0
4- -14.92
5- -14.85
6- -2.06
7- 15.11
8- -0.73

QX1-
1- 12.63
2- 13.16
3- 15.02

QX2-
1- 11.98
2- 12.64
3- 12.26

I have more 2N5088 transistors on hand, and I've tried swapping them out (no change), and I've tried swapping IC10 and IC11 (also no change).

But since I know the CA3080 isn't just a standard op amp, and doesn't test the same, I'm a little at a loss of where to go from here. Do I likely just have 2 bad CA3080 chips? Or is there something else I should be looking at?

Again, thanks for taking the time to read this and especially for offering good advice!

[ahiddentableau]

First thing that jumped out at me was that Pin 8 on one of your 3080s (IC11) has full positive voltage.  According to the schematic and normal use of those chips, that should be no contact.  So that's the first thing I'd look at.  Solder bridge?  Something amiss in that area?

[rmjlmartin]

Thanks!

Yes, I wondered about that. Pins 1 and 8 of both CA3080s (IC10 and IC11) have voltage on them, but according to the schematic and datasheet, they shouldn't have anything connected to them.

I don't believe that there are any solder bridges, at least none my multimeter seems to be able to find. And I forgot to mention that the odd voltages are only present with the chips installed.

I posted this on DIYstompboxes, too, and someone there pointed that out, suggesting that the chips are defective or not genuine. I don't know where my friend sourced them, but they are Intersil brand. So maybe we just need to try another pair of chips?

[ahiddentableau]

If there's no voltage at all on pin 8 when you pull the IC then I totally agree with you: replacing the CA3080s with known genuine units is the next logical step.

I have some personal experience with fakes like you describe.  I got a few off ebay from China a few years ago and they were branded intersil and they were fake.  Really, really fake.

Small Bear just got a new shipment of 3080s in so sourcing real ones is easy enough.  Let us know how it works out.

[rmjlmartin]

Thanks!

Yes, I'll update when I know more. My friend who built it has more chips (hopefully from a different source) and is going to send them to me. But he's getting together a box of things to send me, and is very busy at work right now, so it may be a month or so until I get them.

But I will update when I get to try other chips.

[rmjlmartin]

Hi again. I'm finally back and updating this after getting the replacement chips from the friend who built the pedal.

I'm happy to report that the chips solved the problem. With the different chips, it seems to work as it should.

Thanks again to all of you who took the time to read this thread, especially the ones who offered to help a relative noob!

[francho]

rmljmartin Did you ever solved this issue? I am facing similar problems and my unit is bahaving the same way as yours.

[mauman]

rmljmartin Did you ever solved this issue? I am facing similar problems and my unit is bahaving the same way as yours.

He said his CA3080 chips were fake, and acquired some new ones from a reliable source, that fixed the problem.