Aion Theseus (KoT) issues

[RickMcCarthy]

Hey all,

First time poster/long time lurker. I built a handful of things over the years starting with Aron's hornet fuzz which I built into an old Stonco box (fellow electricians will know what that is). Each of these projects have been mostly successful, meaning that they would seldom fire up on the first go around but I could usually find a backwards cap or some other silly mistake that I made and get it going. This project perplexes me though.

To be clear, I built this from the PC board and not the kit with parts from Mouser and Small Bear - no substitutions. On first fire up I get a clean bypass signal but when I engage either side of the pedal it passes no signal with no noises. I dug into it and quickly noticed that I had no voltage on the "B" side (KoT yellow side). After a while I noticed a broken trace on the foot switch/LED board which leads to the VC pad. So, I installed a small wire jumper from the + pad of C22 to the VC pad on the board and EUREKA! We have a functioning "B" side!

Going back to the "A" side I noticed that I still had voltage but it seemed incorrect on IC1. From the build documents I should have:

IC1
Pin 1: 4.66v
Pin 2: 4.67v
Pin 3: 4.25v

Whereas, I read:

Pin 1: 8.67v
Pin 2: 2.68v
Pin 3: 2.66v

(Note that the build document readings are from a 9.7VDC power supply and mine is 9VDC on the dot).

So, I figured that maybe I had an open cap to ground or some other bad component. I even tried swapping the ICs to see if it was a bad chip but I get the same performance when I swap them. This is perplexing. Having the exact same circuit functioning on the board seems like it would be easy to troubleshoot, but I'm stumped. Does anyone have an idea as to where I should focus my attention? Any help would be greatly appreciated.

I tried to take a screenshot of the schematic and it came out blurry. It's in the PDF file located here:

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

[RickMcCarthy]

Apologies if I left some information out. I'll have some time to dig into it a little later today.

[ElectricDruid]

Welcome Rick, now you've stepped out of the shadows! 

What voltages do you get on the other pins of IC1, please? Especially pin5, since that's directly connected to Vb.

At first glance, it looks like something is throwing the Vb voltage out. There's lots of ways that could happen, but we'll get to that in a bit - first let's check those other pins for confirmation.

[antonis]

Welcome also..

Can't be sure but it seems to me that TONE pot(s) backplates might short ICs..

P.S.Also, many wiring solderings don't look clean..

[RickMcCarthy]

Thank for chiming in ElectricDruid and Antonis,

I did a fresh set of readings just now and here's what I've got:

IC1

Pin 1: 8.20v
Pin 2: 3.12v
Pin 3: 2.47v
Pin 4: 0v
Pin 5: 4.31v
Pin 6: 4.32v
Pin 7: 4.28v
Pin 8: 8.61v

... and the op amp from the functioning "B" side:

IC2

Pin 1: 4.25v
Pin 2: 4.28v
Pin 3: 4.27v
Pin 4: 0v
Pin 5: 3.97v
Pin 6: 4.36v
Pin 7: 4.35v
Pin 8: 8.55v

Supply voltage as measured: 9.02VDC

Pin 5 looks to be in the ballpark, ED. Odd that the other side is a touch low but functions.

You are correct Antonis, zooming in on those photos reveal not my finest hour with the soldering iron. I'm thinking that re-flowing the solder wouldn't be a bad idea.

Also, I do have a good deal of space from the rear of the tone pots to the rear of the board so I have been able to rule this out. Weird, though.

[RickMcCarthy]

So I reflowed solder in the joints but no luck.

Anyone have a sense why I'm getting weird voltages on IC1. This one has me befuddled.

Of course, enjoy your holiday weekend first, good people. 🍻

[antonis]

I'd pull IC1 out of its socket and get measurements on pins 1, 2 & 3..

[aion]

I would triple-check and make sure the Vbias resistors (R12 and R13) are correct... if R12 was 47R instead of 47k then it would cause voltages pretty much exactly as measured. There are a few other 47R resistors in the circuit, so it would be an easy mistake to make since all but one of the color bands are the same.

[antonis]

I would triple-check and make sure the Vbias resistors (R12 and R13) are correct...

In such a case, IC1_B should also be misbiased..

IC1
Pin 1: 8.20v
Pin 2: 3.12v
Pin 3: 2.47v
Pin 4: 0v
Pin 5: 4.31v
Pin 6: 4.32v
Pin 7: 4.28v
Pin 8: 8.61v

[ElectricDruid]

I would triple-check and make sure the Vbias resistors (R12 and R13) are correct...

In such a case, IC1_B should also be misbiased..

IC1
Pin 1: 8.20v
Pin 2: 3.12v
Pin 3: 2.47v
Pin 4: 0v
Pin 5: 4.31v
Pin 6: 4.32v
Pin 7: 4.28v
Pin 8: 8.61v

Yeah, good point Antonis.

How about a short on C1? Then the Vb would be split by a voltage divider made of R1 and Rpd1. Now 2Mohms isn't going to load the VB divider much, so you'd expect about 50% of the voltage. So if anything pin 3 looks a bit *high* for that theory (4.31V / 2 = 2.155V, not 2.47V).
Or perhaps a short on C4? That'd drag pin 2 down via R4.

Dunno. It's not obvious, to me at least. I'd definitely be looking for either a bad joint or a bit of solder/rubbish shorting something though.

[RickMcCarthy]

All good places to search and I sure appreciate this input. I'm going to dig in when I get home this afternoon. I'll report my findings and with a little luck, it'll be working.

[RickMcCarthy]

Ok, so I checked R12 and 13 - both are 47K and correct. I tested R12 and one lead is getting the full VA (8.61v) and the other side reads the same as the end of R13 that it's tied to (4.25v), but the strange thing is that I read 0v on the + pad of C10. As a contrast, on the "B" side of the pedal I read the 4.25v on the + pad of C20.

I even tried installing another 100uf/25v cap I have here and same thing - no 4.25v on the + pad. When I install a small jumper from the C12/13 junction to + of C10... still nothing.

This has got me stumped. Considering starting over, though I'd really like to see this through.

[RickMcCarthy]

IC 1 reads:

IC1
Pin 1: 8.12v
Pin 2: 2.40v
Pin 3: 2.30v
Pin 4: 0v
Pin 5: 1.99v
Pin 6: 2.00v
Pin 7: 1.96v
Pin 8: 8.61v

[Rob Strand]

IC 1 reads:

IC1
Pin 1: 8.12v
Pin 2: 2.40v
Pin 3: 2.30v
Pin 4: 0v
Pin 5: 1.99v
Pin 6: 2.00v
Pin 7: 1.96v
Pin 8: 8.61v

To me the part of the circuit around pin 5, 6, 7 seems to be working and that VB would appear to be at 2.0V.
The weird thing the pin 3 is greater than 2.0V.  When the DMM loads down pin 3 you would
expect the pin 3 voltage to be less than 2.0V.   Then there's the question what is making VB low.
Only the 1M (R1) around the circuit involving IC1 pin 1, 2,3 connects to VB and R1 cannot make VB pull
down to 2V.

So there's two problem:  why is VB 2V and how can pin 3 get greater than 2V.
One possibility is IC1 is fried.

Maybe check your soldering on IC1 and check for shorts on the board.

[RickMcCarthy]

Not a fried chip. Being a dual pedal I was able to swap the chips and both work in side "B" so I think that rules out a bad op amp.

[RickMcCarthy]

I would triple-check and make sure the Vbias resistors (R12 and R13) are correct... if R12 was 47R instead of 47k then it would cause voltages pretty much exactly as measured. There are a few other 47R resistors in the circuit, so it would be an easy mistake to make since all but one of the color bands are the same.

I did have the correct value on R12 & 13. What about no voltage in C10? There is a trace from the intersection of R12&13 to the + pad on C10, correct? The working "B" side has voltage on + pad of C20 and that's one of the more telling differences I can find. I even changed C10 to another cap but nothing. Am I after a red herring?

[FiveseveN]

There is a trace from the intersection of R12&13 to the + pad on C10, correct?

Yup. Is there continuity between all these pads and pin 5 of the op amp?

[Rob Strand]

Not a fried chip. Being a dual pedal I was able to swap the chips and both work in side "B" so I think that rules out a bad op amp.

OK cool.  You need to do some measurement at other points.

Ok, so I checked R12 and 13 - both are 47K and correct. I tested R12 and one lead is getting the full VA (8.61v) and the other side reads the same as the end of R13 that it's tied to (4.25v), but the strange thing is that I read 0v on the + pad of C10. As a contrast, on the "B" side of the pedal I read the 4.25v on the + pad of C20.

I was thinking some of your symptoms could be explained by C10 being reversed.  I searched for C10 in the previous posts and now I see the + pad of C10 reading 0V I'm getting more convinced.

[antonis]

I did a fresh set of readings just now and here's what I've got:

IC1

Pin 1: 8.20v
Pin 2: 3.12v
Pin 3: 2.47v
Pin 4: 0v
Pin 5: 4.31v
Pin 6: 4.32v
Pin 7: 4.28v
Pin 8: 8.61v

IC 1 reads:

IC1
Pin 1: 8.12v
Pin 2: 2.40v
Pin 3: 2.30v
Pin 4: 0v
Pin 5: 1.99v
Pin 6: 2.00v
Pin 7: 1.96v
Pin 8: 8.61v

Sorry but I'm confused now..
The more recent the measurements the worse the readings..??

[Rob Strand]

Sorry but I'm confused now..
The more recent the measurements the worse the readings..??

There's a few things that don't add up in the thread.   I'm just sticking to the low hanging fruit.

The first set of readings at least had pin 2 and pin 3 at a lower voltage than VB, due to DMM loading of the 1M resistor.

We don't know if the gain pot position changes the voltages.  The gain pot could be in different positions in different tests.

It's possible changing the 100uF changed the observed VB voltage.   And if the 100uF cap is reversed, it's also possible IC1A vs IC1B measurements were done at different times and the reverse cap leakage was changing with time.

Plenty of ways to speculate possibilities but it's easier just to check the 100uF polarity!