SOLVED UniCab not working

[Crowbar]

Hello all,

I just finished building a UniCab pedal, but it's not working. I get a high pitch noise and turning the knob changes the pitch of the noise. It sounds like when you are trying to tune an old AM radio

I'm a complete amateur at this, any suggestions where to start looking for the fault?

Thanks in advance

 

[Robert]

I assume there are plastic covers on the pots under the PCB?

Where'd you get your TL072's? Have you tried reseating them in the sockets?

Does it pass signal in bypass?

Make sure neither of these lugs are touching the enclosure or DC jack nut.

 

[Nostradoomus]

looks like your red wire at the DC jack might be on the switched (battery +) terminal. You'll want it on the 9v lug. Could be wrong, hard to see.

 

[Crowbar]

I assume there are plastic covers on the pots under the PCB?

Where'd you get your TL072's? Have you tried reseating them in the sockets?

Does it pass signal in bypass?

Make sure neither of these lugs are touching the enclosure or DC jack nut.
View attachment 93040

Yes, all pots have the plastic covers.

I bought it as a kit from Musikding. I will try re seating the IC:s. Im not sure I'm doing it right, the legs are always wider apart than the rows in the sockets so I bent them inwards with a plier before inserting in the sockets. Is there a more correct way to do this?

Bypass signal is fine. I will re arrange the jacks a bit, I agree the lugs are too close to other parts

Thanks a lot

 

[Robert]

I insert one side of pins into the socket then apply some pressure from the side to align the other side, then push down....

I think the more widely accepted approach is to press down against a flat surface (or use a lead forming tool).

 

[Crowbar]

looks like your red wire at the DC jack might be on the switched (battery +) terminal. You'll want it on the 9v lug. Could be wrong, hard to see.

View attachment 93041

I haven't quite figured out which one is which of the + lugs, so I always connect the red wire to both.

It has worked in all my other pedal builds, and the led on this one lights up when it should, so I don't think this is an issue. But I might be wrong of course, wouldn't be the first time

Thanks for your input anyway, I appreciate it

 

[Crowbar]

A small update, I measured the voltage on al IC pins and noticed that pin 4 on IC1 had +5 v, which seemed wrong since that's the ground pin. I removed the IC and put it back again and now pin 4 is at zero v. I think I had managed to bend pin 4 so it touched the neighbour pin somehow.

Unfortunately the pedal is still not working, it only delivers some crackly noise when engaged. And now the led is lighting even when the foot switch is off, but fainter. And it flickers if I move the PCB around so I think there is some grounding issue in one of the cable connections. I will redo the wiring for the DC and audio jacks, the cables were a bit too short anyway

 

[Nostradoomus]

can we see a picture of the solder side?

 

[Crowbar]

This took a very strange turn. I re did all the cables, adding some length for a bit neater routing.

Still not working, AM radio in full swing and flickering led in bypass mode.

Then I played a bit with the UniCab turned off, and then turned it on again, and suddenly it's working. No led flicker and it sounds great. All knobs working and doing what they are supposed to do.

I have no idea what has happened.

 

[Nostradoomus]

loose connection somewhere

 

[Crowbar]

I think I need to practice soldering more. I use too much solder sometimes I think, I get these "balls" of solder on the components side, like on the resistors in the photo.

And sometimes there is no solder at all in the holes.

I don't know if this inconsistency is the reason for my troubles?

 

[Crowbar]

I don't know if anyone is reading this, but anyway, I have decided to give up on this pedal for now, I don't know how to fix it.

One minute it works fine and then out of the blue it starts crackling, or whining or go completely silent. And operating the top left pot you can get all of the above depending on the position of the pot.

Maybe the pot is broken, I have ordered a new one, will replace it and try again but I don't have high hopes, most likely this cracle-beep-fest will continue.

It's a shame because the short moments it works it sounds really good but it seems a too difficult project for me.

I have built several other pedals without any issues but this seems impossible.

Rant over, thanks for all helpful replys.

 

[Lytt Effects]

Now you listen, ain’t no giving up here. We’ve all been there, so let’s get this thing working and get your confidence back up. You got this.

More pictures would be helpful. Looking at those solder joints, they seem a bit cold, so it could be as simple as a cold/broken joint somewhere that haphazardly makes connection. Are you soldering your resistors on the top of the board (component side) like that, or from the bottom? If that’s from the bottom, that is way too much solder. Regardless, balling up like that means the heat transfer isn’t taking, which is usually a sign of not enough heat, or poor timing, or both.

When troubleshooting, it’s best to follow these steps:

1) make sure all component values are correct and verified

2) make sure all polarized and direction-specific components are properly oriented: electrolytic caps, ICs, diodes, etc.

3) beware of accidental grounds/shorts when the board is housed. Most common culprit is a long lead being bent and touching something, or a metal LED bezel contacting something

4) all joints are reflowed, and board is checked for accidental solder bridges in tight spaces

5) bottom of board is cleaned - I use isopropyl alcohol and a brush and then a microfiber towel to dry it up

6) begin audio-probing along the circuit path to pinpoint the issue

Again, more pictures and clear pictures will help us help you, especially on the underside of the board. We need to see the whole picture.

 

[Crowbar]

Now you listen, ain’t no giving up here. We’ve all been there, so let’s get this thing working and get your confidence back up. You got this.

More pictures would be helpful. Looking at those solder joints, they seem a bit cold, so it could be as simple as a cold/broken joint somewhere that haphazardly makes connection. Are you soldering your resistors on the top of the board (component side) like that, or from the bottom? If that’s from the bottom, that is way too much solder. Regardless, balling up like that means the heat transfer isn’t taking, which is usually a sign of not enough heat, or poor timing, or both.

When troubleshooting, it’s best to follow these steps:

1) make sure all component values are correct and verified

2) make sure all polarized and direction-specific components are properly oriented: electrolytic caps, ICs, diodes, etc.

3) beware of accidental grounds/shorts when the board is housed. Most common culprit is a long lead being bent and touching something, or a metal LED bezel contacting something

4) all joints are reflowed, and board is checked for accidental solder bridges in tight spaces

5) bottom of board is cleaned - I use isopropyl alcohol and a brush and then a microfiber towel to dry it up

6) begin audio-probing along the circuit path to pinpoint the issue

Again, more pictures and clear pictures will help us help you, especially on the underside of the board. We need to see the whole picture.

Thanks for the encouragement, I will not give up of course but when I posted I was really tired of this thing..

It's like every time I try, it malfunctions in a different way, sometimes dead silent, sometimes loud crackling and once in a while the sound that killed the aliens in "Mars attacks"

And a few times it actually worked and sounded great, so I don't think I have the components in the wrong positions or orientations. But after a while spontaneously going back to crackle, without me touching anything

I think you are right that this is caused by some loose connection somewhere, my solders don't look good, I have a hard time getting the solder to flow out on the pad, it wants to stick to the component legs as balls. I have a cheap Velleman soldering station, with a temperature knob, but I'm pretty sure it's not really temperature controlled, its just a resistor so the numbers on the dial are probably not real. I have it at 400 degrees, but maybe that is not enough?

I added a few photos, unfortunately the pots cover half the PCB and I have already bent them up once to check for faults and Im afraid if I bend them up again the legs will break off.

From the photos you can see my failed soldering, the solder looks like onions on the component legs

Thanks a lot for the help, I really need it

 

[Lytt Effects]

Thanks for the encouragement, I will not give up of course but when I posted I was really tired of this thing..

It's like every time I try, it malfunctions in a different way, sometimes dead silent, sometimes loud crackling and once in a while the sound that killed the aliens in "Mars attacks"

And a few times it actually worked and sounded great, so I don't think I have the components in the wrong positions or orientations. But after a while spontaneously going back to crackle, without me touching anything

I think you are right that this is caused by some loose connection somewhere, my solders don't look good, I have a hard time getting the solder to flow out on the pad, it wants to stick to the component legs as balls. I have a cheap Velleman soldering station, with a temperature knob, but I'm pretty sure it's not really temperature controlled, its just a resistor so the numbers on the dial are probably not real. I have it at 400 degrees, but maybe that is not enough?

I added a few photos, unfortunately the pots cover half the PCB and I have already bent them up once to check for faults and Im afraid if I bend them up again the legs will break off.

From the photos you can see my failed soldering, the solder looks like onions on the component legs

Thanks a lot for the help, I really need it

When you say 400°, do you mean Fahrenheit, or Celsius? I hope Celsius, but given the heat transfer issues, it’s either F, or a very dirty tip. In order to transfer to both the lead and the pad, you’ll need a lot of heat (I’m at 340° C - 644° F), a clean tip (make sure you’re wiping it on either a slightly damp sponge or steel wool every few joints), and the right style/size (I use a chisel type that’s on the smaller side) to make good contact with both. More importantly, timing. Here’s my process:

- clean tip
- wet tip with solder
- wipe on steel wool to leave a small layer on tip
- press to pad/lead, hold for 2 seconds
- apply solder - this is the tricky part. Ideally, you want to be able to apply to just the lead/pad and not hit the tip. If it’s not taking, you can try creating a wet solder bridge by just barely hitting the tip with the solder to get it flowing. You don’t need a lot.
- once solder has been applied, pull strand away, hold tip for two seconds, remove, let dry. Do not blow on it. Work patiently.

 

[Lytt Effects]

 

[Lytt Effects]

Also, your solder selection is very important. What are you using?

 

[Crowbar]

When you say 400°, do you mean Fahrenheit, or Celsius? I hope Celsius, but given the heat transfer issues, it’s either F, or a very dirty tip. In order to transfer to both the lead and the pad, you’ll need a lot of heat (I’m at 340° C - 644° F), a clean tip (make sure you’re wiping it on either a slightly damp sponge or steel wool every few joints), and the right style/size (I use a chisel type that’s on the smaller side) to make good contact with both. More importantly, timing. Here’s my process:

- clean tip
- wet tip with solder
- wipe on steel wool to leave a small layer on tip
- press to pad/lead, hold for 2 seconds
- apply solder - this is the tricky part. Ideally, you want to be able to apply to just the lead/pad and not hit the tip. If it’s not taking, you can try creating a wet solder bridge by just barely hitting the tip with the solder to get it flowing. You don’t need a lot.
- once solder has been applied, pull strand away, hold tip for two seconds, remove, let dry. Do not blow on it. Work patiently.

It's 400 degrees Celsius, but I don't know how accurate it is.

My process is similar to yours but I think I am trying to do it quicker, maybe too quick. Im afraid I will destroy the components if I heat them too long.

I do try to direct the solder to touch the pad instead of the leg, but it's tricky, some pads are very small. The pots and foot switch are much easier to do

The solder is 60/40 tin/lead, brand is "Tubman"

Thanks a lot for the instructions

 

[Caedarn]

I’m not very experienced with troubleshooting so take this FWIW…

Have you tried testing the PCB outside of the enclosure? I’ve had a few cases where a PCB worked prior to boxing, but had weird issues after. You might get some clues at least if it exhibits different behavior outside the box.

It’s curious to me that you see a lot of issues when turning one of the pots. It looks like you’ve got covers which is good but is there any chance contact is getting made somehow to the legs or case?

I was having trouble with a project one time and got weird behavior when turning a pot and finally figure out the pot was the issue. I think maybe I damaged it when bolting it into the enclosure.

Also, sometimes it’s good to take a break and come back to it later.

 

[Erik S]

Are you sure none of your IC legs are folded under now? That could give you intermittent contact.