Green Bean problems, fried resistor

[Tuxedo3]

Hey guys, I recently built the Green Bean (cool circuit btw) and I went to test it the first time and realized that 1. there was no output no matter what I did and 2. something was getting pretty warm by the bottom portion right of the circuit. I just tested it again today with my meter and was reading 0v at the IC, but then I suddenly realized that R18, which is 47 ohms, was all brown and SUPER hot. (third component from the bottom)




I like to think I'm OCD about my solder joints but I definitely could've made a mistake. Looking at the schematic, http://www.madbeanpedals.com/projects/GreenBean/docs/GreenBean2015.pdf, it looks like my issue could lie in one of a few things.

1. Bad R18
2. Bad C11 (putting 9v to ground?)
3. Bad Q2

Has anyone experienced anything like this or do they see what I did wrong? I tried to include pictures to help identify the issue. I can post any other pictures as needed. Thanks in advance.

[Tdub]

Sounds like dumbness but considering that R18 is pretty much right at the input of the dc power, I'd be first looking at the power you're using.

Is it 9v DC? Check it's not AC or way higher than 9v.
Is there any way you can check it using a battery?

Have you tried changing out those parts you mentioned?
I think if c11 was going straight to ground it wouldn't necessarily get the resistor burning out.

[Tuxedo3]

Is it 9v DC? Check it's not AC or way higher than 9v.

I was using my Pedal Power, so I assumed it was 9V dc the first go around, this last time (when I noticed it all burnt) I did check it with a meter and it said 9.3V DC.
I could definitely try it using a battery, good idea.

Have you tried changing out those parts you mentioned?

That's kind of the next step, I'm going to take that resistor out and see if it's good.

[somnif]

If R18 is cooking I'd imagine the most likely cause would be a short to ground across it. Any solder bridging hiding near by?

[Tuxedo3]

I checked all around it and can't seem to see a short to ground anywhere. Honestly I'm really confused about it because all the connections look fine. The resistor still shows 47 ohms on my meter. Should I replace it anyways?

[jimilee]

I checked all around it and can't seem to see a short to ground anywhere. Honestly I'm really confused about it because all the connections look fine. The resistor still shows 47 ohms on my meter. Should I replace it anyways?

Did you check continuity to ground where shouldn't be?


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[somnif]

That was going to be my suggestion, red probe on 9v+ and start poking on the right side of R18 and go from there. If you're not getting output with the pedal engaged then it's likely most of the circuit is not getting juice.

Does the signal make it through the pedal in bypass mode?

Does the LED light when the pedal is on?

[Tuxedo3]

Replaced R18 and C11. Within 10 seconds of giving the circuit power, R18 begins to smoke and turn dark brown.

Did you check continuity to ground where shouldn't be?

I tried, but I don't feel comfortable enough with that to draw conclusions that could benefit me. It seemed like the positive side of C11 was connected to ground, which is why I replaced it but the new one seems to also be.

That was going to be my suggestion, red probe on 9v+ and start poking on the right side of R18 and go from there. If you're not getting output with the pedal engaged then it's likely most of the circuit is not getting juice.

I get 9v on the right side of R18 as its cooking but nothing on the left side.

Does the signal make it through the pedal in bypass mode?

Does the LED light when the pedal is on?

I am currently just testing to make sure the circuit would even read the correct voltages (which it never did) before I connect it to a 3pdt. And I do not have an LED connected currently, i could add one though.

[somnif]

Ah, I saw something soldered in the LED holes and assumed. My mistake. Very odd.

Silly question, but is your 9v plug socket wired correctly?

[Tuxedo3]

Ah, I saw something soldered in the LED holes and assumed. My mistake. Very odd.

Silly question, but is your 9v plug socket wired correctly?

Just double checked this because you asked, yes it is. Does something need to be soldered to the "G" pad at the bottom?

[midwayfair]

Remove all the active components (the two transistors and the chip).

Measure DC at:

Both sides of R18
Both sides of R19;
All holes where the active components would normally go. Look up the datasheets for the components if you aren't sure of the pin numbers or names.

Write them down and post them.

If you have 9V on both sides of R18 during this test, do this:

Put the active components back in one at a time and repeat. Then put both transistors in and repeat. Then put the chip in and repeat.

If you do not have 9V on the other side of R18 during this test, your paths to ground are:
C11 being bad (shorted) or backwards (more likely)
Continuity to ground because of a short at pin 8 of the op amp, the collectors of the transistors, C11, or (very unlikely) C12.

If you don't know how to take voltages, there are instructions online and in the tech help rules thread.

[Tuxedo3]

Triple checked power supply - 9.13v
Left side of R18 - 8.9v
Right side of R18 - 0v
All holes where active components would go - 0v

C11 is in the correct way as the PCB has labelled.
Does this mean there is definitely a short somewhere?

[midwayfair]

Triple checked power supply - 9.13v
Left side of R18 - 8.9v
Right side of R18 - 0v
All holes where active components would go - 0v

C11 is in the correct way as the PCB has labelled.
Does this mean there is definitely a short somewhere?

Set your meter to continuity to find out. You can't necessarily see a short with your eyes.

Reflow all your solder joints as well.

[wgc]

Double check the orientation of your ic.

Dual op amps and components in line can get pretty hot if the ic is in backwards.

You can't always go by the circle if it has a flat bottom, sometimes (not often) it's just an ejection point when they mold it. (If the bottom is scooped, like a semi sphere, it is an indicator.) Check the sides to see if one is beveled along the top edge. When in doubt check the manufacturer's data sheet. Jon gave pretty good advice.

Probably worth swapping the ic either way. Also check for shorts under the socket and bottom of pcb.

Good luck!

[Tdub]

Pictures of the other side of the board could help too