SOLVED Blue Breaker no bias voltage

[clarksjc]

Hello, I am new here. I have built a few pedals point to point but not with a pcb. I will consider myself a newbie at this point since I can't seem to get this working. I have replaced some of the off board wiring that has since broken from moving it too much
I found that my voltage at the op amp is about 9v at pin 8, 0 at pin 4, about 2.5v at pin 2. All other pins are 7.49 to 8v. I will get the exact voltage tomorrow if needed.

I get about 9v at the junction of R11 and R12. 9v both sides of D5. So no bias voltage after the voltage divider if I am saying that correctly. Nowhere on the board.
I have since replaced C9 since it had a bad connection and I thought maybe I damaged it. Voltage also almost 9v at the positive side.

Anyway, the bypass works, the led comes on, but no sound. I used an audio probe and had a signal until C1 but nothing after. I also reflowed joints and cleaned the board.
I am fairly certain its my own doing, but need some help to figure it out please. I just want to get it working and then clean up some of the wiring. Thanks for any suggestions.

Sean

 

[clarksjc]

Continuity checked out good. Here are the voltages for the TL072:

Pin 1: 8.59 volts
Pin 2: 8.54 volts
Pin 3: 6.89 volts
Pin 4: 0
Pin 5: 7.58 volts
Pin 6: 7.57 volts
Pin 7: 7.34 volts
Pin 8: 9.10 volts

Pin 3 is higher since my first post interestingly.

 

[music6000]

Pins 1, 2, 5 are VREF & should be 4.5v, so something is wrong in this area around R11 & R12 47k.
Is R12 going to ground :

 

[clarksjc]

I agree, Robert said that early on and you've been pointing there too. Pin 3 seemed to change right after I replaced R11, not a bad resistor but something must be wrong in that area (caused by me).

Could be a short even though reading continuity? I'll poke around a bit more, then I may just build another board. The rest works great.

I learned a boat load from this, and really appreciate the help!

 

[music6000]

I agree, Robert said that early on and you've been pointing there too. Pin 3 seemed to change right after I replaced R11, not a bad resistor but something must be wrong in that area (caused by me).

Could be a short even though reading continuity? I'll poke around a bit more, then I may just build another board. The rest works great.

I learned a boat load from this, and really appreciate the help!

When Testing Continuity for Yellow & Red, put Yellow to Green & Red to Green to see if there is continuity, there shouldn't be!

 

[clarksjc]

I will try this tomorrow, thanks. To answer your question from earlier that I overlooked, yes R12 is going to ground.

 

[clarksjc]

All checks out good, in other words no continuity between different colors.

Question, could this IC internally cause this hard to find "short" or whatever if it were malfunctioning? I ordered
more sockets and IC's so I can do it right.

As I mentioned, I soldered it in .

 

[music6000]

Yours looks like a Genuine TL072 BUT if too much heat is absorbed, it could screw it up internally.
I only used Machined Sockets on all my OpAmps.
Personally, I would cut each leg off at the top of the IC so you have 8 pieces you can grab with Tweezers & desolder one at a time.
Once removed, you can heat each pad individually and with a straw or plastic tube & you blow really quick at the same time as you take the soldering iron away with a Pffffff and you end up with a clean hole.

 

[clarksjc]

Awesome thanks! Been struggling whenever I replace anything. Sounds like a great method.

 

[clarksjc]

I want to thank everyone too and music6000 for your expertise and help. My lack of experience building pedals has just been stepped up a notch by learning from dumb mistakes of my own.
Feel free to let me have it, I deserve it!

It was the IC, or a short I caused when I soldered it. I don't know.

But here are the voltages now, with it pressed in to test.

Pin 1: 8.44
Pin 2: 4.48
Pin 3: 4.04
Pin 4: 0
Pin 5: 4.48
Pin 6: 4.49
Pin 7: 1.46 (Not sure about this one since it is not soldered in and might have moved around)
Pin 8: 8.98

I did a quick check that the pedal is working and it is. I might still build another!

 

[music6000]

I want to thank everyone too and music6000 for your expertise and help. My lack of experience building pedals has just been stepped up a notch by learning from dumb mistakes of my own.
Feel free to let me have it, I deserve it!

It was the IC, or a short I caused when I soldered it. I don't know.

But here are the voltages now, with it pressed in to test.

Pin 1: 8.44
Pin 2: 4.48
Pin 3: 4.04
Pin 4: 0
Pin 5: 4.48
Pin 6: 4.49
Pin 7: 1.46 (Not sure about this one since it is not soldered in and might have moved around)
Pin 8: 8.98

I did a quick check that the pedal is working and it is. I might still build another!

You did well, others would have thrown in the towel & put it in the Box of Shame!

 

[clarksjc]

that's hilarious! Thanks again!