smoothie

[1878]

Hello Everyone...

I recently finished a Smoothie build, but I've run into a problem... Basically, no phase !! I've slowly turned the 250k trimmer a few times trying to dial it in, but very little if anything at all happens. 

I get a small/quiet/weak amount of phase if I remove one of the transistors & the speed knob works as it should when I do this.

I've used all the correct value components other than the transistors, where I used matched 2n5952's. I flipped these 180 degrees to match the pinout of the listed 2n5457's.

I've also taken some readings...

9.29v going in

IC1

1. 3.67
2. 3.67
3. 2.48
4. 0.01
5. 3.67
6. 3.67
7. 3.67
8. 3.67

IC2

1. 3.67
2. 3.67
3. 3.67
4. 0.01
5. 4.38
6. 4.80
7. 4.80
8. 9.06

Q1

G. 3.16
S. 3.67
D. 3.67

Q2

D. 3.67
S. 3.67
G. 3.16

It seems that 3.67v is a very common reading !!

Any help would be greatly appreciated. Thanks.

[Kevin Mitchell]

Shouldn't pin 8 of the 1st opamp be equal to the V+ voltage (9.29)? Then again I have no idea what ICs are being used. The .13V difference on IC2pin8 and your V+ voltage seems to be off. Try to get a more accurate reading if possible.

You should also share the schematic for the project. That is a must. But you have my guess of where to check out.

[1878]

Not a problem. Here is a link to the build PDF which includes a schematic...

http://www.madbeanpedals.com/projects/Smoothie/Smoothie_2015.pdf

Thanks.

[Govmnt_Lacky]

Shorted trace between Pins 7 and 8 of IC1 

Pin 8 of IC1 should be the same as Pin 8 of IC2

[Kevin Mitchell]

It seems that 3.67v is a very common reading !!

Perhaps it is in these connections that hold a clue to where the problem could lie (an obvious short)

I'm definitely not as intuitive or knowledgeable as most of the members here but my suspisions would be a short. Perhaps more than one.

[Govmnt_Lacky]

The .13V difference on IC2pin8 and your V+ voltage seems to be off.

This is due to the diode drop. Normal

[Kevin Mitchell]

This is due to the diode drop. Normal

Darn voltage protection diodes!
Still learning - always learning
Thanks!

[1878]

Thanks for the replies.

By shorted trace, do you mean 7&8 are connected ??

[Kevin Mitchell]

Thanks for the replies.

By shirted trace, do you mean 7&8 are connected ??

Yes it is very obvious by your reading if they are indeed accurate.

You can see pin 4 gets ground and pin 8 should be getting +9v (v+). Something is definitely wrong there.

[Govmnt_Lacky]

Thanks for the replies.

By shirted trace, do you mean 7&8 are connected ??

Yep!

That is the first place to look. Also check IC orientation.

If there is no short, follow the V+ supply line back from IC1 Pin 8. Since IC2 has the proper V+ on pin 8 then you know it is good from there to the V+ input to the PCB.

[1878]

Thanks again.

I've just reflowed all solder joints around both IC's. I'm getting slightly different readings, but I can't make too much noise at the moment due to a sleeping 3 y.o.

I'll get the audio probe onto it tomorrow.

[Govmnt_Lacky]

Thanks again.

I've just reflowed all solder joints around both IC's. I'm getting slightly different readings, but I can't make too much noise at the moment due to a sleeping 3 y.o.

I'll get the audio probe onto it tomorrow.

And the voltage at IC1 Pin 8? 

[Tony Forestiere]

Also confirm that pin 4 of both chips is directly connected to ground. Just because they read 0v doesn't necessarily mean they are grounded.

[1878]

Just had 10 minutes to have another look...

IC1 has the same readings as previous other than pin 8 which is now 9.06v. Both pin 4's go to ground.

IC1 is a TL072CP
IC2 is a TL072IP

I've tried the trimpot again to no avail. I still get the booey phase effect when I remove either of the transistors.

Thanks.

[Kevin Mitchell]

I'd keep checking for shorts seeing how you have very similar readings all over.

Sorry I'm not savvy enough to point them out. If you go off the schematic and notice the same readings on pins that are next to each other but should not be connected, those are points of suspicion. Maybe you skipped a lead while soldering, maybe it looks good but isn't. Check that all components are soldered and mounted well.

You could use an audio probe and follow as you get close to the final sound it's producing. Along the way you will find your suspects.

These two methods will keep you busy. The problem usually is a quick fix that you tend to miss. Keep at it.

[1878]

Yuppity. I have a feeling it's something VERY simple. I didn't realise you had to use the smaller resistors, but I did take extra care to ensure there wasn't anything touching something it shouldn't.

I'm in work for 5 a.m tomorrow so it's an early night for me, but I'll get the audio probe onto it this weekend.

Thanks again.

[Govmnt_Lacky]

If you get a chance, please repost voltages for ICs and transistors. Would like to see what the changes are now that IC1 Pin 8 is at 9V.

EDIT: Also, verify that D2 is a 4.7V Zener. You should have 4.7V on the banded side. If not, then that could be your problem.

[1878]

Readings for IC1 are exactly the same as before other than pin 8. Diode is a 4.7v too. I get a 4.7v reading.

[1878]

I beg your pardon. I'm getting 3.67v !!

[Govmnt_Lacky]

I beg your pardon. I'm getting 3.67v !!

I was gonna catch that...

The voltage on the Zener should match the voltage on the Drain of Q2 and Q1(2N5952)

If you cannot verify the part number on that Zener, I would replace it if I were you. Maybe even try a 5.1V. Something that puts 4.7V on the banded side.