Non-Bean Tourbillon Help

[Droogie]

I built a Tourbillon but am not getting LFO. LED responds to Shape control; Depth control also works.
Rate control doesn't have effect and LED stays lit at whatever intensity is determined by Shape.

I checked component values and they match specs
Reflowed solder around the IC and resistors 15, 16, 17, 18, 19, 20 and 21 and caps 10, 11, 13 and 15
Checked for solder bridges
Tried a known working 072

Is there any other spot I should be looking at?

Thanks!

[RobA]

Check voltages around the TL072. What voltage do you see at pin 5? Is it moving there? Are the supply voltage right on the IC?

[Droogie]

Thanks. I'll take a look this evening.

[Droogie]

The voltages look like this:

Pins 1-3 and 5-7 are all @ 4.67;
pin 8 is @8.4;
pin 4 is 0.
There is no movement on pin 5.

Hmmm...

[RobA]

Those look like reasonable starting points to me. The first thing I'd check is around C14. Check it's value, orientation and it's continuity to the pads. If you have a continuity setting on your DMM, it can be really helpful for finding hard to see bridges and components that aren't making contact.

[GrindCustoms]

Juansolo and marauder did some leg work on this circuit to get it working like it should....

K Tourbillon sorted.

R13 & R14 are correct on the schematic, but not on the BOM (they're backwards on the BOM).
R11 wants to be 100k
R12 wants to be a 390k

All unity goodness now and it sounds rather brilliant with Tayda LDR and a 3mm clear orange LED. Gets a filtery/phasery/tremoloy thing going on. Do like.

You can find more info here, http://www.grindcustomsfx.com/forum/viewtopic.php?f=9&t=442

Those look like reasonable starting points to me. The first thing I'd check is around C14. Check it's value, orientation and it's continuity to the pads. If you have a continuity setting on your DMM, it can be really helpful for finding hard to see bridges and components that aren't making contact.

Good point, C14 is the timing cap.

[Droogie]

I'll check this out and report back. Thanks for the help!

[Droogie]

I swapped out the resistors as indicated in the referenced thread and checked continuity of C14, which was fine. Still no movement on pin 5. Any ideas for the next steps? Thanks again!

[RobA]

Can you put up a couple of photos, front and back?

One thing I noticed is that if you get very far off of the center of the shape control, the LFO movement is hard to see on the LED. Try to put the shape dead center when you watch it. This depended on the type of LED I put in it too.

[jimilee]

Also are you testing it on a test rig? If so you gotta cover it with something, and he's right you're good between 11 and 1 o'clock, after that not so much.

[Droogie]

In checking the board traces, I see that there should be continuity btwn the + side of C14 and R18 and then R18 and pin 5 of the 072.

I tried reflowing all joints involved and put Shape in the center, but no luck. Then I put  a jumper btwn C14+ and R18 and bingo, LFO!

I suppose I could solder in a  jumper and call it good. Is there a smarter way to do this? I reflowed several times and each component has continuity to the respective pad. If a jumper is the worst case scenario, that's fine.

[RobA]

Good detective work!

It's possible that the trace from C14 to R18 is damaged. If you look at the PCB with a magnifier of some sort, you might be able to see it. Could be the pad at C14 too. It seems like the joint at R18 is good because the connection to the IC is good there. If you need to make the connection with a jumper, that's really OK. There are plenty of production level shipping products out there with jumpers on their PCB's to correct flaws or design errors. It won't hurt anything to make the connection with a jumper here. The only thing I'd check for is that there isn't any continuity to ground at C14+ or the connection at R18. Although, it sounds like there shouldn't be because the LFO is working with the jumper in place.

[Droogie]

Thanks! And thanks for pointing me in the right direction. As always, the builds that don't fire up the first time are the ones that lead to learning more about the way circuits work (at least for less-knowledgeable folks like me  ). I look forward to playing with this one!