Troubleshooting 101?

[CasterPaul]

So,
I am wondering if there is a common process in troubleshooting circuits that SHOULD work but for some reason don't. The particular schematic I'm building is here: www.freeinfosociety.com/electronics/schemview.php?id=1136]
All voltages test right whether 9v or half. Polarities are right, grounds constant. I have the tip of my input jack plugged to the input(right in between the cap and 1M res. The ring and sleeve go to ground (when closed) . Output jack tip connected to out (between pos lead of cap and resistor going to ground) and sleeve to ground. All of the places on the schematic that show arrows to the pots  are connected to the middle of the pots... plug it in and no sound... Help please!! Oh yah, it's on a breadboard

[Govmnt_Lacky]

I would recommend trying this...

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[jrod]

And, If that does not work, just copy this exactly: http://www.beavisaudio.com/bboard/projects/bbp_BoutiqueTubeScreamer_Rev1_1.pdf

[jkokura]

I think he's wanting a step past that. I think he wants to learn more about how to fix things himself. That's a good start, but usually is useful in getting others to help from here.

Because you're working on a breadboard, my first impulse is to say you did it wrong somehow. If you haven't got the circuit working, then start over. With a bread board that should be easy. If it's too complicated to start over, I say start over with something easier. Learn to use the bread board and then try again.

My trouble shooting usually begins with examining the parts and wiring, triple checking everything for proper orientation, value, and placement. Once I'm sure, I then start using an Audio Probe to follow from the input into the circuit, and out the other end. If it's not working, usually I can find the problem that way.

Jacob

[R.G.]

I am wondering if there is a common process in troubleshooting circuits that SHOULD work but for some reason don't.

The stuff I wrote up for "what to do when it doesn't work" catches the majority of issues, but not all. Most flaws are reflected as DC-only issues or AC plus DC issues, which that procedure catches.

What it does not catch is purely AC problems. It will not catch an open capacitor between sections or a bad PCB trace or bum breadboard contact that is in an AC-only part of the circuit. There are many fewer of these but they do exist.

When that happens, you do signal tracing. The oscilloscope is the way it ought to be done, but the audio probe is what people without oscilloscopes do it. Follow the signal from input through the circuits. When the signal vanishes, back up a step.

[CasterPaul]

The audio probe was really helpful. I traced down the line and had some unnecessary shorts and found out I jumped the wrong components to terminals 1 and 2 of the IC! thanks for your help. It works fine now, but it seeme like it's lacking volume and there is no high end (my tele all the way open on the bridge sounds like a rolled off neck pickup!). Also, when I turn the tone pot (that's the one with the cap to resistor to ground right?) past about 10%, the volume goes to  a really low level... I thought maybe I'd switch the two outside lugs, but it didn't help anything. Any ideas?

[jkokura]

Sounds to me like either you've got the pot wired wrong, or your tonestack has a problem somewhere. Is it possible for you to take some readings and post the Voltages as the debugging thread describes?

Also, good pictures of the board and pots will help us see if there's something we can spot. I have built multiple tubescreamers, and it shouldn't sound as you're describing.

Jacob

[CasterPaul]

q1         q2      IC1
c:9.4     c:9.4   1:4.7        5:4.7
b:1.4     b:1.5  2:4.8        6: 4.7
e:.83     e:.85  3:4.6        7: 4.7
                      4:0(gnd)   8: 9.4

D1           D2         D5         
A:4.7       A:4.7     A:0 (gnd)
K:4.7       K:4.8     K:9.5

I did everything as said on the schematic, skipped the LED, then added it, took it back out again for simplicity. How can I post pics of the pots?

[CasterPaul]

also, the last cap the 10uf only measures .9v is that normal? used a fresh 9V

[jkokura]

I don't necessarily see anything wrong with your numbers. They look fine. As for the output cap, I have no idea what that reading means.

Do you still have the same issues? Have you tried the pedal with another pedal with a built in buffer (eg. Boss)? Have you tried going through the tonestack section with your audio probe to see where the crazy blanket starts?

Jacob

[CasterPaul]

I'll try it thru another pedal. I'm a little unfamiliar with the tonestack and how pots work. arent they just a resistor with a wiper in between it?

[PRR]

> had some unnecessary shorts and found out I jumped the wrong components to terminals 1 and 2

General Rule: if you have one mistake, you probably have another.

Repeat.

There's a LOT of pins here.

And a hole-array breadboard is NO help getting organized.

Go fishing. Paint the porch. Read Forth Mansions.

Come back through with FRESH eyes. Forget how you "know" you wired it. Look at what is really there.

Ideally you'd have an innocent friend review it. I've had impossible won't-work problems, some student looks and asks "is that supposed to be here?" But teaching normal people how a hole-array circuit works at all is improbable. (With PCB layouts and pretty pictures, an innocent can check.)

Oh.... and your base voltages are both wrong. I'd expect 3V-4V, not under 2V. C and E reversed? 1K where should be 10K?

[CasterPaul]

I think he transistors are right... C B E left to right with flat side facing you and top mid to bottom on the schematic right? How'd you come up with the voltages for the bases and other parts?