Supreaux Deux Faux Pas

[dropanchor812]

Alright, so I'm posting this over here because I am a beginner and the solution is likely something very simple that I'm just not considering. I went through every pedal troubleshooting article I that my attention span would endure, and now I am going public. 

First, I need to confess that I committed the cardinal sin of pedal building:  I did not rock it before i boxed it.  I hope all of you will be able to forgive my transgression and hear my plea of help despite my direct disobedience to this law, which is only meant to enhance our pleasure and not diminish it.  I did, however, try to rock it before I boxed it.  I made a pcb testing rig with the audio probe per jkotura's little tutorial and it worked great.  According to the probe, my problem lies at R1.  When I touch the probe to the left of R1 I get the signal, but when I touch the right end pad it is silent.  There looked like there was a hairline solder bridge between R1 and R2 on the left pad so I scratched around between them to break it.  It didn't really make a difference.  After that I thought it was a power issue and that my jack was wired wrong on the tester (and it was), so I just went ahead and boxed it thinking that once I got it in there it would magically work.

So its all wired up now in the box.  There is a loud hum and a very faint guitar signal coming out  (and I mean verrrrrry faint).  It bypasses fine and there is at least a very faint guitar signal coming through which tells me it is wired okay.  All of the pots work because the hum changes in volume or character when I use them and the fat switch.  The transistors have been biased at 12v.  When I measure R1 with my DMM I am getting a "0" reading.  R5 also uses a 1M resistor and it measures as it should, I also double-checked that it is the right value by the colored bands.  R2 also measures fine.  So I'm really feeling like R1 is the problem here.  The joints feels sturdy on both sides of R1.  If I would have done this the right way then I could show you a picture of the back of the pcb, but I'm confident its okay because I was checking all over for problems when it wasn't working in my testing rig.

I also figured out I could still probe the circuit by attaching an alligator clip to the tip of the output connected to a probe.  I was pretty proud of that little discovery (even though the circuit still isn't working), and confirmed that the problem is still at R1.

I'm kinda worried that I cut the trace when I was scratching between R1 and R2.  But that doesn't make sense because it would have completely eliminated the guitar signal, right?  I have tried figuring this out by looking at the schematic, but I'm still learning how to read them.  I just can't get over that there is a signal coming through, which increases and decreases in volume with the gain and volume pots.  The hum is much much louder, but that guitar signal is getting through somehow.  Any help is appreciated, thanks!

[hoodoo]

Hey mate, you might want to check C8, that should be a 68nf cap, Matt.

[midwayfair]

http://www.madbeanpedals.com/forum/index.php?topic=902.0
Did you read through Jacob's troubleshooting tips? He includes a lot of information that you need to post so that people can help make a diagnosis without the circuit in hand.

1. Post voltages taken on all transistors and at the output of the 18v charge pump.

2. Your picture only shows the top side of the circuit board. We need to see both sides (see #4), and your switch etc.

3. Link to the layout, schematic, and parts list you're using so we have a reference. Telling us the part number doesn't do any good if we don't know what it's suppose to be doing!

4. Your build worked when it was out of the box, then it didn't work before you put it in the box. The box therefore isn't the problem. You will have to remove it from the box and get it working before you put it back in. I know that sucks, but all you're going to do if you poke at it a bunch right now is break wires and create more problems for yourself. Also, the trauma of removing it from the box after you spent all the time getting it in there will keep you from doing it again.

5. You can narrow down the problem VERY quickly with an audio probe. All you need to build one is an old patch cable and a capacitor.

[dropanchor812]

Hoodoo -  I checked that cap and I think its the right one.  Does it matter that its a ceramic disc cap?  I will have to double check the code on it later, but my build is identical (except the enclosure and switch type) to a build of this pedal that diablochris6 posted a couple of weeks ago.  We ordered the same parts together.  Referencing his picture, it looks to be the same.

Midwayfair - I did read that troubleshooting guide and before I yank the whole thing out I wanted to see if someone might have some obvious insight into the issue that I just was totally missing due to inexperience.  I can check voltages tonight and post them later if it will help.  Yanking everything out is a last resort, but in the back of my head I am kind of figuring that it is what I will have to do.

Here is a link to the BOM and Schem - https://docs.google.com/file/d/0B46z2J0FljLkeVpTMnVmeFJiU2s/edit?pli=1

And as I said in my first post, when I audio probed the circuit I was getting a signal at a normal volume at the beginning of R1, but the right side of R1 was silent. I can't seem to get a straightforward answer from searching around different troubleshooting guides, but will a faint guitar signal pass through a bad resistor?  Would bad wiring make only a faint signal come through?  The faint signal doesn't cut in or out when I wiggle gently on the input wire.     

Since last night I reheated (and gave it a little more solder) both sides of R1 in hopes that a cold solder joint was the problem, but that didn't help.  I can post voltages tonight, but I really feel like R1 is the issue...   

[midwayfair]

R1 is a pull-down resistor at the input.

Check the schematic. One side is connected to the audio input, the other side is connected to ground. What should you hear when you probe ground? What should you hear when you connect to the audio input?

I can help walk you through the schematic, but you should try to figure out some parts on your own first. So let's do that. What do you see as the critical places to audio probe? Can you identify the audio path?

[dropanchor812]

Okay, so as I understand it, there should be no signal when I touch the probe to ground.  Since R2 is connecting R1 and C1, I should be getting an audio signal going through R2 on both sides, correct?  This would confirm what I feared to begin with, that I may have scratched away a trace that would connect R1 and R2.  Maybe I am understanding that wrong.

So I've got the pedal here in front of me and just probed R2.  I get a high pitched squeal when I probe that resistor.  The left side is a higher frequency squeal.  I probed C1 and I get the same squeal on the top lead as I do with the right side of R2... I honestly really don't know what to make of that.  You guys don't have to feed me the answer, but I would appreciate a general direction to run in.  Troubleshooting has taught me more than all of the beginner FAQ's I've read.

And the hum I mentioned in the first post is just the volume of the pedal, I think.  It's not like an annoying weird hum that comes out when there are grounding problems.  Just wanted to clear that up.  Thanks again!

[saxoftenest]

Before you do anything else, I would pull it out of the box and reflow all the joints. The ones I can see look a bit starved, so you may want to add another touch of solder.

Some questions:

Do you have a digital multimeter?
Is it dead silent when you touch the audio probe to ground?
What charge pump are you using?
What's the code on the part you used for C8?
What transistors did you use and did you make any deviations from the BOM?
Can you post some pics of the underside of the PCB?

[midwayfair]

I may have scratched away a trace that would connect R1 and R2.

I say this a lot: Don't guess or trust your eyes. Your eyes don't know what they're talking about! If you suspect a connection is not made, or if you think there might be a solder bridge, use your multimeter. It has a continuity setting that will beep if there's a connection.

[dropanchor812]

Saxoftenest-  Answers:

1.  Yes.
2.  Yes.
3.  I used the one listed on the BOM
4.  Y5P 562k <- ceramic disc type from Mammoth
5.  I did not make any deviations from your BOM.  It is stock everything.
6.  I can if I have to. 

Midwayfair - I'll have to check if mine measures continuity.  Mines a really cheap one from Harbor Freight.

[midwayfair]

4.  Y5P 562k <- ceramic disc type from Mammoth

Cap markings:
http://www.elecraft.com/Apps/caps.htm

[dropanchor812]

4.  Y5P 562k <- ceramic disc type from Mammoth

Cap markings:
http://www.elecraft.com/Apps/caps.htm

Well, bust my bumpers (parents with kids who are Thomas the Tank Engine enthusiasts will get the reference).  Looks like I did make a substitution!  Alright then, I guess its coming out.  Would a wrong value at C8 explain the problem or is that just going to be another problem I need to fix anyways?

[midwayfair]

4.  Y5P 562k <- ceramic disc type from Mammoth

Cap markings:
http://www.elecraft.com/Apps/caps.htm

Well, bust my bumpers (parents with kids who are Thomas the Tank Engine enthusiasts will get the reference).  Looks like I did make a substitution!  Alright then, I guess its coming out.  Would a wrong value at C8 explain the problem or is that just going to be another problem I need to fix anyways?

There are going to be other issues. This is just one, and not a super major one.

[diablochris6]

FWIW, my C8 is the same as dropanchor's. The parts were either mislabeled or misordered, and we were to dopey to double check. My pedal works fine.

[saxoftenest]

I'd do the following:

Unbox it
Replace C8
Reflow all joints
Test for continuity between R1 and R2, and let us know the results
Post voltages from all pins of the transistors
More pics: top and bottom of the PCB, and close ups of anything you may think is suspect

[dropanchor812]

Alright.  So this is what I had time to do tonight...

1.  I halfway unboxed it so that I could get all around the PCB easily... the switch, LED, and jacks are still attached to the enclosure. 
2.  Reflowed joints and added some solder to those that looked a little thin.
3.  Tested it out after that and nothing has changed.
4.  Checked voltages of all the transistor pins.  They are as follows - (Read D-S-G)
Q1 - 8.26 - 0.56 - 0
Q2 - 11.91 - 0.33 - 0
Q3 - 11.26 - 0.56 - 0

I biased the transistors when I first boxed it up and they may have gotten a little jostled around since then, if that matters for the voltage readings. 

I don't have a 68n cap right now so that will have to wait.  If Chris's works with that cap then I'm satisfied to just getting it working with that one in there if possible... for now. 

I also can't check continuity with my DMM.

Here are some pictures of the solder-side of the board after I reflowed the joints.  Thanks for all your help, ya'll are the bestest.