Yellow Shark: LED & Bypass Work, No Effect

[whitebread47]

I populated this etched board over a month ago, it didn't work and am just now getting to troubleshooting it.  Indicator LED and bypass work fine, but there is no effect when engaged.  I've now quadruple-checked the wiring, everything looks good.  I will continue checking, though.  I can't find any cold solder joints or traces, but ran a pick through just to make sure.  I'm getting GND continuity and 8.95v to the center pin of the DC jack.  No substitutions were made for the components, and I've triple-checked values for good measure.

I did accidentally lift off the negative lead LED and SW pad, so I soldered those respective leads to each other since the trace between them was connected and isolated as well, so I don't think this could cause a problem since the switch and LED appear to be functioning properly.  The clipping LEDs are not lighting up at all.

Now for voltage readings.  Here's what I'm getting on the CA3130EZ:

1 = .07    8 = 4.26
2 = 4.10  7 = 8.25
3 = 2.95  6 = 4.11
4 = 0.00  5 = 0.00

From my limited understanding (and reference to the datasheet) this looks pretty close to what it should be (I think input should be around 4.5v and output around 9v?).  Please correct me if I am wrong, however, as I'm used to dual opamp readings.  Since pin 4 is V- and pin 7 is v+, should I be getting -8.25 at 4?  On the schematic, both 4 and 8 go to ground, so I'm a little confused on how voltages should read here. 

Also, the drain of the 2n5457 is getting 8.19v.  My uneducated guess is that I may have a grounding issue, though I can't seem to find where.

I have to step away from my workstation to run an errand, but I will take some close-up pictures when I return.  Thanks in advance for any suggestions or tips!

[jkokura]

Pictures of the wiring would help. Have you got an audio probe? That will help a lot.

Jacob

[whitebread47]

That errand took longer than planned, sheesh!  Happens with women, I suppose.  Anyways, here's some photos of my wiring and my amateur PTP solution for the SW and - LED pads.  This was the first etched or single-sided board I'd done, so it's not very pretty. 

I have terrible lighting here, so some of those joints may appear cold, but they are all shiny in person.  Let me know if there are any specific things I need to take close-ups of, thanks. 

Also, I do not have an audio probe, but am thinking I'll build your testing rig w/ audio probe tomorrow with my free time.

[whitebread47]

Any ideas of what to look for?  I've exhausted my limited knowledge here! 

[whitebread47]

A little added information:  I was reading R.G. Keen's article about debugging non-working builds and discovered that taking a voltage reading of any zener diodes (if present) is a good idea, so I followed suit.

I am getting 5.53v at the anode and 8.34v at the cathode.  I'm still not quite sure what that means, but figured it would be worth adding here.  Tomorrow I will be building the audio probe as described in jkokura's sticky, so maybe that will help me find the problem.  As always, I'm here to learn, so feel free to school me if so inclined.  I'd rather not create these threads if I can find the solution myself. 

[whitebread47]

Okay, I think I may have located the problem.  I've followed the copper traces along with the schematic, which served as an extra part orientation/value check and helped me know where the circuit appears to be working.  I took voltage readings of all the diodes this time and that D3 & D4 are not getting any voltage.  They appear to be in some kind of ground loop (I'm assuming that's what that is on the schematic).

Since I am getting 4.11v out from pin 6 on the IC, it appears I'm losing signal before these diodes.  Also, both pin 1 & 5 being offset nulls, shouldn't they read the same?  If so, 0.07v is leaking into pin 1? Pin 5 is 0v.  I checked to see if I had a bad opamp by replacing the CA3130EZ with a TL071CP (referenced the datasheets), but still get the same result.

I haven't been able to build the audio probe today, as I seem to have misplaced some of the needed materials (test lead, alligator clips for test rig).  I feel like I'm getting closer to finding the problem, but don't know where to go from here!

[jkokura]

At this point, your voltages and wiring aren't helping to lo ate, thre probe is what you need.

I'd start at the output and walk backwards to see if we can find the problem.

Jacob

[whitebread47]

I'll track down the materials and put one together and follow your suggestion, thanks.

[oldhousescott]

Your chip voltages look OK. You won't read any DC voltage at D3 and D4 since they're grounded on one end, and isolated from any other voltage by C6, C7, C8, C9, and C10. D3 and D4 will limit the audio signal to about +/- 0.6 volts (AC about zero). Q1 should boost the signal back up a bit before sending it to the volume pot. You need to get that audio probe put together.

[whitebread47]

Alright, so I built an audio probe using a design I found on diystompboxes.com since I did not need the entire testing rig at the moment.  It works fine, but I still can't figure out what is wrong with this circuit.

I started at the output, since I know everything up to the transistor is working, and worked my way back to Q1.  I probed all the sections of the circuit for good measure.  I get an overdriven signal right up to this point.  Basically, the entire output section is not getting signal.  Though the joints all looked good and I saw no visible bridges, I reflowed each joint in the output section and picked between the traces; still nothing.

I do have a couple of questions.  Is it possible that I have a bad volume pot, and would that cause the output section to fail?  Other than two caps and a resistor it's the only part that I could see being possibly faulty in this section.  The other passive components there are nopolar and of correct value. 

Perhaps I am misunderstanding the schematic, but I think I'm reading it correctly.

[jkokura]

Where specifically does your signal stop? That's where we need to focus.

Jacob

[whitebread47]

If I probe from the output backwards, the first place to get signal is the drain of Q1.  Sorry, it is the gate that I first get signal.

[jkokura]

I would suspect either that you're not getting power to the 2N5457, the transistor is backwards, or it's bad. Have you got another? What are your voltages there?

Jacob

[whitebread47]

Yes, I have a handful of them.  It's oriented correctly, unless different brands use different pinouts on those.  I only referenced the Fairchild datasheets, so I'll check the manufacturer on mine for good measure.  I'll take voltage this afternoon as soon as I get the chance.

[mgwhit]

Data sheet pin out diagrams have fooled me before.  They're usually oriented as if you were holding the transistor upside down, not looking down on it from above.  May want to double check.

Edit: I just looked at your photo and the orientation looks fine.  I should've checked first.