Autobahn - something isn't quite right...

[mysticaxe]

So I populated an Autobahn board and fired it up...  Nothing.  Reflow all of the joints and clean up what appeared to be a couple unintentional bridges.  I did lift the traces in a couple spots, but I "fixed" that by using bits of resistor legs to connect the lifted area to the places it was supposed to go and everything checked out by continuity. 

OK, break out the multimeter.

IC1 (LM324) - Pin 4 is at 8.7V, Pin 11 at 0, everything else is at about 4.3V except pin 7 which I've measured at 7v and I've measured at about 80 mV.  Strange thing #1...

IC2 (LM13700) -
1 1.49V     16 1.49V
2 0.44V     15 0.97V
3 1.49V     14 4.3V
4 4.28V     13 4.2V
5 4.3V       12 7.6V
6 0            11 8.7V
7 0.68V      10 7.6V
8 1.7V        9 6.4V

Ground and +V are OK.  Don't know what to make of the rest...

Audio probe -
I have signal up to the C6/R17 junction and nothing on the other side, but I have audio on pin 14 of the LM324 (if the sense pot is wide open, with it "closed" there is nothing at 14).  No audio on pin 13.  Take the IC out (wondering if it is fried), and there is audio on the trace between R17 and the sense pot.  Put a TL074 (don't have another LM324) in its place and I get the same - no audio at pin 13.  With the LM324 in the circuit, the audio is really weak and heavily distorted later in that path (around R20) with a very weak signal feeding Q2.

On the LM13700 side, I have audio to the C2/R5 junction, but nothing past it anywhere on the LM13700.  Haven't tried taking that IC out, because at that point I was a fine mix of confused, frustrated and tired.

Any thoughts?

[mysticaxe]

I also verified all caps and resistors.  No substitutions for transistors.  J201 is passing signal as expected and the voltages look reasonable.  Diodes are all correct per schematic and facing the right way.

[madbean]

You're not going to get any audio from pin 13 with an audio probe. What matters here are the output pins. It should be loud and pretty distorted as it makes its way through the rectifier and such.

Are you using BC550 on Q2, Q3? Have you verified that you are getting 5v output from the regulator?

[mysticaxe]

Yup - the regulator is putting out 5v.  The voltages around the BC550s are (c/b/e):
Q2 - 4.9/1.1/2
Q3 - 4.95/4.3/3.4

I was expecting the base of Q3 to be the same as the emitter of Q2, which it wasn't...

[mysticaxe]

Pictures - I'm still confused...  No audio on the output of either the IC1 or IC2 paths.  Soldering is a little sloppy (the tip on my Radio Shack iron was almost blunt nosed).  I did lift traces in a couple spots, but I either used a bit of resistor leg wire or just solder bridged across and checked for continuity at all spots.

[jimilee]

Pictures - I'm still confused...  No audio on the output of either the IC1 or IC2 paths.  Soldering is a little sloppy (the tip on my Radio Shack iron was almost blunt nosed).  I did lift traces in a couple spots, but I either used a bit of resistor leg wire or just solder bridged across and checked for continuity at all spots.

Go through and make sure all the bridges are supposed to be bridged, sloppy soldering doesn't work well on etched boards. Are the pots turned all the way down? This helps too. This is my favorite auto wah.