Please help: troubleshooting the MXR Blue Box

[tommycataus]

Hey guys, me again...

I was wondering if you might be able to help me understand what should be happening in my circuit and why it is not working properly.

I recently decided to build the MXR Blue Box based on a vero layout (sorry to you non-vero guys!) on the Sabrotone website. I breadboarded the circuit successfully, but having soldered the vero I am getting some strange results and I can't identify what has gone wrong.

The output pot works fine. The blend pot is pretty quiet on the octave side, but when rotated gives some distortion. This is interspersed with a regular clicking which makes the whole effect sound akin to a wet fart - useful for some people, I'm sure, but not the result I was after!

I would really like to understand what is happening here, whether the voltages are correct and what I can do next to try and understand. I believe it is the CD4013 IC that is responsible for the octave effect, but being at the same intelligence level as a village idiot, I am unable to identify any issues in that area of the circuit.

SCHEMATIC:
http://www.tonepad.com/getFile.asp?id=73

Sabrotone's layout:



And here is my attempt:





I've traced the circuit and I can't see anything out of place. I've also re-melted all the connections and checked for shorts and dry joints. No progress, either forwards or backwards.

Voltages are as follows (source voltage 9.07V).

4558

1 - 4.55V
2 - 4.51V
3 - 4.10V
4 - 3.00mV
5 - 4.57V
6 - 4.55V
7 - 5.06V
8 - 9.07V

CD4013

1 - 4.53V
2 - 4.53V
3 - 4.53V
4 - 0.60mV
5 - 4.53V
6 - 0.50mV
7 - 0.80mV
8 - 1.40mV
9 - 4.53V
10 - 1.00mV
11 - 4.39V
12 - 4.53V
13 - 4.53V
14 - 9.07V

As always, any help would be greatly appreciated Thanks so much in advance!!

Tom

[Seljer]

Get us the transistor voltages too!

[tommycataus]

Ooops... my bad!


Q1:
C - 4.27V
B - 0.468V
E - 0.4mV

Q2:
C - 3.44V
B - 387.8mV
E - 0.4mV

Q3:
C - 7.03V
B - 1.7mV
E - 1.6mV

This is exactly what comes up - I'm using an auto-ranging DMM. These look more out than the ICs... am I right?

Perhaps I should try and debug this on the weekend... 

[kaycee]

Does your number of track cuts tally?

Not sure of your orientation of D1?

Pin 4 of IC 1 should be ground, so not sure that you should be getting a voltage reading there for this build. Likewise voltage on the ground pin of IC 2, pin 7. Use the continuity function of your meter to check that you have ground connections at these points, then make sure that you haven't got a short from the ground lines around the IC's to adjacent lines.

[tommycataus]

Thanks kaycee, the diode was right as were the cuts. I checked the continuity and no problems there... so I  reseated the ICs again and re-melted the connections, and it works. Don't ask me where the short was - it just goes to show that if you test everything, debug it and it doesn't work, try again.

I think I've been overdoing it to be honest, new job and all... I'm going to focus on finishing enclosures for a couple of weeks and give my brain a rest.

Thanks guys!
Tom