Mobius Trip Looper Debugging thread

[Duane90]

Hello all!

I'm not new to this forum but this is my first post. I've been building stompboxes and other gadgets for over a year now and I'm loving it. I have succesfully built different kinds of effects and naturally I've also learned alot from the mistakes I've made. Thanks to this forum and other resources on the internet I've been able to identify and fix the problems I had. So thank you!

But I'm currently trying to get Dean Hazelwater's Mobius Trip Looper to work. I have honestly read every possible text regarding this build but I couldn't find the solution. I also know that I'm not the only one with the same problem. This thread is also a compilation of the information concerning this project/problem.

Here's the the debugging form filled:

1.What does it do, not do, and sound like?
I can get the guitar signal through but it won't record/play. Both LEDs work as they should be. Dry pot works. It's just the recording and playbacking that's not working.
2.Name of the circuit = Mobius Trip Looper
3.Source of the circuit (URL of schematic or project) = http://www.generalguitargadgets.com/projects/28-other-projects/147-mobius-trip-looper
4.Any modifications to the circuit? Nope. I used the switching method by idiot_savant
http://i4.photobucket.com/albums/y130/idiot5avant/schematics/looper-bypass.jpg?t=1256711620
And this wiring diagram by loves_guitar
http://farm3.static.flickr.com/2804/4452639459_584d7fdba4_o.png
5.Any parts substitutions? I used the ISD1020 instead of ISD1000. But it has been reported to work as well.
6.Positive ground to negative ground conversion? No
7. Voltages

Battery 9.09V

IC1 (ISD1020)
1. 0V           15. 0V
2. 0V           16. 5V
3. 0V           17. 1.48V
4. 5.0V        18. 1.48V
5. 0V           19. 1.48V
6. 0V           20. 1.48V
7. 0V           21. 1.61V
8. 0V           22. 0V
9. 5V           23. 5V
10. 5V         24. 4.77V
11. 0V         25. 5V
12. 0V         26. 0V
13. 0V         27. 5V
14. 0V         28. 5V

IC2 (4001)
1. 5V           8. 5V
2. 5V           9. 5V
3. 0V           10. 0V
4. 0V           11. 0V
5. 4.77V      12. 5V
6. 4.77V       13. 5V
7. 0V           14. 5V

IC3 (TL072CP) U3 on schem
1. 5V            5. 5.03V
2. 5V            6. 5.03V
3. 4.98V        7. 5.03V
4. 0V             8. 7.41V

IC4 (TL072CP) U4 on schem
1. 5.03V        5. 5.03V
2. 5.03V        6. 5.03V
3. 5.03V        7. 5.03V
4. 0V             8. 7.39V

D1
A = 0V
K = 4.77V

D2
A = 5V
K = 4.77V

---

I read about the missing jumper and capacitor. There should be a 0.1uf capacitor between 28 & 12 and 16 & 13. In the layout they are using the same cap. In the schematic it's two separate caps. I'm puzzled here.

The layout was missing a jumper between 1, 2, 3, 5, 6 & 26 and ground as shown in the schematic. I added the jumper but it didn't really change anything.

I don't think it's about the 4001 since the LEDs are working.

Here are all the topics I was able to find just now as I'm writing this. There are more but these gave me the most information about this project:
Dean Hazelwanters Mobius Trip Looper build questions
Mobius trip looper at GGG No sound (John Lyons had the same problem and it got fixed. I've no idea how!)
HELP mobius trip looper (Other people having the same problem)
Mobius Trip question
Mobius Trip Looper Problemos (schem errors?)

Thanks to all the people who contributed in those threads. And thanks to Dean as well for designing this!
I would be most grateful if somebody would give me a clue. I know it's a complicated project and there's a lot to investigate but maybe this thread will be helpful to someone else as well

[icculusdividedthesky]

Duane: I am getting the right voltage on all the chips of the isd1020 except for 17 through 21 i am getting 0v. I am new to diy so I am not sure what is going wrong. if there's nothing connected to these pins how are you getting a voltage drop?

[motion2freedom]

I'll check the voltages later, but seems i have the same problem. leds work, dry seems ok, volume knob works and scratchy sound for pots is there, but no looping.

my chip is 1020api, "i" stands for "industrial", which means it should work in a wider temperature range (that's all, according to datasheet). No success with the loophole with this chip either.