Rebote 2.5 Delay Debugging Help!

[jwhtn]

Hi, guys.  This is my first post, and I'm very glad I found this forum.
On to business:  I'm building a Rebote 2.5 Delay from Tonepad (http://tonepad.com/project.asp?id=51) and I'm having some trouble.  This is my 4th project (after successful tries with a distortion box and two types of APC), and the first time I've had to troubleshoot, so please bear with me.
Symptoms:  When the effect is bypassed, I get perfect tone.  When the effect is engaged, I get nothing.  If I bypass the first handful of components with an audio probe(inputting right after the second 510k resistor(see pic)), I can get a very healthy delayed sound. 

I've checked out and replaced the components between the input and the point where the audio starts working, which hasn't helped.  Also, I'm only getting a proper sound at this insert point when using a very strong signal (soundcard headphone out),  and I get only the faintest dry sound when plugging a guitar into this point.

Substituted components:
15k resistor changed to 10k (for endless repeats)
5pF cap changed to 4.7pF
51pF cap changed to 47pF
510k resistors changed to 560k (did not work with original 510ks either)

I'm using Offboard Wiring Scheme 1 (no DC jack, no LED, DPDT switch).

Voltage at the IC pins:

IC 1   
   
1   5
2   2.5
3   0
4   0
5   2.38
6   2.5
7   0.06
8   0.7
9   2.5
10   2.5
11   2.5
12   2.5
13   2.5
14   2.5
15   2.5
16   2.5
   
   
IC 2   
   
1   8.21
2   8.12
3   8.35
4   0
5   6.76
6   1.35
7   8.18
8   8.8


The battery is putting out 9.1v.

I'm baffled, but I'm pretty new to this whole thing, so I'm sure there's a electrical concept that I'm failing to grasp.

Thanks in advance for your help!

[Zben3129]

This is just a quick reply, as I don't have the schem out, but IIRC there is a pin (5? I think) that is a NC, and not a connection to ground. make sure you have that. That is the only thing i can really think of right now (tired, no sleep last night)


And welcome!

Zach

[Zben3129]

What do you mean by bypassing with an audio probe and working insert point? Do you mean you are putting the guitar input to the "working insert point" and getting a good sound at the output of the pedal?  Or do you mean you are putting the guitar input in the input jack and using an audio probe at the "working insert point" and getting a signal there.

Zach

[jwhtn]

Hi Zach, thanks for your help.
As to your second question... I mean I am applying a signal (software drum machine) to the circuit at the circled point, and I'm getting a signal out of the circuit's output jack.  I suppose this isn't debugging protocol, but I was just seeing what I could figure out
As to your first reply... I'm not sure what you mean by pin 5 having an NC.  Is this "No Current" or "No Connection?"  Sorry, I don't know the jargon yet.  I should have mentioned that I printed and etched the board for this project, from TonePad's pdf, so I assume the circuit has the correct routing.

-Joel

[Zben3129]

NC means no connection, and seeing as you are using a pcb then that will be correct.

Since, when those first few parts are bypassed the circuit works (does it work fully?) that would indicate a problem there. Check for shorts from anywhere on that blue trace up to the working point to any other trace (solder bridges).

Also, do you have a multimeter? If so, could you measure the resistance across the 1m resistor? Put one lead of the multimeter on one leg of the resistor and the other lead on the other leg. The effect shouldnt be on when doing this, and no signal needs to be applied. If you accidentally put a 100 ohm, 1k ohm, or 10k ohm (maybe even 100k) resistor here by mistake you could be losing your signal to ground that way.

Zach

[jwhtn]

Okay... The 1M resistor reads as 1M, so that's not the issue.  I don't see any solder bridges.
Out of curiosity, I used the audio probe in reverse from the first way I described.  This time I connected a guitar to the input and used the audio probe to go out to my amp.  The signal is strong after the first cap (.082uF), weaker after the first 560k resistor, and pretty much gone after the second 560k resistor.
As an aside, after searching the forum for other Rebote delays, someone reported different output voltages on some of the IC pins.  Would poor voltages at the ICs cause the issue?  Remember that the signal (in the audio probe input to output jack output scenario) only comes through if it's very strong.
Thanks!
-Joel

[Zben3129]

Incorrect (drastically, usually more than .4v different-ish) are a good indicator of something wrong. However I still think you may have a problem in the very beginning (you could have multiple problems, everyone's favorite  ). Can you check to make sure the cap that is right next to the second 560k resistor is the correct value?

Zach

[Zben3129]

IC 2   
   
1   8.21
2   8.12
3   8.35
4   0
5   6.76
6   1.35
7   8.18
8   8.8

Pin 3 and 5 look suspicious to me. I don't know the workings of the circuit or the schem, but usually in the dual opamps these are connected to vb, which would be half of the voltage, so in this case, 4.5v. Could you take a voltage reading somewhere on the green/orange (sorry, I'm colorblind [not good for reading resistor values  ]) trace. Put the red DMM lead on the trace and the black lead on ground. Let me know what you get.

Also, pin 1 and pin 7 don't seem right, but I don't remember what these are supposed to be like in opamps. Sorry, I'm still learning 


Zach

[jwhtn]

Zach,
I'm hitting the sack for tonight.  I'll try these things out after class tomorrow night and post the results.  Thanks again!

[Zben3129]

I'm going to bed aswell, once the sox win!! (I hope  )

Go sox.

Zach

[jwhtn]

Hi again, Zach.  It's funny that you mention the baseball game... I was only up so late last night because I had to make sure the Steelers stuck it to the Jags.
Anyway... I've checked the cap next to the second 560K resistor, and it is the 4.7pF that it should be. 
The orange trace reads 8.6v (the battery is putting out 8.8v today).
And I verified the readings on IC2, and they are what I first reported.
Here I was hoping it would be something obvious!
Thanks,
-Joel

[Zben3129]

hmm, could you measure the resistance across each of the 12k resistors to the left of the "working insert point"

[jwhtn]

Those resistors check out as 12k.  In fact, I just metered every resistor on the board, and they're all apparently correct.

[Zben3129]

hmm...

Could you check for any solder bridges between the red trace and the orange trace? Reason being that the orange trace should be at about4.5v and its 9v, making me think there is somehow a short between the 2

Zach

[jwhtn]

Hi, Zach.
I will check that out when I get back from class tonight. 
Meanwhile, is there a brief explanation of why the orange trace should read 4.5v?  I'm hoping to gain some understanding of the theory.  I see that the orange trace is separated from the red by one 12k resistor, and that the red trace hits pin 8 of IC2 while the orange trace connects to a 1k resistor and then hits pin 3 of IC2.  And for that matter, why is the orange trace orange?  Argh, there's so much I don't know!  Thanks!

[jimosity]

The first thing I would do is use a continuity tester to test your traces to ensure that they are all good.
One tiny, unvisible to the naked eye issue with one of my etched boards had me pulling my hair out.
Also, maybe try a different wrapper to see if that can help you out, just changing to a different wrapper once solved an issue with a Rebote 2.5...

If you can take some really good pics, maybe we can help more...

[Zben3129]

>Why should the orange trace be 4.5v

  This trace is the Vref trace, which is half (4.5v) of the Vcc Voltage (9v). This is used for biasing reasons. Rather than try to explain it myself, this thread  http://www.diystompboxes.com/smfforum/index.php?topic=60335.0   

>Why is it orange?

Just to make it stand out from the rest to make the layout easier to read.


Zach

[jwhtn]

Thanks guys.  If I haven't drunk myself into a stupor by the end of the debate, I'll set about testing continuity tonight.
Thanks again!