Debugging A Rebote Delay 2.5

[JObscure]

Hey guys,

I've built a Rebote 2.5 using a verified veroboard layout from SabroTone. It has worked on my breadboard, and it also worked fine when I hooked up the soldered board to power and pots to test it. But now that I have soldered the pots and everything else to the board I only get my guitar's sound coming out of the amp with no delays.

1. Name of the circuit:
Rebote 2.5 Delay
(URL of schematic or project) = tonepad.com

2. What does it do, not do, and sound like?
a. Works in true bypass
b. Only guitar sound when on, no delays.
c. Guitar strummed loudly does not induce any sound
d. Twisting the circuit and checking for loose connections did not help.

4. Any modifications to the circuit? No

5. Any parts substitutions?
51pf = 47pf

6. Positive ground to negative ground conversion? No

7. What is the out of circuit battery voltage?9.0V

Voltage at the circuit board end of the red battery lead = 9V
Voltage at the circuit board end of the black battery lead = 0V

IC1 - PT2399

1 - 5
2 - 2.1
3 - 0
4 - 0
5 - 3.8-4 (jumping around)
6 - 2.5
7 - 3.6
8 - 0
9 - 2.5
10 - 2.5
11 - 3.7
12 - 0.5 ish
13 - 1
14 - 4.95
15 - 2.5
16 - 1.2

IC2 - TL072

1 - 4.45
2 - 4
3 - 3.3
4 - 0
5 - 0.4
6 - 0.4
7 - 4.4
8 - 9

Help would be appreciated!

[JObscure]

I have seen elsewhere that the PT chip could be dead. 

Any comments? Anyone?

[gcme93]

This happened to me when I built a Little Angel Chorus and my problem was this:

I had the ground of both cable jacks on the shield (makes sense, as this makes the big metal enclosure your circuit ground). However, I had a metal 9V power plug which had +9V on the shield, and ground in the middle.

This is easy to check with a cheap multimeter, by unplugging all power, and checking that there's very close to zero resistance between the shields (mine comes up with 0.7~Ohms, probably a systematic error in how its measured). All the outside shields should be connected to ground!

Quite an easy mistake to make for a beginner like myself, and possibly yourself?

[bluebunny]

I have seen elsewhere that the PT chip could be dead. 

Any comments? Anyone?

If it's dead, it's probably getting pretty warm.  Your voltages look reasonable (to me, at least), but have a feel of the PT2399.

[JObscure]

@gcme93: I am certain that all grounds are correctly connected, if they weren't then I would not be getting any sound.

@bluebunny: The chip is not getting warm. 

[deadastronaut]

if it worked on breadboard, and when you tested it,....then you soldered the pots,  i suspect its pot wiring....double check those.

[gcme93]

Sorry, misread that one! could you post a photo of how its mounted in the box?

(another silly thing I've done in the past, is had it all fitting in so tightly, that the tip of both input and output were touching the metal surround of the stomp switch core, providing me with true bypass, or true bypass  Not my cleverest moment, but I was so desperate to fit it in that tiny box!)

[JObscure]

Sorry gcme I guess I was not clear enough. The circuit is wired up but not in a box yet.

I have quadruple checked the pot wiring.

[jasonsguild]

Are those IC voltages with the chips in the sockets or out?  If in they are in the sockets then the readings seem a bit off too me.  I just built a d'lay, which is very similar to a rebote, and my voltages were a lot different, especially compared to your readings for pins 7-16.  Also, if you have an audio probe, you can quickly check at pin 15 to see if dry signal is making it's way into the PT2399, and at pin 14 to see if delay sound is making it's way out of the chip, to help narrow down what section the problem might be coming from.

[JObscure]

Are those IC voltages with the chips in the sockets or out?  If in they are in the sockets then the readings seem a bit off too me.  I just built a d'lay, which is very similar to a rebote, and my voltages were a lot different, especially compared to your readings for pins 7-16.  Also, if you have an audio probe, you can quickly check at pin 15 to see if dry signal is making it's way into the PT2399, and at pin 14 to see if delay sound is making it's way out of the chip, to help narrow down what section the problem might be coming from.

Readings are with the ICs in the sockets.

I get sound at pin 15 but none at pin 14. I am starting to suspect a dead PT chip...

[jasonsguild]

Certainly could be a dead chip, especially with that high voltage on pin 14.  If it was me, I would triple check the board to be sure that there are no solder bridges or part mix-ups that would cause a new pt2399 chip to also go dead once popped into the socket.

One more question for you, is the PT2399 oriented in the socket correctly, it's not upside down?  This may be silly, but I put chips in upside down all the time.

If you do go with a new PT2399, order a few, I had to go through a bunch of them until I found one that wasn't noisy or trying to be a motorboat.

[JObscure]

pin 14 is now 1.8
13 - 2.5
pin 5 is still jumpy


All the parts and the layout is/are correct. I'll check over it once more then get a few more PT's.

[bluebunny]

pin 5 is still jumpy

I think pin 5 will always be jumpy: it's a clock out, if I remember correctly...  (And it's not used, i.e. unconnected, in every circuit I've ever seen.)

[JObscure]

Gonna be getting a couple of new PTs tomorrow. I will update whether it solves the problem or not.

[JObscure]

*UPDATE*

Problem turned out to be faulty pots, going to get replacements soon. My supplier is going to hear about this

[deadastronaut]

bummer, i thought it was a pot issue , but on the plus side, you know what the problem is now...



when i first started building i ruined many pots by overheating them...  tin the wire and the lugs , then solder. better/quick connection, less heat.