Delay pedal: one of the pots doesn't seem to work

[THE-ElBaRtO]

Hello everybody,

I just finished the Mad Professor Deep Blue Delay pedal effect using this schematic http://tagboardeffects.blogspot.fr/2012/02/mad-professor-deep-blue-delay.html (the original version one) and it works like a charm except for one thing:

When I play a note it only repeats once, no matter if the Repeat pot is at 0 or all the way to the max. I made sure that there was no problem coming from the pot itself with a multimeter and it seems to work just fine.

Here are a couple photos of the wiring.

Thank you for your help

[Zanius]

As far as I can see from your pics, your wiring looks good. If you are sure your pot doesn't somehow touch the enclosure (ground) on lug 2 or 3, there is something wrong on your board.

The most likely reason is a short on your board, a forgotten cut or a misplaced component.
Direct photos of both sides of the board would be a great help.

[THE-ElBaRtO]

Ok I don't know how but while taking the pictures you asked for I touched some of the wirings and decided to test it and the repeat started working !!! It sounds great I'm really enjoying it, thanks for your help anyway :)

[THE-ElBaRtO]

Well my fun didn't last long, after a couple of days of working fine it came back to the single repeat pattern.
So here are the pictures you asked for:

[Zanius]

Well, since it worked once it probably means that everything is ok on the board (placement-wise). As you said, it worked when you moved something, so check again your wire connections on the board and pots, and make sure nothing touches anywhere it shoukdnt. Some solder points on your board also look suspicious, try putting some more solder on them. Also, I would cover up those naked wires I see around your enclosure.  

[THE-ElBaRtO]

Well I did all the things you recommended me to do but the sound is exactly the same... Could it be that the PT2399 is faulty? Because I directly put solder on the pins and i've heard that it could damage the chip

[Zanius]

Here are some voltages I found (not mine). I think the are correct.
If you want to go deeper you need to measure yours and compare.
I still believe it's just a bad connection though, but if I learned something through debugging is that you should never assume things

PT2399
1 - 5.00
2 - 2.48
3 - 0.00
4 - 0 .00
5 - 3.61
6 - 2.49
7 - 0.57
8 - 0.85
9 - 2.49
10 - 2.49
11 - 2.49
12 - 2.49
13 - 2.49
14 - 2.49
15 - 2.49
16 - 2.49

OP275
1 - 4.42
2 - 4.34
3 - 4.31
4 - 0.00
5 - 4.31
6 - 4.33
7 - 4.31
8 - 8.70

78L05 regulator
I - 8.69
G - 0.00
O - 5.00

[THE-ElBaRtO]

Some of the values are spot on, some others differ from 0.1 to 0.5 maximum (almost exclusively under expected values)
I listed below all off-values:

PT2399
5 - 3.21
7 - 0.70
8 - 0.72

OP275
1 through 7 (except 4) ~ 4.22
8 - 8.31

78L05
I - 8.36
G - 0
O - 5.00
(I think this one works fine because it's a 5V regulator after all)

Are the values differences significant enough to be the problem?

[Zanius]

Your voltages seem fine. The only difference you really have comparing to the numbers I posted is slightly different supply voltage (8.7V instead of your 8.36V), that's why all the other values are slightly off, no worries there.

I'm not sure what readings the 2399 gives when it goes bad though. Let this be a lesson and always use sockets for ICs and Transistors, so you can easily switch them and get it off your mind.

I still think your problem lies elsewhere. When shit hit the fan, I take apart the whole pedal, unsolder all wires, switches and pots, clean them up and start again.

[induction]

If you're getting one repeat, then the PT2399 is working fine. Repeats work by feeding the delayed signal back into the chip input, so the problem must lie somewhere in the feedback path. A dodgy solder joint in the feedback path or a broken wire on the repeats pot would explain the intermittent symptoms.

[THE-ElBaRtO]

That's a relief! I'm gonna take both your advice and Zanius's and remove all components in the feedback path, change all wires going to the pot and solder everything back, I'll let you know if it worked. Thanks guys!

[THE-ElBaRtO]

I'm so mad at myself, I didn't check the pot correctly and it was broken all this time.... That's it, no wire or joint problem, just a faulty pot.... Anyway I don't know why the pot worked fine for a couple of days and then stopped working. At least I've learned a lot of things while trying to repair it! But if you know what could cause this I'd be interested.

Last question: when I use an external power source I hear in my amp this small constant "wind" in the background but if I use a 9 volt battery there is none. Someone got an explanation?

Thanks again

[GrooveChampion]

From personal experience installing the pot the wrong way, tightening its nut too much or tightening the knob around the shaft too much can make a pot go bad.