Build Your Own Clone Message Board

Hi, this is my first build and everything originally was going great and the pedal was working. I then went and swapped out the LED as I'd soldered it in too close to the board so it wasn't popping out of the case - bad idea, as now it doesn't work. The LED comes on and bypass is fine, but I get no response from the pots - no effect. I have tested all the connections and de soldered all the off board wiring and re soldered it all and tested it again - twice. Everything is connected and there are no dry solder joints. I don't have access to a camera right now as my girlfriend has it on holiday so I was just hoping for someone to shed some light on the readings I obtained from it.

While connected to a 9v power source I put my black probe from my MM to ground (first the screw holes of the enclosure and second the ground connection on the input jack). My first lot of readings gave me 0's for every leg on the OPamp and the Optocoupler. When I tried with my ground probe at the input jack every reading was above 8v - that is for each leg of the OPamp and optocoupler. I then put my black probe to the ground on the output jack and got readings of 0's again.

I went on to try this without a 9v power source and got 0v readings for everything - not sure if I had to do this but thought I should anyways. It might be worth mentioning that I burn't the top of a 0.01uF cap while replacing the LED - the top is slightly caved in by the heat of the soldering iron - could this effect the EFFECT?

I'm not sure what else I can test - I tested all the pots before putting them in and they were fine - every connection was tested throughout the process and again at the end - all solder joints have been checked, re checked and checked again. Wiring was followed as per instructions and checked again and again and again. If anyone needs more info I will post more - also pictures may be possible with my phone camera however its resolution is poor and I think that to see any detail from the pictures just wouldn't happen.

1) Did you remember to insert a plug into the INPUT jack to turn the circuit ON before taking your measurements?

2) Possibly but MANY people have done this without damaging the caps bad enough to cause them to fail.

3) I would check continuity of your wires from one end to the other. Often times when the board is removed to make a repair or alter something a wire can break somewhere resulting in the pedal no longer functioning when it did before.

If this doesn't help post photos as soon as you can. Be sure to include shots of both sides of the PCB as well as shots of the wiring. Make sure the photos are up close and in focus. Blurry photos are pretty much useless. We need to see as much detail as possible. Try not to post photos so big that they need to be displayed on a flat screen TV to see the entire image in a single view.

Hi, thanks for the quick response - this is my first build and as you can probably tell... I didn't have an input going into the pedal... my readings are as follows...

Receiving 9V DC to input AND to 9V pad on the circuit board

Op amp

1 = 4.16
2 = 4.16
3 = 3.36
4 = 0.00
5 (directly opposite 4) = 3.54
6 = 3.88
7 = 4.14
8 = 8.31

Optocoupler

The side with 2 legs:
Positive pin (+) = 0.03
pin next to positive = 0.00

The side with 3 legs:
Reading from directly underneath or opposite + pin (depending on which way you look at it, going right -> = 2.86, 3.36, 4.11

Your voltages are a bit off in a few places. Here's what I got from mine.

Op-amp
1) 4.18V
2) 4.19V
3) 4.17V
4) Ground
5) 4.12V
6) 4.19V
7) 4.17V
8) 8.38V

Opto-Coupler
LED+ 1.4V
LED- Ground

Left to Right
1) 4.17V
2) 4.18V
3) 4.18V

I will double check when I get in from work - it may have just been that I was a little rushed when checking and took the first reading rather than an average reading. Do you think the problem could lie in the + leg of the optocoupler? I get a reading of around 0 - 0.04 which is quite different to 1.2-1.5... I have also made an audio probe but I'm a little unsure what I'm doing with it... Do I just go from input and follow the 'route' of the circuit making sure there are connections... If I hear no sound after a point where there was sound I take it that is the source of the problem? I'm going to have a big crack at it tomorrow. Thanks for being patient.

Jonny.

With your signal probe do the following checks...

You should have signal at both ends of C1, R2 & R3.

You should have signal on the left side of R7. When you pluck a string with the probe on the right side of R7 you will get a squealing sound. You will also get the squeal at pin 2 of the op-amp. Don't have your amp turned up very loud for these squeal tests.

With the toggle switch set to AUTO mode place the probe at pin 1 of the op-amp. You should get a wah sound here. You should then hear the wah sound on both sides of C4 & C5.

Next go to pin 5 of the op-amp. Here you should get your normal guitar sound. You should also get the same sound at pin 6. At pin 7 of the op-amp you will get a much louder guitar sound.

The signal should now be at both sides of C7. You should next hear your guitar at the bottom of diodes D1 & D2. You should hear a distorted sound at the top of D2. You should also have this distorted sound at the bottom of R13. The sound at the top of R13 will be much lower in level. This same sound will also be at the wiper of the LEVEL pot as well as the left lug of the toggle switch. It will also be at the center lug of the toggle switch when it is set to AUTO mode.




Here's an update on the voltage for the Opto-Coupler's LED. With the toggle switch set to MANUAL mode you should have about 1.5V on the + lead with the MANUAL knob turned fully CCW. With the knob set fully CW you should have about 1.4V at the + lead. With the toggle switch set to AUTO mode you should have about 0.8V at the + lead regardless of where the MANUAL knob is set. Since your voltage wasn't near these values check to make sure you have a 10K resistor at R16.

Hi again, thanks for such a detailed explanation of what to do - I have done all the checks (got my brother to play guitar while I poked about)... I found NO wah sound at all on pin 1 of the OpAmp or anywhere I probed. The optocoupler gave yet another reading of 0.04-0.07 volts at the positions described by you. I'm thinking the problem lies here and maybe because this is not fully functional it is effecting the wah response at pin 1 of the OpAmp. I'm going to search into what it is an optocoupler actually does and hopefully this will provide some insight. I'm sure I heard somebody, maybe it was DVM say that it was the heart of the envelope filter though so it would make sense that if this was out it could be affecting the whole circuit. I tripple checked to see whether there was a 10k resistor next to the opto at R16 and there was. The pedal actually started out fully functional so it's safe to assume all the components are in the correct place.