SOLVED Special OD troubleshoot

[Redspacecadet74]

Hi, I’m hoping for some help troubleshooting the Special OD I just built.

When I first plugged in the pedal I got no sound at all with the pedal switched on or off and the LED didn’t work either. I did a quick check and realised I had the positive wire from the PCB connected to the battery terminal of the power socket instead of the positive terminal. I quickly fixed this and plugged the pedal back in but still no sound or LED. So I did a more thorough check and this time I noticed that capacitor C13 is reversed, i.e. the positive lead is wired to the negative pad on the PCB and vice versa. Other than that everything looks correct to me (the photo below was taken before I retired the power socket).

Before I replace capacitor C13, I was hoping someone with more knowledge of circuit design could tell me if this explains why I’m getting no sound and/or why the LED is not coming on?

 

[Laundryroom David]

I had a quick look at the schematic. Looks like c13 is a filter cap for vref. Do yourself a favour and replace c13 before you try to move more electrons or figure out why the pedal isn’t passing signal or lighting up.

 

[fig]

It's a bit hard to tell, but C8 C12 may be reversed as well.

Edit: Corrected

 

[Redspacecadet74]

It's a bit hard to tell, but C8 may be reversed as well

I think C8 is ok. The stripe (-ive) is on top as you look at the photo, which aligns with the circular (-ive) pad on the PCB.

 

[Redspacecadet74]

Hi, I’m hoping for some help troubleshootping the Special OD I just built.

When I first plugged in the pedal I got no sound at all with the pedal switched on or off and the LED didn’t work either. I did a quick check and realised I had the positive wire from the PCB connected to the battery terminal of the power socket instead of the positive terminal. I quickly fixed this and plugged the pedal back in but still no sound or LED. So I did a more thorough check and this time I noticed that capacitor C13 is reversed, i.e. the positive lead is wired to the negative pad on the PCB and vice versa. Other than that everything looks correct to me (the photo below was taken before I retired the power socket).

Before I replace capacitor C13, I was hoping someone with more knowledge of circuit design could tell me if this explains why I’m getting no sound and/or why the LED is not coming on?

Sorry, quick correction. I just checked again and it’s C12 that I’ve reversed not C13.

 

[Laundryroom David]

Schematic shows c12 as filter cap for vcc. Same deal. You should replace it before you try to troublehoot.

 

[Redspacecadet74]

Schematic shows c12 as filter cap for vcc. Same deal. You should replace it before you try to troublehoot.

Thanks. I’ll definitely do that.

 

[Redspacecadet74]

I decided to check the polarity of the power LED with my multimeter. I connected the positive lead of the multimeter to the round (anode) pad on the PCB and the negative lead to the square (cathode) pad on the pcb and the LED lit up. So I believe it is orientated correctly. However, when I checked for continuity between the cathode of the LED and the ground terminal of the power socket there was no sound on the multimeter. Is this right, or should there be continuity?

 

[fig]

I think C8 is ok. The stripe (-ive) is on top as you look at the photo, which aligns with the circular (-ive) pad on the PCB.

Sorry, wrong cap. Both C12 & C13 (the two axial caps) appear to be incorrect.

 

[fig]

I decided to check the polarity of the power LED with my multimeter. I connected the positive lead of the multimeter to the round (anode) pad on the PCB and the negative lead to the square (cathode) pad on the pcb and the LED lit up. So I believe it is orientated correctly. However, when I checked for continuity between the cathode of the LED and the ground terminal of the power socket there was no sound on the multimeter. Is this right, or should there be continuity?

I believe the round pad is negative (cathode).

 

[Redspacecadet74]

I believe the round pad is negative (cathode).

According to this image the round pad is the anode. I believe on some of the older pedalpcb boards the round pad was the cathode, but these are supposed to have been phased out.

 

[fig]

I was looking at the silkscreen image, so it could be older. @Robert ?

 

[Redspacecadet74]

Sorry, wrong cap. Both C12 & C13 (the two axial caps) appear to be incorrect.

I checked with my multimeter and I think C13 is orientated correctly, but C12 is definitely wrong. It’s hard to tell from the photo because you can’t see which way the arrows on the stripe are pointing…..my fault for using linear rather than radial electrolytic caps!

 

[fig]

I checked with my multimeter and I think C13 is orientated correctly, but C12 is definitely wrong. It’s hard to tell from the photo because you can’t see which way the arrows on the stripe are pointing…..my fault for using linear rather than radial electrolytic caps!

Cool. Sometimes you have to use what you have.

 

[Nic]

I was looking at the silkscreen image, so it could be older. @Robert ?

Almost certain that newer design all use square for cathode for the LEDs. There is a thread somewhere about that and the various silkscreen design used. I went all square to anode on my second built a few months back and wondered why the pedal did not work ... it in fact worked, just not the LED

 

[Locrian99]

Almost certain that newer design all use square for cathode for the LEDs. There is a thread somewhere about that and the various silkscreen design used. I went all square to anode on my second built a few months back and wondered why the pedal did not work ... it in fact worked, just not the LED

I finally took a screen shot of that thread. I seem to mess that up every time.

 

[Robert]

The LED pads are generally marked on the silkscreen so you don't have to try and remember the shapes.



A - Anode
K - Cathode (Kindly remember the ridiculous nomenclature is not of my making)


There are still a few oddballs roaming around that have not been marked, but most are these days.

 

[Redspacecadet74]

Well, I’m happy to say, I replaced the electrolytic capacitor I had soldered incorrectly and the pedal works. I’m pretty pleased with how it sounds too. Only tried it with my small Yamaha TR10 practice amp, looking forward to trying it with some proper valves.

Thanks to everyone for all the help and suggestions.