MXR Phase 100 - Changed led to a super bright blue. Now I don't get any effect!

[ainokami]

Hi
I just changed the on/off led of my MXR pahse 100...and now that i've put together the pedal again, i dont get any effect.
I checked the pedal again, and i dont see any damage to the pcb board, and nothing but the led was touched by my soldering iron.

what do you suggest I can do to troubleshoot my pedal?

[Xelent]

Is it possible the LED was used as a diode?

[kerloom]

Did you change the color of the LED?
I have done some lab practices where I use a LED to indicate something. For some reason, one time when I changed a red LED for a Blue LED the circuit didn't seem to work. My assumption was that since blue LEDs have a higher voltage (about 3V vs a 1.5 red one) there is a voltage fall that affects your circuit. You would have to check the specific layout of your circuit though.

[Xelent]

That could be it to. The blue LED could have more draw, and starve the circuit, however slightly, of the power it needs elsewhere.

[Processaurus]

That could be it to. The blue LED could have more draw, and starve the circuit, however slightly, of the power it needs elsewhere.

Not how LEDs work.  LEDs are diodes and the current they use (as an indicator light in a typical pedal) is set by their series resistor.  Changing the LED and not the resistor feeding it current shouldn't change the amount of current (maybe a little because blue LEDs have a ~2.5v-3v voltage drop vs. red's 1.4v, but that would make it take less current, not more).  Also in most pedals the indicator LED circuit is in parallel with the effect, so it is fairly independent and shouldn't affect the power the effect is seeing.

The Phase 100 (just had one apart coincidentally) uses a dpdt stompswitch in the "tone sucking" style bypass (rather than true bypass), where the input jack is always connected to the effect, and the output jack is switched between the effect out and the input jack.  The other pole on the switch turns the LED on and off.  So the bypass will work even if the entire pedal isn't getting power.  My hunch is something coincidentally got damaged taking the board out, or while doing the mod, that maybe has nothing to do with the mod.  There isn't any effect coming through AND the LED doesn't work, the only things those two circuits share is the same power and the same stomp switch (and they share a ground connection too).  1st thing to do is to pop the back off and check with a voltmeter at the power jack and see if the effect is getting power at all.

Did you change the color of the LED?
I have done some lab practices where I use a LED to indicate something. For some reason, one time when I changed a red LED for a Blue LED the circuit didn't seem to work. My assumption was that since blue LEDs have a higher voltage (about 3V vs a 1.5 red one) there is a voltage fall that affects your circuit.

It takes > 3 volts to turn a blue LED on (ever noticed with keychain flashlights the red LED ones have a 1.5v battery in them, the blue and white ones have two 1.5v cells stacked on each other, or a 3v lithium battery), but the 9v the phase 100 is feeding it should be plenty.