#1
So I am a little new in the MOD world...
I successfully changed out two of my pedals to a nice blue LED...
When I got to my 3rd "MXR Dyna Comp"...the LED sizzled and burned up as soon as I turned it on...

Anyone know why this would be? I would assume since it was an LED change there would be a resistor onboard already?

The LED specs are :
forward (supply) 3.7 typ.
voltage: 4.5 max

Forward (supply) 20mA typ.
current: 30mA max

Luminous intensity 2600mcd

thanks for any help.
Joe
#2
It's getting too much juice. If you have a multimeter, you can measure the voltage going to the LED. When this is too high, you'll burn out the LED as described. The way to fix this is to add a resistor before the LED.

Use Ohms law to determine the value of the resistor you need.

I=V/R

Based on the values you gave, that's:

.02A=3.7v/R

R=3.7v/.02A

R=185 Ohms
Gear
  • 2004 Am. Strat
  • 2004 Mex. Tele
  • 2005 Esteve Classical

  • Vox Valvetronix AD15VT w/ foot switch

  • Vox 847
  • EH Stereo Polychorus
  • Ibanez TS-808
  • EH Big Muff Germanium 4
  • EH Small Clone
  • EH Small Stone (USA Ver 2)
  • EH LPB-1
  • PlusEBow
#3
I think one possible cause may have been:......

I was not sure which lead was positive so I was just testing if the LED was working...the MXR has metal screw on input/output connections so I had to put the pedal back together to test...
I had not insulated the leads yet so maybe they were too close..
#4
Quote by ns9977a
It's getting too much juice. If you have a multimeter, you can measure the voltage going to the LED. When this is too high, you'll burn out the LED as described. The way to fix this is to add a resistor before the LED.

Use Ohms law to determine the value of the resistor you need.

I=V/R

Based on the values you gave, that's:

.02A=3.7v/R

R=3.7v/.02A

R=185 Ohms



so I guess your were right...
I connected a volt meter and the LED is getting 8.75 volts.
I guess mxr uses a high voltage LED?
#5
Assuming no other changes to the circuit it would have to. Like I said, it's an easy fix, just add the resistor.
Gear
  • 2004 Am. Strat
  • 2004 Mex. Tele
  • 2005 Esteve Classical

  • Vox Valvetronix AD15VT w/ foot switch

  • Vox 847
  • EH Stereo Polychorus
  • Ibanez TS-808
  • EH Big Muff Germanium 4
  • EH Small Clone
  • EH Small Stone (USA Ver 2)
  • EH LPB-1
  • PlusEBow
#6
Quote by ns9977a
Assuming no other changes to the circuit it would have to. Like I said, it's an easy fix, just add the resistor.



I learned the proper way to calculate what resistor I need...
my local radio shack was out of the blue so I gave the pink a try...looks pretty cool on the dyna comp.

I should have used a volt meter in the first place...I had no idea the MXR would send 8.75 v to the LED!