LED will not work

[jschwalls]

i have a BOSS PH-2 and the LED doesnt work... i tried swapping with a new one but that doesnt work either.. the pedal works fine otherwise.

whats up ?

JON

[GibsonGM]

You'd need to engage the effect, and measure the voltage from the point the + lead of the LED attaches to, to ground (battery - terminal).   Report that voltage here, and also measure the current at the same point.

If both measurements = 0, follow the ckt backwards until you find the current limiting resistor that goes to the LED (usually from 2k or so, down as low as 300 ohms).   It may be burned out.   With no power, LED can't light up!   If it's dead, change it...but there may be a problem before that resistor that led to it burning out....

[jschwalls]

ok the DCV was 1.2

that reading was at the LED and at both sides of resistor.. BUT it was 6.3V before the diode which leads to the resistor... maybe the diode is bad ??

the resistor is new, so the lowering of voltage must be the diode..

right ?

[GibsonGM]

Bingo.   What kind of diode?  Is it a little guy, like a 1N914?  Could have to do with polarity protection...someone might have put power to it backwards.     Test the diode with an ohmmeter.  You should get 100's of Kohms in one direction and Mohms in the other.  No reading = blown.   You can just replace it anyway, regardless; write down which side the cathode (band) is on so there's no error doing it.  And replace the LED - watch the polarity of the LED, too.
Then it should work, if there's nothing else going on )

[oskar]

I didn't find a schemo for this one, but another Boss I saw had a ~6v something zener with the LED/resistor.
The chain was:
       V+  , LED , Resistor , zener , flip-flop (transistor pulls to ground)