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guycom 28th September 2008 09:04 PM

Brian gt chip amp power supply?
Hi, Looking for some help. Power supply is done using a centertap 3wire output transformer with help from the picture with diod reconfig. I am getting 17.8 volts output unloaded with no light from the led. Pulled and rotated led to change polarity no light. As always thanks for you help,

wakibaki 28th September 2008 09:27 PM

LED is dead if you have voltage at its pins and no light either way.


guycom 28th September 2008 09:32 PM

I understand. Are there different values for leds?
Thanks Again,

guycom 28th September 2008 09:35 PM

I am reading .3 volts dc at the led.

wakibaki 29th September 2008 09:57 PM

The LED is probably dead short-circuit.

LEDs run RED ~1.2 -> 3.6V BLUE depending on colour and how hard driven.

Take the LED out of circuit. Measure the voltage at the pads. You should see the full supply voltage or at least a substantial voltage depending on the exact circuit. If this is the case the LED is definitely dead, if not you have an open circuit somewhere.

A small lithium button cell is good for quick testing LEDs without a resistor. They can drive even a blue LED, but cannot deliver enough current to destroy.


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