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Odd means of lighting an LED in YBA Integre DT.

142.31.64.141

h_h

I recently converted my aging YBA Integre DT's volume control to a remote Alps kit purchased off of eBay for the reasonable price of about $40 and am very happy with the results, but in the process, I spent way too much time puzzling over the power LED circuit. That sounds ridiculous until you know how it's powered.

The power switch is a DPDT that disconnects both legs of the power from the IEC C14 connector. When the switch is off, the LED is shorted by the "unused" throw of the DPDT switch.

When the switch is on, the LED has no complete circuit, but it lights! Voltage measurements with a Fluke DVM gave 37 VAC or 30 VDC across the LED when it was lit. I've searched this forum and googled it, and I've found no reference to this weirdness.

I'll leave the answer as an exercise for now.

Follow Ups:

RE: Odd means of lighting an LED in YBA Integre DT. - Nagratech 08:17:57 01/26/11 (3)
Two words: French Engineering

Those boys do it differently
- RE: Odd means of lighting an LED in YBA Integre DT. - h_h 11:27:17 01/27/11 (2)
  They sure do, but I do like the way they sound (or don't sound, however you want to articulate it.)
  
  The answer is:
  
  The LED lights due to the stray capacitance in the switch that transfers enough of the 60 Hz 120 VAC to the LED's wires to light it. If they didn't short the LED when the switch was off, it would be on all the time. The high voltage readings are still a bit of a mystery to me, but the high input impedance of the DVM can lead to strange behaviour, and "ghost voltage readings" that would disappear if any substantial load were present. It would be interesting to view it on a scope, but I didn't bother.
  - RE: Odd means of lighting an LED in YBA Integre DT. - Michel 20:48:16 02/03/11 (1)
    Hello h h,
    
    There is nothing magical about the way the power LED lights in a YBA Integre. If you have a closer look, you will see that there is a 100k resistor hidden between the body of the power switch and the front. It should be in a black tubing making it harder to see. This resistor is soldered to both sides of the switch.
    
    Regards,
    - Thanks, I didn't see it, but I'll look again. - h_h 10:22:57 02/04/11 (0)
      Is there no blocking diode somewhere with a better PIV than a LED to deal with the reverse swing? I wouldn't expect a LED to survive 120V reverse voltage.

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