Quote:
Originally Posted by Spunbearing
That is a good point. Does anyone know the layout of these boards better or know how the brake/marker light dimming is controlled? I am going to have to do more work to isolate the circuit.
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Full disclosure - I don't
know how this circuit works - this is guess work.
But, given that the IC driving the lamps doesn't have a heat sink or look to be able to dissipate much excess heat, any dimming of the lamp circuit must be via PWM (yes, same PWM as the control of the aux. fan - although used in a different way in this case). The noise you hear when it's faulty supports this theory. I'm guessing the LCM varies the mark/space ratio of a square wave going to the tail lamp to modulate the brightness. The PWM used for lamp dimming is usually in the 1-2kHz range, right smack in the middle of our hearing range. When your tail lamp assembly is faulting (short or similar to ground etc.) the IC is delivering a high current at 1-2kHz and you can hear this, via the protesting components.
I should drag my oscilloscope out into the car park and check the tail lamp circuit- this would confirm the PWM operation. But it's cold and dark outside!
This fault just HAS to be an intermittent fault path to ground in the lamp assembly somewhere...