Your assumptions are in order. '''A trickle charge is sent from the power supply to the first LED. If the first LED is not lit the power supply is not working.''' I would suspect a possible bad connection except a trickle charge doesn't carry much current or voltage. - Just enough to supply the LED.
The diagnostic LEDs to the right of the RAM slots (this may be covered by a piece of black electrical tape). - you noticed that.
LED Startup Sequence
LED #1 = Power available.
If no LED is visible:
• Verify AC source
• Verify known-good AC cable is connected
• Verify cable connection between AC inlet and power supply
• Verify cable connection between power supply and logic board
• Verify power supply
LED #1 + LED #2 = Power available, and system is powered on.
If second LED is not visible when power button is pressed:
• Verify power button connection to logic board
• Verify power button functionality
• Verify cable connection between power supply and logic board
• Verify power supply
• Verify logic board
LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found.
If third LED is not visible after power on:
• Verify that MXM video card is seated properly
• Verify logic board
If no lights are coming on you need to replace your power supply. A trickle charge is sent from the power supply to the first LED. If the first LED is not lit the power supply is not working.