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Old 25th December 2013
  #103
Here for the gear
 

LeeYoo, your info here and elsewhere on the 828 backlight fix has been invaluable to me. Let me add a couple of details from my experience:

I thought I'd try replacing the (dead) green LED on my 828 mkII with a red LED. Picked up a 3 mm red LED from a local electronics shop and soldered it into the two holes marked 'A' and 'K' - the anode and the cathode for the LED. These are connected to the big solder blobs that the original backlight LED is connected to. The 3mm LED is a great fit - easy to position it so that it is pointing right into the slot where the original SMD LED was:




Put the 828 back together fired it up and.... nothing. Took it apart and tested the LED and it was dead. Measured the voltage going to the LED - it's 11.5V! (LeeYoo mentions this is a rail voltage on another forum). Vf of my red LED is about 1.8V whereas Vf of a green LED is somewhere around 3V, so perhaps the current limiting resistor on the main board is just enough for a green LED but not enough for a red LED. With a superbright green LED connected, I measured a Vf of 3.6V and a LED current of 42 mA! No wonder these LEDs are getting fried. The current limiting resistor on the main board is on the bottom side, as far as I can tell. I got the LCD/knob board out without removing the main board and wanted to leave it as is so I added a 330 ohm resistor in series with the anode. This gave a current of 17 mA for the red LED, 3 mA shy of its 20 mA rating. The resistor replaces the anode terminal to which one of the stray ribbon conductors connects. A little blob of solder on the resistor's terminal makes it thick enough to get a firm fit with the connector:



The result: