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Blaupunkt display backlight

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Discussion in 'Troubleshooting and Repair' started by zhv, Mar 27, 2013.

  1. Mar 27, 2013 #1
    zhv

    zhv

    8
    0
    Jan 7, 2012
    I am in the middle of repairing a Blaupunkt Montreux RCR44 radio. One of the problems is that display backlight does not work. I found that the replacement bulb (who knows when it was changed) was incorrectly soldered to the board. During desoldering I accidentaly pulled one of the wires off the bulb with no way to solder it back. At that time I thought what if I could replace the bulb with a LED. Since I want to make this radio look as original as possible, I want the backlight LED to match the color of the button backlight. After searching the schematics I found that the LEDs behind the buttons are LY3880GK type (supposed to be yellow, but it looks more like amber). However the bulbs work on 14V and draw about 100mA (according to the schematic). What options do I have to replace the bulb with a LED?

    Link to schematic
     
  2. Mar 27, 2013 #2
    CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    Replace bulb with a warm white LED, and a 680 Ohm resistor (1/2 watt or greater) in series and you should be fine...

    The warm white LEDs are a very similar amber color to incandescent bulbs, vs the blue/white of normal 'white' LEDs...

    I recommend the 'straw hat' profile LEDs as they through light much less directional more like a bulb...
     
  3. Mar 27, 2013 #3
    zhv

    zhv

    8
    0
    Jan 7, 2012
    Gah! I didn't even think about warm white LEDs. I also forgot to add that the bulb sits in a special rubber colour filter, which is supposed to give the correct color to the light and keep it in the correct place.

    The only warm white LEDs I can get my hands on are these: LINK
    I calculated that I would need 470Ohm and 1/2 Watt or greater resistor to keep it below maximum allowable current. It should cut down a little on the brightness.

    Would these work? I hate ordering stuff just to find out that I miscalculated something.

    Thanks, CocaCola!
     
    Last edited: Mar 27, 2013
  4. Mar 27, 2013 #4
    CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    Just put the LED in that filter, again straw hat LEDs throw light similar to bulbs, not a focused beam...

    I would get some straw hat ones on Ebay... 50 degrees isn't bad though and might look OK if you go that way, although if they are still too spot like you can buff the top with some sand paper...

    Are you sure a 5mm will fit? I actually did this exact same thing a few years back and found 3mm LEDs to be a better fit, I also tossed the red-ish filters as they were all dried up and rotten and just went with diffused red LEDs...

    For automotive applications use 14.5 - 15 volts in your calculations not 12, as that higher voltage is the average charge voltage of a running vehicle and fully charged battery... When you do this you will see why I chose 680 Ohms...
     
    Last edited: Mar 27, 2013
  5. Mar 27, 2013 #5
    zhv

    zhv

    8
    0
    Jan 7, 2012
    Well, eBay is no go. I do have a time limit on this one and I can't wait for shipping. I guess I could roughen the LEDs surface and use the color filter I already have (mine is in perfect condition, guess it was changed when the bulb was). Then it should look almost as good as a regular bulb.
     
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