Kenwood TM-x42 tri-band mobile radios have six 6.3 volt incandescent bulbs arranged in three pairs of two bulbs each to light up the display. Eventually the bulbs burn out and since they’re wired in series, they go out in pairs.
I recently replaced the backlight bulbs in a friends TM-642 with white LEDs. I used what I had on hand, instead of trying to find diffused LEDs made for this purpose. In order to handle the different voltage and current requirements, the tiny SMT drop resistors had to be replaced as well. I used 330 ohm 1206 SMT resistors to replace the 3.3 ohm 0603 SMT resistors.
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