Replacing the incandescent light bulbs

I’ve been working on a small, plug-and-play replacement for the original incandescent bulbs used in the RPM adjustment section of the Beogram 4000 keypad. Since those bulbs usually burn out after 40+ years, the goal was to create something durable and easy to install, while still keeping the look and feel as close to the original as possible.

My first idea was to use a warm-white through-hole LED with a 1W resistor, but that setup turned out to be too bulky. The light also didn’t quite match the warm spectrum of the old bulb. So I moved on to designing a custom PCB using two red-green SMD LEDs. By adjusting the resistor values for each colour, I was able to get the light much closer to that original warm tone. Using two LEDs also helped boost the brightness to a level that worked in the context of the Beogram.

I tried out a few different PCB layouts and ended up going with a small square version. It allowed the LEDs to sit close enough to the aluminum housing, which was important for the overall effect. After that, I designed a 3D-printed housing to hold everything in place. It needed to be compact, easy to install, and not interfere with the nearby wiring. A few iterations later—thinner walls, better notches, some heat shrink for safety—I had a version that snapped into place and stayed there.



Update – Feb 2021:
I refined the housing design for a more secure fit. It now locks in behind the potentiometer housing (like the original bulb did) and is much less prone to breaking.

Update – Oct 2022:
I made another revision with a smaller PCB and found a warm-white LED that gets even closer to the original spectrum.

Update - Nov 2025:

An updated version is now available, designed to solder directly to the original points for even easier installation. See more here.

Feel free to reach out if you're curious or want to try it out.

Related PCB

RPM Adjusment Bulb Replacement PCB