Following the replacement of the reservoir and motor capacitors in the Beogram 4000, I focused on upgrading the control panel’s light bulbs. LEDs offer greater long-term stability and are generally preferable replacements for incandescent bulbs, except in cases where the original circuitry or aesthetics demand otherwise. Given that the control panel’s lighting is internal and not directly visible, LEDs are a suitable replacement. In this instance, one of the bulbs illuminating the position scale had failed, causing the entire scale to go dark due to the series arrangement of the two bulbs.

To address this, I created a small circuit board to house two red/green SMD LEDs and their corresponding current-limiting resistors. This combination effectively replicates the appearance of incandescent light. I opted for red/green LEDs, rather than the more common amber LEDs, for their ability to illuminate the scale’s red indicators, which lack of red photons in amber LEDs would not properly illuminate.

The two bulbs originally used to backlight the RPM trimmers were replaced with standard high-brightness red LEDs and suitable current-limiting resistors.

For a visual guide to the entire process, from opening the control panel to installing the LEDs, a brief video is available.

Here are some photos from the video:

These are the red/green LED assemblies for illuminating the scale (using Newark 75R0619 LEDs with 1.25kΩ resistors for red and 6kΩ for green):

The RPM trimmers were replaced with these (using Newark 08R2974 LEDs and 3.3kΩ resistors - the photo shows 1kΩ resistors, which were excessively bright):

This image shows the installed LED assemblies:

And here they are illuminated:

This image showcases the operational control panel with the newly installed LEDs. The result is a rather authentic look. We opted for brighter RPM trimmers than the original, ensuring visibility in a lit room. The original dimness made them nearly impossible to see without turning off the lights. Of course, this can be adjusted using larger resistors. To achieve an identical look to the original’s low brightness, low-output LEDs (Newark 14N9416) and 220Ω resistors can be employed: