After rebuilding the PCBs, the final step of the restoration of the electronics of a Beogram 4004 (5526) is replacing the incandescent light bulbs in the RPM trimmer panel with LEDs. This reduces the heat load on the RPM trimmers, which improves their stability over time. This is recommended since thermal changes can affect the RPM stability of the platter motor. Here is a photo of the panel taken out:
After removal of the two covers the bulbs can be accessed:
This shows the bulbs replaced with the LED based assemblies:
They are direct drop in replacements with the proper resistors installed to make the LEDs compatible to the 24V that are used to drive the bulbs:
The covers install exactly like before:
And this shows the 33 RPM LEDs in action:
They achieve a warm incandescent glow due to mixing red and green LED light in the right proportions to yield a color temperature similar to an incandescent bulb, while ensuring that red light is present to properly illuminate the red indicator.
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