Beogram 4000: Restoration of the Keypad Assembly - Gold Plated Switch Terminals and Light Bulbs Replaced with LEDs

After restoring the arm lowering and tracking mechanisms, it was time to rebuild the command center of this Beogram 4000. The keypad assembly contains an early digital control system, which responds to inputs by the keys on the keypad. The mechanical switches associated with the keys are one of the most often malfunctioning features of this design. This is why we recommend to gold plate the terminals in these switches to ensure trouble-free long term performance after the restoration process.

This shows the keypad cluster extracted from the Beogram and opened up:

One immediately sees that one of the light bulbs of the position indicator scale is missing. The other, still present one was not working, too. The chips that are visible are early TTL gates that comprise the digital control system that orchestrates the functions of the Beogram. The keypad switches are located in the lower PCB:

The black spots are oxidation, which often renders these switches permanently open circuit. A quick fix is to pull some 2000 grit sand paper through the terminals and their counter electrodes. But this is only temporary since the oxidation quickly grows back. It is better to remove the terminals, clean them and then electroplate them with a layer of gold. This shows the terminals removed in their original condition:

And after the plating process:

After soldering them back in the OFF button started to work again. After restoring the switches I replaced the light bulbs with LEDs. For the position scale illumination I use red/green LED-based assemblies that are tuned to emit an incandescent-looking spectrum which contains also red. This is important since the position indicator is a red piece of plastic, which would not appear red without the presence of red photons in the LED light. This is the reason I do not use amber LEDs for such tasks. The position indicator would look grayish in the light of amber LEDs. This shows the LED boards:

The RPM indicator bulbs can be replaced with standard red LEDs and current limiting resistors (the bulbs run on 12 V):

This shows the LEDs installed and in action:

And this is how the LED keypad illumination appears when looking at the keypad:

Beolovely! On to the carriage position indicator switches (you guessed it! they also need to be gold plated...;-)!