Beogram 4000: Restoration of the Keypad

After restoring the arm carriage components of the Beogram 4000 that I am rebuilding right now, it was time to do the keypad. The keypad is the command center of the turntable and contains the TTL logic components of its 'early stage' digital control system. The keypad needs to be removed before one can get to its components. A single screw holds it in place:

The remarkable feature of this particular keypad was that there were no wires visible underneath it. All the other 4000 had the keypad wiring folded directly behind the latch that is bolted down. When I pulled this keypad up I found this arrangement:

An interesting way to do it, letting the wire harness enter the pad from the front. And much less painful to arrange when putting the pad back into its bay. This is how the harness exits the keypad in this arrangement:

Anyway, I thought I go on the record with this finding...You may think Beolover = Beonerd, I could not possibly comment...;-). On to the restoration:

This shows the keypad extracted:

and in 'service position':

The first item to take care is to replace the often frail light bulbs that illuminate the arm position scale and the RPM trimmers. This is the original arrangement:

I replaced the scale bulbs with my red/green LED based assemblies

Like all Beolover parts shown on the blog, they are available to other enthusiasts. Just send an email or use the contact form to the right if you are interested. The RPM trimmer illumination bulbs can be replaced by regular red LEDs and appropriate resistors to limit the current (they run at 12V...):

This shows the LEDs installed:

And 'in action':

The next step was to clean the switch terminals that were oxidized as usual. I pulled 2000 grit sand paper strips through the switches while actuating them. This cleaned the contact area from oxide. Subsequently, I coated them with a bit of DeoxIT D100 to slow down re-oxidation. One of the switches, which is under the 'down' key, needs special attention since it is hard to reach under the keypad hinge. It is best to extract it that the oxide can be cleaned off properly in the contact area. This is how it looked as extracted:

and after gently sanding it:

After I reinstalled the terminal, I checked all switches for proper contact resistance with a multimeter and then I put the pad back together. This is how the LEDs appear from the top of the pad:

Please, note that the position indicator was not installed when I took this picture. This concludes my work on the keypad. On to the electronics and the motor.