Beogram 4000: Restoring the Carriage Position and Solenoid Driven Switches

After rebuilding the keypad cluster of this Beogram 4000 it was time to see to the remaining mechanical switches that control the Beogram's performance. There are two clusters, one beneath the carriage where the switches determine the position of the tonearm, and the other next to the solenoid. The solenoid activated switches are responsible for the activating the tracking mechanism, opening the outputs when the needle is in the groove and to regulate the solenoid power down once the arm is lowered.

This shows the carriage position switches. For getting to them it is best to drive the carriage inwards and remove the red position indicator assembly. Then the board is fully accessible:

After unsoldering the two leads that power the carriage motor and removal of two screws the board can be pulled up and turned around:

Some oxidation is visible on the back of the terminal tabs. For some reason the carriage position switch terminals are usually less oxidized than the other switches under the keypad and next to the solenoid. I removed the terminals

and coated them with gold:

Then it was time to solder them back in and clean the plastic plungers that activate the switches from 40 year old hardened grease. Then I turned my attention to the switches next to the solenoid. The single switch assembly that controls the solenoid power can be directly accessed after removing the two screws that hold it in place:

I extracted the terminal and then removed the assembly that holds the output and tracking activation switches:

This assembly needs to be taken apart while not ripping the thin wires off that are connecting the switches to the control system:

Once this was done I extracted the three terminals. This shows all four terminals as extracted:

'Beautifully' oxidized, I'd say! I brushed the oxide off with 2000 grit paper and a fiber glass brush and then coated them with gold:

That looked much better! I put everything back together and gave the system a first test...Good news: so far everything seems to work...the carriage is now setting down the arm at the 12 inch point and the solenoid actuated properly. A significant milestone has been reached in this restoration!

Beogram 4000: Gold Coating of Solenoid Activated Switch Terminals

The third group of switches that control the Beogram 4000 is comprised of four switches that are activated by the solenoid when the tone arm is lowered. Like the other switches in keypad and under the carriage these usually suffer from oxidation. One of the switches is particularly important, since it controls the solenoid current during lowering activation. If it is oxidized, the arm will not lower anymore. Therefore, we strongly recommend to also get these switches gold plated like the others. This shows the switch assembly next to the solenoid (this photo shows already the gold plated terminals - I forgot to take a picture of the original condition):

The switches are installed on the three small vertical PCBs that are soldered to horizontal base-PCBs. The left most switch activates the tracking system once the arm is down. The two switches on the center PCB are the output switches that ground the cartridge signal lines while the arm is up, and the right most switch (under the wide yellow conduit) reduces the solenoid current to a lower value once the arm has been lowered.

These switches are a bit more difficult to get to than the others since they are connected to many flimsy wires. The solenoid current switch terminal is the only one that can be removed directly after unbolting its base-PCB:

The other two vertical PCBs need to be removed from their base-PCB to access the switch terminals. The first step is to unbolt the base-PCB and turn the board around that the solder points for the vertical boards can be accessed:

Unsoldering requires three hands, but with a de-solder pump and a bit of persistence it can be done with only two...;-):

After removing the oxidized and deformed terminals

I electroplated them:

And then it was time to put them back in:

Nice! On to the PCBs!