Connex Mods:

3300 (early) Frequency Expansion:

1. Remove the top cover from the unit and locate the row of 15 pins across the front of the unit. Unsolder the short jumper wire from the 7th. pin to pins 11 and 12 (connected together). 
2. Unsolder the shorting solder bridge of pins 11 and 12 so that they are independent pins having no connection between them. 
   

3300 (late) Frequency Expansion:

1. Remove the top cover from the unit and locate the resistors on the bottom of the main PCB.
2. Unsolder them and remove them THAT'S it.

4400 Frequency Expansion:

Done.