It's not so simple to get access to the chassis and the main tuning condensor. On both of my sets, the tuning mechanism of the shortwave bands didn't move because of the gears of the tuning condensor needed cleaning.

to get access to the chassis

• loosen the four screws on the rear of the set, pull the back cover downwards and lift it off pulling it downwards - backwards (make sure not to tear off the prominent plastic holders at the top).
• Lift off the frontcover at it's lower part and flip it off very carefully, make sure not to break the tiny plastic holders on the front side, too.
  
• Set all dial pointers to the middle position. Unlock the front dial by carefully pressing with Your thumbs from the bottom to the top, flip the dial slightly out at the bottom until it gets loose. Pull it out of the pointer holder and carefully remove the front dial.
  
• You can loosen all knobs at the sides of the receiver and remove them to the outside. You can remove the telescopic antenna from the holding clip and remove it by pulling it backwards / downwards.
  
• After removal of two screws underneath, where You have taken off the front dial and two more screws below the dial at the left and at the right, You will be ready to lift the chassis out of the cabinet.
• You can also pull out the dial pointing to the top of the set by pulling it, unlock the pointer holding mechanism and carefully slide out the AM/FM dial.