HOW TO RECAP A ROYAL 500-D RADIO
DISCLAIMER: The information provided here represents a number of tips that I use in recapping a Zenith Royal 500 radio. These 50 year-old radios are very fragile and easily damaged, especially by users inexperienced in electronic repairs. Use this information at your own risk, with the understanding that I am not responsible for any unsatisfactory outcomes.
Recapping the Royal 500 can solve many poor performance problems. There are 4 electrolytic capacitors involved. The good news is the price of these parts is around one dollar. They are available from Jameco, Digi-Key, Mouser and many other electronic stores. The two 50 mfd capacitors can be replaced with units having the modern-day value of 47 mfd; the 3 mfd units can be replaced with either modern-day 3.3 mfd or 4.7 mfd. The earlier 7 transistor Royal 500 chassis uses a 16 mfd in the AVC position; this can be replaced using the 16 mfd or a 22 mfd value. (Also, it is located in a different location than the Royal 500D pictured in these illustrations.) Electrolytic capacitors are polarized with a positive and negative lead. The replacement capacitors have to be installed with the correct polarity or your radio will not work correctly.
Begin by placing your radio on a towel or other scratch-free surface. The volume knob is a one-piece unit; however, the tuning knob has both an inner and outer knob. Begin tuning knob removal by applying equal pressure on both sides of the INNER knob first. It will pop off. Next, apply gentle equal pressure of the outside knob. Repeat the equal pressure procedure for the volume control knob. Don't pry from one side onlyyou will be guaranteed a broken knob!! Also, if the knobs are stubborn, keep up the gentle-even prying pressure; they will come off eventually. PATIENCE!!! Also, NEVER try removing knob by prying with a screwdriver; you will end up with a marred case and a broken knob!
|Once the knobs have been removed, remove the 2 screws from the rear cabinet. This will permit removal of the cabinet rear.|
the rear cabinet removed, the chassis can be unfastened by removing the retaining
post by the main tuning capacitor and the 2 Phillips screws located at either
side of the battery box. Carefully, remove the chassis from the front cabinet
section. Here a shot of an "inverted cone" style speaker.|
|If your radio has the inverted cone speaker, do not let radio rest on the cone during this next step. Remove the speaker retaining screw (some models have 2 of these). Carefully remove the speaker from its nesting place in the battery box.|
|Next unsolder the speaker and remove to a safe location. If you leave it nearby, you run a risk of punching a hole in the speaker. While these speakers still play well, the speaker cone is extremely fragile and easily damaged. Also, remove the cabinet and battery cover to a safe location away from your work area to avoid accidentally scarring them with your soldering pencil. Next, gently pull away the paper tapes holding down the three rear electrolytic capacitors. They can be reused.|
Capacitor area before tape removal.
Tapes lifted to expose capacitors.
|Here is a shot of the AVC, Battery decoupling, and audio driver transistor emitter bypass capacitors that will need replacing.|
|Here is a shot of the audio coupling capacitor which connects from the center terminal of the volume control to the PC board.|
|To the right and the bottom are shots of the earphone jack. The bottom earphone jack connection is used as common tie point for the 2 electrolytic capacitors, a thin wire from the output transformer, and another wire that goes to the main PC. I use a solder-pump to remove solder. I find that this is the most "dicey" part of the operationremoving the two old capacitor leads and installing the new ones without causing any damage.|
|Work carefully in this area to avoid damaging the earphone jack or wiring.|
|After replacing the 4 electrolytic capacitors, carefully inspect your work to make sure that the capacitors are installed with the correct polarity. Also, make sure that you have not created any wiring shorts. Reinstall the speaker. Finally, check your radios performance before reinstalling it in the cabinet.|