Old capacitors in an must be removed and replaced with like-size and type.
Capacitors are used to smooth out signals and voltages in electronics, especially radios and televisions. Capacitors pose a problem in older antique radios because they have components within them that degrade over time. When reconditioning an antique radio to make it operational, you may need to remove an old capacitor and replace it with a new one of the same size. Capacitors are rated and measured in farads, microfarads or picofarads. These ratings are printed on the exterior of each capacitor. Ceramic capacitors are flat disks, while electrolytic capacitors are round vertical cylinders. Electrolytic capacitors with polarity (positive and negative sides) must be installed in the proper direction on the board.
Instructions
1. Remove the exterior cabinet or casing from the radio by removing all screws with a Phillips-head or flat-head screwdriver. Lift or pull the exterior away from the interior metal chassis to reveal the circuit board.
2. Remove all screws that secure the circuit board to the risers in the radio chassis so that the board can be tilted or rotated as necessary when preparing to desolder old capacitors and to solder in the new ones. Keep the circuit board mounting screws in a separate location to help in easing reassembly.
3. Plug in the soldering iron and wait 10 minutes for it to come to maximum operating temperature. If the soldering iron has an adjustable temperature switch, set it between 25 and 35 watts, with 25 watts preferred.
4. Draw out a rough sketch of the circuit board and how components are laid out on that board. Draw this out on a blank piece of typing paper. Draw a circle in the locations where capacitors are located and write down the type and farad values inside of those circles. Ceramic and mica capacitors are round disks or flat rectangular-shaped devices, whereas electrolytic capacitors are vertical cylinders with a (+) printed near one wire leg and a (-) on the other wire leg.
5. Mark all positive (+) sides of the electrolytic capacitors on the board. If a capacitor is electrolytic, place a small red dot on the where the positive (+) wire of the capacitor pushes through the board.
6. Unroll a 4-inch piece of desoldering braid from the spool and use wire cutters to cut the length from the spool. Put on a pair of thin leather gloves to protect fingers and hands from any hot solder splatters and from hot desoldering braid.
7. Rotate the circuit board to expose the underside. Touch the desoldering braid across the two solder beads holding the capacitor in place, and then press it down with the hot tip of the soldering iron. The heat will distribute across the braid causing the solder to melt, as the old solder will be absorbed by the braid. Once the old solder has been absorbed, use a pair of needle-nosed pliers to pull the capacitor away from the board. Don't use fingers, as the capacitor may be hot to the touch. Use a new piece of desoldering braid when desoldering each capacitor.
8. Slide the wire legs of the new capacitor through the holes in the board where it is to be installed. For non-electrolytic capacitors, it doesn't matter which leg goes through which hole. For electrolytic capacitors, look for the red dot placed on the board and slide the positive (+) wire leg through that marked hole. Press the capacitor downward onto the board until the bottom of the capacitor touches the board.
9. Hold the new capacitor on the board and reach around to the bottom where the wire legs are protruding through the board. Gently bend the wires outward slightly to prevent the new capacitor from falling off the board while soldering.
10. Touch the tip of the soldering iron to one of the legs on the new capacitor, making sure the tip of the soldering iron touches the leg and the metal pad on the underside of the board so both are heated. Allow the tip to heat the leg and the pad for about 5 seconds, then touch the tip of the solder to where the leg is in the hole. Allow just a small bead of solder to melt onto both the wire and the circuit board pad, then remove immediately. Apply a bead of solder to the other leg in the same way.
11. Desolder and install only one new capacitor at a time until all have been replaced, making sure the capacitors are all replaced with the same type and size as the ones being replaced.
Tags: circuit board, soldering iron, desoldering braid, , antique radios, away from