As with other kinds of diodes, a Zener is an electronic component that conducts electrical current in only one direction. Unlike other diodes, Zeners serve as voltage regulators, maintaining a constant voltage across its terminals when used in the reverse direction. The diode blocks the reverse current flow and holds the voltage between the anode and cathode steady over a wide range of circuit voltages. Like any electronic part, it can fail from excessive voltage and current. Fortunately, Zeners are common parts and simple to replace if you have basic electronics repair skills.
Locate the Zener diode on the circuit schematic. Write down its part number, if available, and its voltage.
Find the Zener part number in the diode section of the electronics distributor catalogue. Obtain the part.
Unplug the electronic equipment from the wall outlet. Open the case.
Examine the circuit board and find the Zener diode. Note that it has a stripe on the body of the part indicating the diode's cathode lead. Sketch the Zener's location in the circuit relative to other parts, showing the orientation of its band.
Locate the two solder pads on the bottom of the circuit board.
Touch the hot tip of the soldering iron to one solder pad just long enough to melt the solder. Draw the liquid solder off with the desoldering tool. Repeat for the other solder pad.
Remove the old Zener diode by grasping it gently with the long-nose pliers and working it loose.
Bend the leads of the replacement Zener diode 90 degrees relative to the body so they both point down. Orient the diode so the stripe points in the same direction as the original did, referring to your sketch for the correct placement. Insert the diode into the two holes in the board.
Solder the new diode to the solder pads. Clip excess lead material flush to the pads with the diagonal cutters.
If you cannot locate the Zener's part number, use its voltage and watt ratings to find a substitute in the electronics distributor catalogue. Parts manufacturers produce Zeners in a range of voltages from a few volts to about 200 volts.