If you need to replace a fuse in a television, the first question to be asked is why the fuse blew in the first place. It could be caused by a faulty component, a shorted power supply, a broken vacuum tube or the fuse could even be defective. Regardless of the cause, fuses respond to excess current flow and cause the circuit to open. This eliminates the possibility of additional damage from the high current. Television sets use various sizes and types of fuses.
Depending on the age and technology of your television, you can expect to see a wide variety of fuses and fuse types. The fuse type is determined by the circuitry it is protecting. The main characteristics of a fuse are its construction, voltage rating and current rating. Certain applications dictate construction. For example, the ability to withstand moisture is critical in a marine fuse. The voltage rating specifies the maximum voltage the fuse should be exposed to, while the current rating is the current required to cause the fuse to open.
Glass or Ceramic Fuses
The tubular glass, or ceramic fuse, is glass is the most commonly used fuse in television sets. The glass fuse has a current-conducting strip or wire of fusible metal. The strip melts, and the circuit opens, when the circuit carries a current higher than its rating. One of the advantages of the glass fuse is the ability to see the fusible wire. Glass or ceramic fuses are general purpose fuses.
A fusible resistor serves as a resistor until the current level reaches the rated value. At its rated value, the resistor opens, protecting the circuit against damage. In normal operation, the fusible resistor acts as a resistor, limiting the current available to the circuit. In older CRT televisions, fusible resistors are usually found in the power supply circuitry.
Pico fuses look like small resistors. Their design makes them ideal for mounting directly on printed circuit boards. Pico fuses take up less space than other types of fuses. This makes them an obvious choice on newer television systems. Pico fuses lend themselves to automated production since they can be machine installed on printed circuit boards. Since the Pico fuse is soldered on a printed circuit board, it is more difficult to test. Pico fuses are typically marked F or PR on a printed circuit board. PICO is a registered trademark of Littelfuse.