01 Identifying Diodes and Zener Diodes
Sometimes it's difficult to distinguish between rectifier diodes and Zener diodes on glass-coated diodes. Generally, the black line indicating the negative polarity indicates a Zener diode, while other colors indicate a rectifier diode. A typical rectifier diode has infinite reverse resistance and around 5KΩ forward resistance. A Zener diode, on the other hand, has infinite reverse resistance and around 10KΩ forward resistance.
02 Zener diode's voltage regulation value
Without convenient instruments, the voltage regulation value of a Zener diode can be measured using the diagram below, but only within 30V. Adjust the power supply from 0-30V; the value at which further adjustment stops increasing is the regulated voltage. Measure the voltage across the two ends of the Zener diode.
03 Measuring small capacitance
Small capacitors below 0.01uF are generally undetectable with a multimeter. It is easy to detect a short circuit, but it is difficult to detect whether there is an open circuit (except for those with a capacitance meter).
The diagram below shows how a multimeter, when used with a pointer, can easily measure small capacitors of tens of pF or larger. The diagram depicts an amplifier circuit with a composite transistor. Using a multimeter, you can observe the pointer's movement to determine the capacitor's quality, but it won't measure the capacitance. You need to use the multimeter's 10K range for this purpose.
04 Resistor Fault
Resistor failures are generally due to open circuits and value changes. Most resistors are either open circuits or have value changes. Short circuits are less common, unless caused by carbonization. Value changes are usually not noticeable. When measuring in-circuit, for example, with a 50K resistor, you should measure it in both forward and reverse directions. If the first measurement is 50K and the second is 40K, it doesn't necessarily mean it's faulty, because of the in-circuit effect! However, if the first measurement is close to the value and the second is 100K, you should desolder it and test it again. This is because in-circuit measurements should not exceed the resistor's true value. For reference.
05 Transistor Measurement
We know that transistors come in NPN and PNP types. Generally, the base conducts forward through both the emitter and collector, but the voltage at the emitter and collector should be infinite. Don't just focus on the continuity; you must also measure the resistance at the E and C terminals! Generally, if a multimeter shows resistance at the 10K range, the transistor is faulty. It might work in some situations, but will cause malfunctions in others! Sometimes, a transistor will be in a critical breakdown state, which is difficult to detect with a multimeter because a multimeter's battery only reaches a maximum of 15V. There was a TV with a clicking noise in the audio, which most people assumed was due to poor contact. I repaired one of these faults, and replacing one of the transistors in the audio output fixed the problem.
In the past, there were gold-encapsulated transistors like the 3DG6 and 3DG12. Their pin arrangement was: pins facing up, head down, notch facing itself, left for generator, right for collector, and center for base! Now, most are small plastic-encapsulated transistors. The pin arrangement of these small plastic-encapsulated transistors is not consistent; some have the base in the middle, and some have it on the side.
This requires us to use a multimeter to measure! If you find two pins that show infinite readings in both directions when measured with an analog multimeter, then these two pins are the emitter and collector. Next, connect the multimeter probes to these two pins. For an NPN transistor, lick the black probe and the empty pin (base) with your tongue, then switch the EC probes and lick again. The one with the larger pointer swing is the collector connected to the black probe. The measurement method for a PNP transistor is the same, except you lick the red probe instead.
06 In-circuit measurement of small axial flow fans
Some frequency converters are connected to the RT terminal. Sometimes, to determine if an axial fan is functioning, it's helpful to check if the resistance at the RT terminal is very low. The method is as follows: Connect a 10-ohm or 1K-ohm multimeter (analog multimeter) to the RT terminal, and manually rotate the fan blades of the axial fan. If the meter needle vibrates, it indicates that an axial fan is generating electricity! This means that an axial fan is connected to the RT terminal and is functioning properly.
07 Television Components Surface Acoustic Filter
Older televisions had a component called a surface acoustic wave (SAW) filter; I'm not sure if it still exists, as I haven't repaired televisions in a long time. If there's no picture or sound, but only static, you can solder a small 0.047uF capacitor to the input and output terminals of the SAW filter. At this point, both picture and sound should appear, because a multimeter cannot determine the condition of an SAW filter. Then you can remove the capacitor and replace it with a new SAW filter.
These are some accumulated experiences; everyone is welcome to share and discuss them!
