What is the smell of electrolytic capacitors on the motherboard when they are burned out, and what i

Electrolytic capacitors are used in large quantities in electrical equipment, and the failure rate is very high. Electrolytic capacitor damage has the following manifestations: first, the capacitance is completely lost or the capacitance becomes smaller; the second is minor or serious leakage; The third is the loss of capacity or the capacity becomes smaller, and there is leakage.

The ways to find damaged electrolytic capacitors are:

How it works: 1.Look: Some capacitors will leak when they are damaged, and there will be a layer of oil stains on the surface of the circuit board under the capacitor and even on the surface of the capacitor, and this kind of capacitor must not be used again; Some capacitors will bulge after being damaged, and this capacitor cannot be used anymore;

2.Touch: After booting, some electrolytic capacitors with serious leakage will heat up, and even hot hands when touching with fingers, and this capacitor must be replaced;

3.There is an electrolyte inside the electrolytic capacitor, and baking for a long time will dry out the electrolyte, resulting in a decrease in capacitance, so it is important to check the capacitor near the heat sink and high-power components, the closer it is, the greater the possibility of damage.

Detection method of electrolytic capacitance.

1.Because the capacitance of electrolytic capacitors is much larger than that of general fixed capacitors, it is necessary to select the appropriate range for different capacitances when measuring. Based on experience, stand.

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In general, the capacitance between 470nf and 10 f can be measured by r 1k stop; The capacitance of 10 F to 300 F can be measured in R 100 stops; Capacitances above 300 F can be measured in R 1 or R 10 stops.

2.When testing electrolytic capacitors, it is necessary to discharge the capacitor first, especially for large-capacity electrolytic capacitors, two pins can be directly short-circuited for discharge.

3.Then the red pen of the multimeter is connected to the negative pole, and the black pen is connected to the positive pole, at the moment of first contact, the multimeter pointer is deflected to the right by a large degree of skewness (for the same resistance, the larger the capacity, the greater the swing), and then gradually rotates to the left until it stops in a certain position. In this case, the resistance value is the forward leakage resistance of the electrolytic capacitor, which is slightly greater than the reverse leakage resistance.

4.Practical experience shows that the leakage resistance of electrolytic capacitors should generally be more than a few hundred K, otherwise, it will not work normally. In the test, if there is no charging phenomenon in the forward and reverse directions, that is, the watch hand does not move, it means that the capacity disappears or the internal circuit is broken; If the measured resistance value is small or zero, it means that the capacitor leakage is large or has been damaged by breakdown, and can no longer be used.

The electrolytic capacitor on the motherboard will burn up the electrolyte.

Runny or squirting, mushy smell.

Diode. And the transistor will break down, there is no smell, and even the surface does not change significantly.

In this case, it is likely to be caused by excessive filtration, and in the case of instant breakdown, it is necessary to replace a converter to control its power.

There is a big difference in the quality of mobile phone power adapters! If it is a high-quality original charger, it is not easy to damage! Most of the high-quality charging adapters use monolithic integrated circuits, with simple circuits, good stability and perfect protection measures, so that the charger will be automatically protected even if the output is short-circuited and will not be damaged.

It's hard to talk about the inferior ones: the charger gets water; Use it to charge other phones and overload; Charging multiple sets of batteries in a row causes overheating, and so on.

Name implies! The former is two-legged! The latter is three-legged!

An electronic vacuum diode consists of only a cathode (filament) and an anode! It only plays a single conductive role in the circuit!

Electronic vacuum diodes have a gate between the anode and cathode! It's a triode! The gate controls the current change between the cathode and anode! There is a amplification circuit for the current or voltage of the transistor!

A semiconductor crystal diode is a single-junction (p-junction) transistor composed of two monocrystalline silicon wafers or germanium wafers (n-type or p-type) with different doping characteristics! Under the action of the electric field applied by the two poles, the hole in the junction is dispersed and changes to form a unidirectional conductive characteristic!

Semiconductor transistors are derived from diodes! Generate two PN knots of different sizes and thicknesses on one substrate!

In this way, the current between the two junctions will be controlled by the potential of the substrate! This has the same amplification characteristics as vacuum transistors!

Both diodes and scatter electrodes have unidirectional conductivity! It's the common ground! The transistor has an extra controllable pole! With the circuit, there is an amplification function! It's a different place!

Similarities:

1. They are all made of semiconductor materials, mainly silicon materials;

2. Both can be used as switching devices;

3. The basic structure is inseparable from the PN junction; are the main devices of integrated circuits;

4. The encapsulation materials are all post-epoxy resin;

5. Therefore, the manufacturing process and equipment, raw and auxiliary materials are basically the same, such as diffusion, lithography, evaporation, HF, hydrogen, nitrogen, and other special gases; Pure water is used.

Differences: 1 The former is a p-n junction of one, and the latter is a p-n junction of two;

2. When the former is used, the function is rectification, clamping, voltage stabilization, detection, etc., and the latter and other components form amplification, oscillation, logic and other analog circuits and digital circuits;

3. The manufacturing process is more complex;

4 The former is mostly two-legged and leads out axially, while the latter is generally three-legged and radially leads.

5. As an emergency, EB can be used as a regulator tube and BC can be used as a rectifier tube in the two PN junctions of the transistor. Diodes are no substitute for transistors in any way.

The role of the triode and the diode du:

1. Triode:

The magnification area is within an amplification element;

The three-pole capacitor in the digital circuit works in the saturation or cut-off state and plays a switching role.

The triode has a base B, collector C, emission E three poles, in the digital circuit the triode is generally used as a "switch", when doing the switch, the voltage of the "base B" is higher than the "emission stage E" on the conduction, we call it "VBE> conduction. On the contrary, "cut-off", the current can no longer pass through, which is "on" and "off", that is, "0" and "1".

The "saturation" and "amplification" effects are specific to analog circuits and are not found in computer digital circuits.

2. Diode:

The diode is unidirectionally conductive, i.e., forward conduction and reverse shut-off.

Forward voltage is applied at both ends of the diode, the diode is on, the forward voltage drop, and the switch is quite an on/off;

Reverse voltage is applied at both ends of the diode, the diode is cut off, its current is 0V, and the equivalent switch is disconnected;

This characteristic can be used to generate high and low levels in digital circuits, generally with "1" representing high levels and "0" representing "low levels".

Fast recovery diode (FRD) is a kind of semiconductor diode with good switching characteristics and short reverse recovery time, which is mainly used in switching power supplies, PWM pulse width modulators, frequency converters and other electronic circuits, as high-frequency rectifier diodes, freewheeling diodes or damping diodes.

The internal structure of the fast recovery diode is different from that of ordinary PN junction diodes, which belongs to the PIN junction diode, that is, the base area is added between the P-type silicon material and the N-type silicon material to form a PIN silicon wafer. Because the base region is thin and the reverse recovery charge is small, the fast recovery diode has a short reverse recovery time, a low forward voltage drop, and a high reverse breakdown voltage (withstand voltage value).

The transistor is a kind of control element, mainly used to control the size of the current, taking the common emitter connection method as an example (the signal is input from the base, output from the collector, and the emitter is grounded), when the base voltage UB has a small change, the base current IB will also have a small change, controlled by the base current IB, the collector current IC will have a big change, the larger the base current IB, the larger the collector current IC, on the contrary, the smaller the base current, the smaller the collector current, That is, the base current controls the change of collector current. But the change in collector current is much greater than the change in base current, and this is the amplification effect of the transistor. The ratio of the change in IC to the change in IB is called the magnification of the transistor ( =δic δib, δ indicates the amount of change. The magnification of the transistor is generally in the tens to hundreds of times.

How to tell the difference? Fast recovery diodes have only two legs; The transistor has three legs.

Appearance: Diode with two legs. Transistor Three legs.

Function: Diode unidirectional conduction. Transistor amplification.

Connection: Diode There are two connection methods depending on the function. Transistor There are three ways to connect the transistor according to the function.

Bad question. The question should be asked, "What is the difference between a diode and a triode?" Or, "What's the difference between a quick recovery diode and other diodes?" ”

Electron diodes and electron transistors consist of a glass bubble pumped to a certain extent as a shell, and many new varieties have been derived later. Collectively known as electron tubes or vacuum tubes, they dominated radio for more than half a century. At present, in addition to being completely replaced by transistors (i.e., semiconductor tubes) and integrated circuits (ICs) in some occasions, they are still playing a role in high-power and other fields.