【 Weak current College 】 electronic detection and replacement experience (2) 】

Third, the transistor's testing and experience.
Circuit transistor has crystal diode, transistor, MOSFET SCR and so on, one of the most commonly used is the transistor and diode, how to properly judge, triode or bad, is one of the maintenance key.
1 Crystal diode: first of all we want to know the diode is silicon tube or pipe-germanium, germanium pipe forward voltage drop General 0.1 volts ~ 0.3 Volt, silicon tube General 0.6 volts ~ 0.7 volts. Measurement method: measurement with two multimeter, when a multimeter measuring the resistance of its forward while the other multimeter measuring its pipe pressure drop. Last may, under its authority to judge the value of pressure drop is Silicon Germanium pipe or tube. Silicon tube available multimeters to measure R×1K retaining, germanium tube available R× 100 block to log. In General, the measure of diode forward and backward between the more disparity between the resistance, the better. General as forward resistance to several hundred to several thousand euro, reverse resistance to tens of thousands of euro or more, you can determine this diode initially is good. While judgment diode polarity, when the measured resistance to hundreds or thousands of Central Europe, the diode forward resistance, then take the table amount received as a negative, as reported in the table amount as the cathode. In addition, if you are reverse resistance is infinite, which means that its internal breakage; forward and backward resistance as big, this diode has a problem; forward and backward resistance is zero indicates a short circuit.
2 transistor triode: predominantly Zoom effect, then how to sentence the zoom capacity measured triode? it is multimeter to R× 100 block or block, when measuring R×1K NPN-type tube, as table amount received emitter, negative table pen pick set electrode, the resistance should generally be measured as more than a few thousand euro; and then in the base and the collector thread between a 100 thousand European resistance, multimeter measured resistance should be obvious, the larger the variation, the transistor's zoom capability, if you change very little or no change, it shows the ability of the transistor is not zoom in or zoom capability is weak.
Electrode judgment method
Measurement of Germanium pipe R * 100 stalls, Silicon tubes R * 1k stalls first fixed red table pens and one foot in contact with, the black table amount for the remaining two foot measurement. If we can find two small resistance, if not longer to red table moves the pen to the other foot continue to measure care to two small resistance, if fixed red line not find two small resistance, pens can be fixed black table continue to find it.
When you find two small resistance, the fixed amount of a table is used by the base. If a fixed table pen to black pen, the transistor NPN-type, for fixed as red pen, the tube is PNP.
A judgment ce very resistance method
Multimeter measurement in addition to the base extremely polarized resistance, exchange table pen test twice, if this is the GE Canal, measuring resistance smaller once, if PNP type, measuring the black table amount received for the emitter, red table amount received is the collecting electrode, if measured for NPN-type, the black table amount for the collecting electrode, red table amount is received; if the emitter is silicon tube, the larger of measuring resistance once, if PNP type, measuring the black table amount received for the emitter, red table amount received is the collecting electrode, if measured for NPN-type, the black table amount for the collecting electrode, red table amount received is emitter.
BPN-forward resistance method
Respectively measuring two pn junction is the resistance, the larger the emitter, smaller for the collector.
C amplification coefficient method
Multimeter for two table pen and the base exception two foot contact, if PNP, the fingers touching base with red pens are a great look at the situation, pointer swing and then exchange table pen testing, to pointer oscillations of a time, then, the next red table pens for collecting electrode; NPN, the fingers touching base with red pens are a great look at the situation, pointer swing and then exchange table pen testing, to pointer oscillations of a time, at this point, the black table amount as a collector.
Note: analog and digital simulation of distinction, table table red table amount received is the power of negative, while the number table instead.
Fourth, inductors, transformers detection methods and experience
1 color code inductors in the multimeter in R× 1, red, black table pen the next color code inductors any terminations, at which point the pointer to the right. According to the measured resistance values, specific points in the following three conditions for identification:
A measured color code inductor resistor value is zero, its internal short circuit fault.
B the measured color code inductors DC resistance of size and wound inductors coils of wire diameter, wound coils are directly related to detect resistance values, you can view the measured color code inductor is normal. 
2 weeks transformer testing
A call to the multimeter R× 1, in accordance with the winding of the transformer week pin arrangement pattern, check-off of the windings, and determine whether it is normal.
B detect the insulation properties of the multimeter in R×10k, do the following State:
(1) the primary winding and secondary winding resistance value between;
(2) the primary winding resistance between the case;
(3) secondary windings and shell between resistance values.
The above test results in three situations:
(1) resistance to infinity: normal;
(2) resistance to zero: a short circuit fault;
(3) resistance less than infinity, but greater than zero: the leakage of the failure. 
3 power transformer testing and experience
Its easy to wrong mainly for internal short circuit. You can then check the supply voltage via a multimeter to determine whether it is normal, if output transformer insulation performance degradation or turn to local short circuit, making row scan current surges, switching power supply output voltage drop. Thus, by measuring the voltage to determine output transformer is shorted.
A through observation of transformer looks to check whether there is an obvious exception. Such as whether or not broken, the coil wire solder, insulating materials have burned traces,Fastening screw for iron, silicon steel sheet has no corrosion, winding coils for exposure, etc.
B insulation testing. Multimeter measure R×10k retaining core and primary, junior and secondary, core and all subordinate, electrostatic shielding layer and the cha secondary and secondary winding resistance value between, multimeter pointer should refer to the location in the infinity. Otherwise, the transformer insulation performance.
C coil-off detection. The multimeter in R× 1, tests, if a winding resistance value is infinite, then the winding circuit breaker failure.
D identifying primary and secondary coils. Power transformer primary pin and PIN are generally leads from both sides respectively, and the primary winding more words marked with 220V, secondary windings are marked rated voltage values, e.g. 15V, 24V, 35V, etc. Then, based on these tags to be identified.
E-load current detection.
(A) direct measurement. All the secondary winding all open circuit, the multimeter in AC current 500mA, string retainer (into the primary winding. When the primary winding of the plug 220V AC 220V 50 Hz, the multimeter is indicated by the no-load current value. This value should not be greater than the current transformer with a 10 per cent to 20 per cent. Common electronic device power transformer of normal no-load current should be about 100mA. If you exceed too much, the transformers have a short circuit fault.
(B) indirect measuring method. In the primary winding of the transformer in a series of resistors 5W 10/, secondary still all unloaded. The multimeter to AC voltage. Powered by two table amount measured resistance R at both ends of the voltage drop U, and then use Ohm's law to work out the empty-load current, i.e. I I empty = U/R.

F no load voltage detection. The power transformer primary next 220V multimeter AC voltage received by various tests of no-load voltage values (U21, U22, U23, U24) should meet the requirements, the scope is normally allowed error: high voltage windings ≤ ± 10%, and low voltage windings ¡ü ¡à 5%, with Center-tapped two symmetric difference of the voltage windings should be ≤ ± 2%.

G General small power transformers allow temperature to 40 ℃ ～ 50 ° c, if the insulation quality is better, allow temperature can also be improved.
Distinguishing the winding H detection with the client. When using the power transformer, sometimes in order to get the required secondary voltage, you can combine two or more of the secondary winding-up and use. In-line method using power transformers, participate in the windings in series with the same name-end must be connected correctly, you cannot make a mistake. Otherwise, the transformer is not working properly.

I. power transformer short circuit fault discriminant of comprehensive testing. Power transformer short circuit fault after symptoms are fever, severe and secondary winding of output voltage. Typically, the internal coil turn to turn short-circuit the more points, the greater the short circuit current, while the more serious the transformer fever. Detect whether there is a power transformer judged short-circuit fault of simple method is to measure the no-load current (test method described earlier). There is short circuit fault of transformers, the no-load current value is far greater than 10 per cent of the full load current. When a short circuit, transformer in no-load powered tens of seconds willrapidly heating, hands to touch the core will be hot. Without measuring no-load current transformers can be concluded that the short point exists.
5. integrated circuit block
To judge the quality of the integrated circuit block, all available multimeter measuring manifold blocks on foot of supply voltage, ground resistance values and the operating current is normal. You can also remove the manifold, measuring the feet and earthing circuit block feet between the resistance is normal, when removing the manifold can measure the external circuit to the foot of the resistance value is normal. To note is that the replacement of the integrated circuit block, it is important to note that the quality of welding and welding time. In replacement of the integrated circuit block General requirements under the same model, with the specifications of the integrated circuit to be replaced. It cannot find the original model, the specifications of the integrated circuit block, consider using similar features integrated circuit block in place, but it is important to note that when you want to know the place of the supply voltage and impedance matching, pin position and the external control circuit.