【 Weak current College 】 common circuit repair basics "2" 】

Measure the time it should be noted that, due to the manifold internal has a large number of transistors, diodes and other nonlinear components, the measurements of a single measured resistance also cannot determine its good or bad, you must swap sheet pen and then measuring time, access to the forward and reverse two resistance. Only when the resistance R of forward and backward are up to standard, to conclude that the manifold blocks intact. In the actual repair, usually measured in the road. First measure their PIN voltage, if voltage anomalies, to disconnect pin wiring terminals voltage measured to determine voltage variation is caused by external components or manifold internal cause. Or you can use logging to an external circuit between the DC equivalent resistance (known as R), usually measured in the circuit of the manifold blocks a PIN and grounding feet between the DC resistance (in road resistance), R R-parallel within the total DC equivalent resistance. Often the repair will be at the road, voltage and resistance in the road measurement method. Sometimes the road voltage and resistance in the road, and deviations from the standard value is not necessarily the manifold damage, damage to the peripheral component, R, not normal, resulting in the road, voltage and resistance in the road. You can only measure the manifold internal DC equivalent resistance to determine manifold damage.
According to the actual maintenance experience in detecting IC internal DC equivalent resistance when you don't have to put the manifold from circuit welding down, voltage or road resistance anomalies feet and the circuit, at the foot of the ground is also disconnected from the circuit board and other foot to maintain the status quo, measuring out test feet and earthing pin R between forward and backward resistance values within will be judged good or bad. For example, TV in the manifold TA7609P Rong feet in abnormal voltages or resistance, can cut off the feet and legs ⑤rong (grounding feet) and then use the multimeter measuring suvey in rong feet and ⑤ feet measured between the resistance, a numeric, interchangeable table pen and then test it again. If the manifold measured normal to red table for the pen grounding 8.2 k Ω, the black table amount at the time of the grounding of 272 k Ω r equivalent resistance in DC, manifold block is corrupted.
In the measurement of most pins, multimeter with R×1k, when individual pin within very large R, swap R×10k block, this is because the table R×1k retaining battery voltage only 1.5V, when manifold internal transistor series more, electricity meters in the voltage is too low, not for manifold block access to work correctly in the transistor, numerical cannot show or inaccurate. In short, in the detection time to serious analysis, flexibility in the use of various methods, rules, do it quickly and accurately identify the failure.

IC testing experience
(A) common detection method
IC detection methods are commonly used in online measurement, non-online measurement and substitution method.
1. non-online surveys-online surveys-tide in the integrated circuit is not welded into the circuit, by measuring its PIN DC resistance between the known and the same model and integrated circuits between the PIN DC resistance in comparison to determine whether it is normal.
2. online measurement online measurement method is the use of voltage measurements, resistance measurement method and current measurements, measurement of the circuit integrated circuits on the PIN voltage, resistance values and current values are normal, to determine whether the integrated circuit is damaged.
3. substitution method for the substitution method is with a known good with the models, with the specifications of the integrated circuit to substitution can be integrated circuit, figure out the integrated circuit is damaged.
(Ii) detection of common IC
1. microprocessor IC testing microprocessor IC key test PIN is VDD power supply side and RESET Reset client, XIN crystal oscillator signal input, the output signal XOUT Crystal and other line input and output. On the road to measure these critical feet of resistance and voltage value and see whether normal (accessible from the product information concerning the maintenance of the circuit diagram or identified) are the same. Different types of microprocessor RESET Reset voltage is not the same, some low level reduction, i.e. post instantly to low level, and reset to maintain a high level; the high level reduction, i.e. Switch instantly to high level, and reset a low level.
2. the detection of switching power supply integrated circuit switching power supply integrated circuit voltage is key to feet (VCC) power supply side, encouraging pulse outputs, voltage measuring input, input current detection. Measure the PIN-to-ground voltage value and resistance values, and the difference between the normal value, in its peripherals normal cases, you can determine whether the integrated circuit has been corrupted. Built-in high power switching valve's thick film IC, also available through measuring switch tube C, B, E very positive, between reverse resistance value, to determine whether the normal switching tube.
4 maintenance basics
3. audio amplifier IC detection check audio amplifier IC, you should test its power (power side and negative power supply), audio input, audio output and feedback of the end-to-voltage and resistance values. If the measured value of the PIN and the difference between the normal value of data is big, its external components and normal, is an integrated circuit internal damage. On a silent failure caused by audio amplifier IC, power supply voltage measuring it correctly, the available signal interference method to check. Measurement, multimeter R× 1 should be placed in the red table pen, pen with black table dianchu audio input, the normal speakers should have strong "Titicaca" sound.
4. operational amplifier IC testing multimeter measuring DC voltage rail, output op amp with negative power supply-voltage values between (in static voltage value is higher). For hand-held metal tweezers then dianchu operational amplifier of the two input terminals (join the interference signal), multimeter hands relatively substantial swing, the operational amplifier intact; if multimeter table fixed needle, the operational amplifier is corrupted.
5. time base IC testing time base integrated circuit containing the digital and analog circuit, the multimeter is difficult to directly measure the good or bad. Can be used as in Figure 9-13 test circuit to test the timebase IC is good or bad. Test circuit resistor, light emitting diode, LED, 6V DC power supply, power switch S and 8 foot IC socket. The time base integrated circuits (for example NE555) IC socket plug letter by pressing and holding the power switch S, if the measured time base setInto a circuit, light-emitting diode LED will blink light emitting LED does not light up; if so, or have been lit, it indicates the measured time base integrated circuit performance.
IC substitution skills
I. direct substitution
Direct substitution is defined with a different IC without any changes and direct replace original IC, substitution has no effect on the machine after the main performance and targets.
The substitution principle is: substitution functionality of IC, performance indicators, package, PIN, the PIN number and spacing, and other aspects are the same. Which function the same IC refers not only to the same function; it should also be noted that the same logic, that is, the output polarity input level polarity and voltage, current ranges must be the same. For example: image in the IC, TA7607 and TA7611, the former to back high on AGC, the latter to put forward higher, AGC no direct replacement. In addition there is also an output voltage of different polarity AFT, the output of different polarity synchronization pulses and other IC can direct substitution, even in the same company or manufacturer of the product, should pay attention to distinguish. Performance indicators refers to the IC's main electrical parameters (or main characteristic curve), maximum dissipation power, maximum working voltage, frequency and signal input and output impedance parameters similar to the original IC. Power small surrogate thing to increase the heat sink.
1. the substitution of the same type IC
Replacement of the same type IC is generally reliable, the installation of integrated circuits, it is necessary to pay attention to direction and don't make a mistake, or the power IC may be destroyed. Some single in-line amplifier IC, type, function, characteristics are the same, but the direction of the PIN order is different. For example, 2-channel power amplifier ICLA4507, its PIN "is" or "anti", its starting feet annotation (color or pit) direction different; there is no suffix suffix is "R", IC, etc., for example M5115P and M5115RP
2. substitution of different models of IC
⑴ model prefix letters the same, different IC substitution. This kind of substitution as long as their PIN function exactly the same, its internal circuits and electrical parameters slightly, but also mutual direct substitution. Such as: sound in ICLA1363 and LA1365, the latter than the former at the IC No. ⑤ foot inside a Zener diode, exactly the same.
⑵ model prefix letters is the same as different, digital IC of substitution. In General, the prefix letter represents manufacturers and circuit of categories, the numbers following the prefix is the same, most direct substitution. But a few, although the numbers are the same, but the functionality is completely different. For example, HA1364 is sound IC, IC uPC1364 is color decoder; 4558, 8 feet of the operational amplifier NJM4558, 14 foot is CD4558 digital circuits; therefore they cannot be substitution.
⑶ model prefix letters and numbers are different IC of substitution. Some manufacturers introduce not encapsulated by the IC chip, and then processed into a press plant named products. There are such as to improve certain parameters indicator and improve products. These products are commonly used to name different models or distinction with designation suffix. For example, AN380 and direct substitution uPC1380; AN5620, TEA5620, DG5620 etc can direct substitution.

Second, non-direct substitution

Non-direct substitution is not a direct substitution of IC slightly modified the external circuit, changed the original pin arrangement or increase or decrease in individual components such as IC can be substitution.
Substitution principle: replacement of the IC can be used with the original IC PIN feature different, beautiful, but the functionality is the same as the character to be similar; after the substitution shall not affect the original machine performance.
⑶ the supply voltage to the IC and substitution, if the original circuit power supply voltage is high, should seek to buck; voltage low, to see whether the substitution of IC.
⑷ substitution for future measurement IC static operating current, if current is much larger than normal, the circuit may produce self-excited, decoupling, should be adjusted. To gain and original differences, you can adjust the feedback resistor;
⑸ substitution after IC input and output impedance to match with the original circuit; check their driving ability.
⑹ in changes in order to take advantage of the original Board foot hole and leader, external lead requirements in order to avoid before and after the cross in order to check and prevent the circuit since stress, especially to prevent the high frequency of self-excited;
(7) in power before the power supply Vcc loop thread again best in a DC ammeter, Buck resistor from big to small observation IC total current changes correctly.