1. Chip with program
1. EPROM chips are generally not suitable for damage. Because this kind of chip needs ultraviolet light to erase the program, it will not damage the program during the test. However, there is information: due to the material used to make the chip, as time goes by Long), even if it is not used, it may be damaged (mainly refers to the program). So it is necessary to back it up as much as possible.
2. EEPROM, SPROM, etc., as well as RAM chips with batteries, are very easy to destroy the program. Whether such chips will destroy the program after using the <tester> to scan the VI curve is not yet conclusive. However, colleagues When we encounter this kind of situation, it is better to be careful. The author has done many experiments, and the most likely reason is: the leakage of the shell of the maintenance tool (such as tester, electric soldering iron, etc.).
3. For the chip with battery on the circuit board, do not remove it from the board easily.
2. Reset circuit
1. When there is a large-scale integrated circuit on the circuit board to be repaired, attention should be paid to the reset problem.
2. Before the test, it is best to put it back on the device, turn on and off the machine repeatedly and try it. And press the reset button several times.
3. Function and parameter test
1. <Tester> can only reflect the cut-off area, amplification area and saturation area when detecting the device. But it cannot measure the specific values such as the operating frequency and the speed.
2. In the same way, for TTL digital chips, only the output changes of high and low levels can be known, but the speed of its rising and falling edges cannot be detected.
4. Crystal oscillator
1. Usually only an oscilloscope (the crystal oscillator needs to be powered on) or a frequency meter can be used for testing, and a multimeter cannot be used for measurement, otherwise the substitution method can only be used.
2. The common faults of the crystal oscillator are: a. internal leakage, b. internal open circuit, c. variable frequency deviation, d. leakage of peripheral connected capacitors. The leakage phenomenon here should be measured by the VI curve of <tester>.
3. Two judgment methods can be used in the whole board test: a. During the test, the related chips near the crystal oscillator fail. b. No other fault points are found except the crystal oscillator.
4. There are two common types of crystal oscillators: a. two pins. b. four pins, of which the second pin is powered, and attention should not be short-circuited at will. Five. Distribution of fault phenomena 1. Incomplete statistics of faulty parts of the circuit board: 1 ) chip damage 30%, 2) discrete components damage 30%,
3) 30% of the wiring (PCB coated copper wire) is broken, 4) 10% of the program is damaged or lost (there is an upward trend).
2. It can be seen from the above that when there is a problem with the connection and program of the circuit board to be repaired, and there is no good board, not familiar with its connection, and cannot find the original program, the possibility of repairing the board is not great.
Post time: Mar-06-2023