Dongguan QiMao Electronics Co., Ltd.

1. Chip with program

1. EPROM chips should not be damaged in general. Because this chip requires ultraviolet light to erase the program, it will not damage the program during testing. However, there is information: due to the material used to make the chip, with the passage of time (the age is long), it may be damaged even if it is not used (mainly refers to the program). So make backups as much as possible.

2. EEPROM, SPROM, etc., as well as RAM chips with batteries, are very easy to destroy programs. Whether this type of chip has broken the program after using the <tester> to scan the VI curve is still inconclusive. Nonetheless, colleagues should be careful when encountering such a situation. The author has done many tests, and the main reason may be: the leakage of the casing of the maintenance tools (such as testers and electric soldering irons).

3. For the chip with battery on the circuit board, do not easily remove it from the board.

Second, reset circuit

1. When there are large-scale integrated circuits on the circuit board to be repaired, attention should be paid to the reset problem.

2. It is best to put it back on the device before the test, and turn it on and off repeatedly to try it. And press the reset button several times.

Three, function and parameter test

1. <Tester> The detection of the device can only reflect the cut-off area, the amplification area and the saturation area. However, specific values ​​such as the level of operating frequency and the speed of speed cannot be measured.

2. Similarly, for TTL digital chips, only the output changes of high and low levels can be known. And it is impossible to find out the speed of its rising and falling edges.

Four. Crystal oscillator

1. Usually, it can only be tested with an oscilloscope (the crystal oscillator needs to be powered on) or a frequency meter.

2. Common faults of crystal oscillators are: 1) Internal leakage 2) Internal open circuit 3) Deterioration frequency deviation 4) Leakage of peripheral connected capacitors. The leakage phenomenon here can be measured with the VI curve of the <tester>.

3. Two judgment methods can be used for the whole board test: 1) During the test, the related chips near the crystal oscillator do not pass; 2) No other fault points are found except the crystal oscillator.

4. There are two common types of crystal oscillators: two-pin and four-pin, of which the second pin is used for power supply. Be careful not to short-circuit at will.

V. Distribution of fault phenomena

1. Incomplete statistics of faulty parts of circuit boards:

1) The chip is damaged by 30%,

2) Discrete components are damaged by 30%,

3) The wire (PCB coated copper wire) is broken by 30%,

4) The program is broken or lost by 10% (with an upward trend).

2. As can be seen from the above, when there is a problem with the connection and program of the circuit board to be repaired, there is no good board, neither is familiar with its connection, and the original program cannot be found. This board is unlikely to be repaired.