Common circuit board inspection and repair issues
Release time:
2023-03-29
Source:
1、 Chip with program
1. EPROM chips are generally not suitable for damage, as they require ultraviolet light to erase the program, so they will not damage the circuit board detection sequence using the WiFi microscope during testing. But there is information that: due to the materials used to make chips, even if not used, it may be damaged over time (mainly referring to the program), so it is necessary to provide backup as much as possible.
2. EEPROM, SPROM, and RAM chips with batteries are all highly susceptible to program damage. It is not yet certain whether these types of chips will damage the program after using the<tester>for VI curve scanning. However, colleagues should be cautious when encountering this situation. The author has conducted multiple experiments, and the possible reason is that the casing of maintenance tools (such as testers, soldering irons, etc.) leaks electricity.
3. Do not easily remove chips with batteries from the circuit board.
2、 Reset circuit
1. When there are large-scale integrated circuits on the circuit board to be repaired, attention should be paid to reset issues.
2. Before testing, it is best to reinstall the device, repeatedly turn on and off the machine to try it out, and press the reset button multiple times.
3、 Functional and parameter testing
1. The tester can only detect the cutoff region, amplification region, and saturation region of the device, but cannot measure the operating frequency and speed.
2. Similarly, for TTL digital chips, only high and low level output changes can be known, and the speed of their rising and falling edges cannot be detected.
4、 Crystal oscillator
1. Usually, it can only be tested with an oscilloscope (the crystal oscillator needs to be powered on) or a frequency meter, and cannot be measured with a multimeter. Otherwise, the substitution method can only be used.
2. Common faults of crystal oscillators include: a, internal leakage, b, internal open circuit, c, frequency deviation of deterioration, d, leakage of peripheral connected capacitors, and leakage phenomenon here. The VI curve of the<tester>should be able to detect it.
3. Two judgment methods can be used during the whole board test: a. During the test, the relevant chips near the crystal oscillator do not pass. b. No other fault points were found except for the crystal oscillator
4. There are two common types of crystal oscillators: a, two pin, b, and four pin. The second pin is powered on, so be careful not to short-circuit it randomly.
5、 Distribution of fault phenomena
1. Incomplete statistics of faulty parts of circuit boards: 1) 30% damage to chips, 2) 30% damage to discrete components,
2. The wiring (PCB board copper wire) is broken by 30%, and the 4 programs are damaged or lost by 10% (with an upward trend).
3. From the above, it can be seen that when there are wiring and program issues with the circuit board to be repaired, and there is no good board, one is not familiar with its wiring and cannot find the original program. The likelihood of this board being repaired is low.
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