1. Chip with program
1. EPROM chips are generally not damaged. Because this chip requires ultraviolet light to erase the program, it will not damage the program during the test.
However, there is information that due to the material used to make the chip, over time (the year is old), it may be damaged even if it is not used (mainly refers to the program). Therefore, it is necessary to back up as much as possible.
2.EEPROM, SPROM, etc. and RAM chips with battery are very easy to destroy the program. Whether this kind of chip will destroy the program after scanning the VI curve using
3. Do not easily remove the chip with battery from the board.
2. Reset circuit
1. When there is a large-scale integrated circuit on the circuit board to be repaired, pay attention to the reset problem.
2. It is best to reinstall the device before testing, turn it on repeatedly, try the shutdown machine, and press the reset button several times.
3. Function and parameter test
2. Similarly, for a TTL digital chip, it can only know the output change of high and low levels, and it is impossible to find out the speed of its rising and falling edges.
4. Crystal Oscillator
1.Usually you can only use the oscilloscope (the crystal needs to be powered up) or the frequency meter to test, the multimeter can't measure, otherwise you can only use the substitution method.
2. Common failures of crystal oscillators are: a. Internal leakage, b. Internal open circuit c.
Deteriorated frequency offset d. Leakage of externally connected capacitors. Here the leakage phenomenon can be measured using the VI curve of
3. Two kinds of judgment methods can be used during the whole board test: a. The relevant chips around the crystal oscillator failed during the test. B. No other fault points were 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, please be careful not to short circuit arbitrarily.
5. Distribution of fault phenomena
a. Incomplete statistics of circuit board faults:
1) chip damage 30%,
2) discrete components 30% damage,
3) The wiring (copper wire on the PCB board) is broken by 30%,
4) the program is broken or lost by 10% (there is an upward trend).
b. As can be seen from the above, when the circuit board to be repaired has problems with the connection and procedures, and there is no good board, you are not familiar with its wiring, and you cannot find the original program. It is unlikely that the board will be repaired.