One, with the procedure of the chip
1, EPROM chip in general should not be damaged, because the chip needs ultraviolet light to wipe away the program, so in the test will not damage the circuit board testing process wifi. But there are information: due to the production of the material due to the chip, with the passage of time (long long), even if not also possible damage (mainly refers to the program), so as to give backup.
2, EEPROM, systems and RAM chips with battery, are very easy to damage to the program, this kind of chip whether use the < tester > of VI curve scanning, whether on the destruction of the program, is inconclusive, however, colleagues when encountered such a situation, or care for the wonderful. The author had many tests, possible reasons are: maintenance tools (such as tester, electric iron, etc.) of the casing leakage caused by.
3, for the circuit board with a battery of chips do not easily removed from the board.

Two, reset circuit
1, when there is a large scale integrated circuit on the circuit board to be repaired, attention should be paid to the problem of reset.
2, in the test before the best equipment on the back, repeatedly open, shut the machine to try, and press several reset button.

Three, function and parameter test
1, < tester > of the device detection, can only reflect the cut-off area, enlarge the area and saturation area, but can not measure the frequency of high and low speed and the speed of the.
2, similarly to the TTL digital chip, it can only know that there are high and low level of output change, and no way to detect its rise and fall along the speed.

Four, crystal oscillator
1, usually only used oscilloscope (crystal needed to power up) or frequency meter, multimeter to measure, otherwise only the substitution method.
2, common crystal fault: A, internal leakage, B, internal open C, metamorphic frequency partial D, the external connected electric leakage, leakage phenomenon here, < tester > VI curve should measure.
3, the whole board test can be using two methods: A. test of crystal near around the chip does not pass through. In addition to crystal did not find fault.
4, there are 2 common crystal: A, B, four feet, second feet, which is the power supply, not to be taken with a short circuit.

Five, the distribution of the fault phenomenon
1, circuit board fault parts of incomplete statistics: 1) chip damage 30%, 2) discrete components damage 30%,
2, the connection (PCB board deposited copper wire) break 4, 30% program damage or loss of 10% (there is an upward trend).
3, from the above we can know, when the circuit board to be repaired and the program has problems, and no good board, neither familiar with its connection, can not find the original program.