In order to improve the test effect, some technical treatment of the plate should be done before the on-line functional test of the circuit board to minimize the impact of various disturbances on the testing process.
The specific measures are as follows:
1. Preparation before testing Short-circuit The crystal (note that the crystal vibration of the four feet to understand that the two feet for the signal output foot can short-circuit these two feet.) Remember that in general the other two feet for the power supply foot must not be short pick!!) For large-capacity electrolytic capacitors also need to weld a foot to make it open.
Because the charge and discharge of high-capacity capacitors can also cause interference.
2. Test the device using an exclusion method If the device is tested online or compared to a device that is tested (or more normal) during the test, please confirm the test results directly for the record. The test failed (or compared to the variance) can be tested again. If you still do not pass, you can confirm the test results first. So keep testing until the device on the board is tested (or compared).
Then deal with those devices that have not passed the test (or compare the variance).
Some test instruments for devices that do not pass the functional online test also provide a less formal but more practical way to do this: since the power supply of the circuit board of the test instrument can also be applied to the corresponding power supply and ground foot of the device by means of a test clip, the device will be detached from the circuit board power supply system if it is applied to the device's At this point, the device is tested for online functions, and the interference is eliminated due to the fact that other devices on the circuit board will not get electrical work. At this point, the actual test effect will be equivalent to the "quasi-offline test" measurement rate will be greatly improved.