1. Make a preliminary analysis of the fault
The general steps of fault analysis are as follows:
(1) circuit board fault phenomenon (ask the repair personnel).
(2) According to the failure of the phenomenon of a preliminary analysis of the possible fault distribution.
(3) according to the circuit board function area division to make a simple fault flow chart.
(4) Check step by step according to the fault flow chart, which is very beneficial to accumulate judgment experience.
In addition, it is necessary to record the whole maintenance process after fault repair, and organize relevant maintenance data to guide the maintenance in the future.
2. Prepare the necessary tools and information
(1) Prepare necessary measuring instruments, such as: maintenance tester, multimeter (digital/pointer type), short circuit tracker, programmer, EPROM eraser, signal generator, frequency meter, storage oscilloscope, logic analyzer, etc. Prepare necessary maintenance tools, such as tweezers, IC extractors, wire cutters, diagonal cutters, anti-static gloves, dust cleaning ear balls and brushes, non-inductive screwdriver, electrostatic pen, electric soldering iron, tin absorbers, hot air gun, constant temperature soldering station, etc.
The preparation of commonly used components, such as: TTL series, COMS series, commonly used memory series, common LSI series, commonly used interface device series, commonly used analog switch series, etc. Also prepare a series of resistors (resistor rows), capacitors, inductors, transistors, etc.
(3) before maintenance should be sent to repair personnel to understand the fault circuit board damage process, as well as in the equipment diagnosis report, which is very important to correctly and effectively judge the fault.
If conditions allow, the maintenance personnel had better go to the site to actually see the fault phenomenon, to determine whether there is indeed a fault sent to repair circuit board. That is to confirm whether the circuit board is connected correctly, firmly inserted, whether there is no change in the setting, the steps of operating equipment is correct, many good circuit boards are often due to the operator's lack of experience and was misjudged as a fault.
(4) before maintenance, it is best to understand the fault circuit board in the normal state of each test point of logic level, logic waveform, etc., at least to understand the function and use of each main device, ready for the device parameters manual, etc., ready for reference and analysis at any time.
(5) before testing power, to figure out the fault circuit board power type, positive and negative polarity, vulnerable devices and whether there is a short circuit, missing parts and other problems, the first power test to be careful, so as not to add the wrong power burn out the board.
3. The same circuit board is very valuable for fault repair
The maintenance personnel should be able to request the maintenance unit or repair personnel to provide a good circuit board or a bad circuit board that is exactly the same as the fault circuit board.
In the current component level maintenance, many test instruments are equipped with a relatively strong good and bad circuit board component comparison function. A good circuit board is sometimes far more valuable to successful repair than a circuit diagram, greatly increasing the speed of repair and the rate of a single repair.
The broken PCBA board which is exactly the same as the fault circuit board is also of great reference value for maintenance. Because two broken circuit boards may not have the same fault point, even if the fault point is the same, the extent of damage may not be the same. Therefore, it is often easier and more convenient to repair several identical broken circuit boards simultaneously than to repair a single broken circuit board.