Daily Maintenance And Common Problems Of Telephone Exchange（3）
The faulty circuit board can be repaired separately according to its circuit principle.
Control, common circuit board repair control unit circuit board, that is, CPU board, the first should check whether the fuse and components on the circuit board is intact, as well as the connection of each part of the printed circuit board; Then check the supply of power, that is, the working voltage of each chip; finally, the interface circuit chip and microprocessing chip can be replaced.
The fault processing of the whole keyboard board can be carried out by referring to the fault processing method of CPU board. When a single or several keys fail, you can look for fixes against the parameters of the rest of the normal keys. When the power supply circuit is normal, all kinds of signal sound circuits (bee sound, dial tone, etc.) can be decomposed into signal sound generator, control circuit and signal sound output circuit.
User, relay circuit board
The circuit board consists of ring control circuit, feed circuit, off-hook state and dial-up detection circuit, decoder and switch matrix circuit, overvoltage protection circuit. When the user calls into the ring, check the circulation circuit, especially the bell switch chip and the bell flow control chip. When the user can not dial, the focus is to check the detection chip and buffered chip. When the user has no feed voltage, checking the constant current power supply is mainly the transistor itself and its bias resistance. When the user has no dial tone and no call, if the user board (8 users) has a common fault, the switching module and control circuit of the user board should be checked, and the single user fault will check whether the coupled transformer of the user is open.
The power supply of SPC telephone exchange adopts primary and secondary power supply structure. One of the AC / DC module output 48V voltage is mainly to feed the user, but also as the input of the secondary power supply; the second DC / DC module output 5V / 12V voltage supply CPU control, common circuit part. If there is an overcurrent and overvoltage protection circuit in the circuit, the chip in the protection circuit should be removed first when the power supply is overhauled, so that the protection circuit does not work, and then the damage of each power supply is judged according to the voltage measurement. Because the power supply uses module structure, so maintenance power supply is very simple. Remove a small number of peripheral components after the failure factor, that is, the module itself fault.