dental unit, with one set of PC system each for the unit and the chair. The PC on the machine controls the on/off switch of the shadowless lamp, mouthwash, water heating, phlegm basin flushing, call system, and observation lamp, as well as the time adjustment of mouthwash and phlegm basin flushing. The PC on the chair controls the up, down, forward, and backward movements of the dental chair, as well as the storage of three preset chair positions. The patient chair is driven by a DC motor and has low noise.
Check that the bulb of the dental unit is not broken and the power supply is normal. Remove the connection between the lamp arm and the lamp fixture and find that the plug connecting the internal wire of the fixture and the arm has become discolored and loose, causing poor contact. The reason for this is that the shadowless lamp works under low voltage and high current, so the plug socket may become hot and oxidize after prolonged use, resulting in this fault. Solution: replace the new plug socket. If there is no condition for replacement, temporarily cut off the plug socket of the wire and connect the two wire ends directly, wrap them well-insulated, reinstall the lamp fixture, and put it into use.
After removing the lamp arm and connecting it to the lamp fixture, we found that the internal wire of the lamp had been twisted into a bunch and was torn off. The reason for this: the early product of the shadowless lamp did not have a left and right rotation limit, resulting in this fault caused by always rotating in one direction. Solution: rotate the lamp fixture in the opposite direction to loosen the twisted wire, find the open circuit (or short circuit), reconnect and insulate it. If the wire is severely damaged, replace it with a new one. After the treatment is completed, the operator should be informed of the correct use method.
Check that the power and gas supply are normal. Press the up, down, forward, and backward keys, but the dental chair does not move. Remove the front cover of the patient's chair and check the AC24V and AC12V wiring terminals on the circuit control board, and the voltage is normal. Then check that the control circuit pneumatic switch is not closed, resulting in the control circuit not being connected. The reason: the screw of the fixed pneumatic switch is loose, and the gas valve cannot effectively press down the travel switch. Solution: readjust the distance between the pneumatic valve and the travel switch to ensure that the travel switch can reliably connect under the rated air pressure, and then tighten the screw.
Press the up, down, forward, and backward keys of the dental unit, and you can hear the sound of the relay contactors, but the chair does not move. This phenomenon indicates that there is no problem with the control circuit. Check that the AC24V and AC12V are normal. AC12V is the power supply for the control circuit, and AC24V is the power supply for the DC motor. Check the rectifying voltage, there is no DC24V output. Observing the circuit control board, we found burn marks near the DC24V rectifier bridge. Measuring shows that two arms of the rectifier bridge have been broken down. Because there is no DC24V power supply, although the relay contactors are attracted, the chair does not work because the motor cannot get power.
Press the up, down, forward, and backward keys of the dental unit, and the chair does not move and there is no sound of relay contactors. Remove the front cover and check that the AC/DC power supply is normal, all plugs and connections are not loose, and the pneumatic switch is connected well. At this time, check whether the signal line of the button is normal. Test method: unplug the signal line plug on the circuit control board, connect one end of a wire to the black wire socket, and touch the other electrode of the socket with the other end to observe if the relay contactors move and whether the corresponding indicator light is on. If it is normal, there may be a problem with the signal wire; the most likely cause is that the black wire is shared, and the fault point can be found for processing. If the relay contactors do not move during the test, it means that the control board is faulty and can be replaced.