Analysis of monitor structure and maintenance examples
The monitor is a system that can selectively carry out regular or continuous detection of important physiological and biochemical indexes of human body, and has the functions of storage, display, analysis and control, and alarm parameters beyond the specified range. Because it can monitor important life parameters of patients in real - time, continuously and for a long time, it has become a relatively large number of common equipment in hospitals, and the failure rate is relatively high. because most manufacturers do not provide circuit diagrams at present, it brings some difficulty to maintenance. Especially the imported monitor circuit board is expensive, so analyzing the fault to component level maintenance can save a lot of money for the hospital.
1 structure of medical monitor
Monitor manufacturers In order to quickly detect and remove faults, we must first understand the main structure and principle of the monitor. Then, the unit or multivariate analysis method is used to find out which unit the fault occurred in and further find out the faulty component.
The structure of the medical monitoring instrument is shown as follows: it is mainly composed of six parts: ( 1 ) power supply part, ( 2 ) signal detection part, ( 3 ) analog processing part of the signal, ( 4 ) digital processing part of the signal, ( 5 ) display and recording part of the signal, and ( 6 ) alarm part.
2 examples are given to illustrate the fault analysis and maintenance methods

2.1 Philips a3 monitor
Fault a: there is a white bright band scrolling up on the screen, the others are normal.
According to the preliminary analysis of the fault phenomenon, it seems that it is an interference fault. we first check the power supply circuit, and the AC filter has no abnormality, and then check the field scanning circuit for no abnormality. Causing maintenance to get into trouble. We carefully analyzed the fault phenomenon, found a fault-free machine of the same model, replaced the suspected circuit board with a test machine, and found that there was a problem with a small circuit board on the edge of the LCD screen. The main board output signal is used for LCD field display through this version. it is determined that the fault is in this version. we use a digital multimeter with waveform to carry out comparative measurement and find that there is an abnormal electrolytic capacitor. the fault is removed after replacement.
Fault b: the program control key on the panel fails, and the screen display is normal.
After checking that the spring leaf of the key in the key is elastically aged and cannot be ejected when pressed down, we will open the back cover of the key and take out the spring leaf, gently press it with the hand to restore the original elasticity of the spring leaf, pack it again in the reverse order, stick the back cover firmly with glue, and start-up test will return to normal.
Fault c: when measuring blood pressure, the pressurizing time of the air pump is too long, and the blood pressure can not be measured sometimes.
The fault mainly occurred on the motor and pump body. We must first judge whether the power supply circuit is faulty or the pump body is faulty. the measured power supply voltage is normal and the rotation of the motor is normal. the analysis problem lies in the pump body. the pump body is disassembled and the diaphragm is found to be broken, causing the air leakage of the air pump to fail to work normally. We use the domestic pump body to install on the original motor, troubleshooting.
Fault d: the power-on indicator is on, black screen, and pressing any key is invalid.
Since the power indicator is on, the power supply effect of the power supply is good. Focus on checking the main board. as there is no circuit diagram, first carefully check each component for any abnormal color change, deformation and heating. it is found that there is a patch of electrolytic capacitor color change. after online measurement by multimeter, there is no capacity, and after welding, the measurement has been disconnected. Do not rush to power on the test machine after replacement. To analyze the cause of the damage, we measured the other components according to the wiring of the circuit board and found a triode short circuit. after replacement, the monitor returned to normal.
Fault e: when measuring blood pressure, there is no air pump pumping sound and blood pressure cannot be measured.
The air pump has no air pumping sound, which is judged as a fault of the motor of the air pump or a fault of the power supply circuit of the air pump. Using a multimeter to measure the short circuit of the motor, it can be judged that the motor of the air pump is faulty. Open the rear cover of the motor and find that the brushes fall off and the two brushes touch each other. Reset and rearrange. adjust to 6v with a regulated power supply. the motor of the test air pump operates normally and the air bag is pumped well. The air pump installed back into the machine still does not turn to measure that there is no 6v voltage in the air pump power supply circuit. Following the test of the power supply circuit of the air pump, it was found that a current-limiting resistor was cut off, which may be caused by a short circuit of the brush. the current-limiting resistor was cut off and replaced. the blood pressure measuring circuit returned to normal.
2.2 mclaren pm - 9000 multi-parameter monitor
Fault a: unable to measure blood pressure, fault shows: " air pump leaks."
Analysis and maintenance: enter the air leakage inspection procedure, and the air leakage is detected. first, check whether the external pipeline and sleeve belt of the machine are air leakage, and the check is normal. Open the cabinet to check the air pump, pipeline and solenoid valve and find that the air bleed valve is leaking. The valve plate El is tightened, the inflation test is good, the electricity test machine is installed, and the blood pressure monitoring is normal.
Fault b: unable to take blood pressure measurement, fault shows: " wrong air pressure".
Analysis and maintenance: first, check whether the pipe and sleeve outside the machine are air - leaking, and then check whether there is any crack or air - leaking. Open the cabinet to check the air pump, pipeline and solenoid valve. the non-invasive blood pressure monitoring of the machine adopts the oscillation method. the start-up inflation time is normal and the pressure is normal. the slow-release valve gradually deflates slowly in steps. when the pressure drops to about 12k pa ( 90 mmhg ), the air release valve deflates suddenly and the blood pressure cannot be measured. The reason for the analysis is that the deflation time of the slow deflation valve exceeds the program preset, forcing the deflation valve to open and deflate. The resistance value of the slow-release valve coil measured is normal, and the power-on and suction are normal, but there is rust and dirt in the inlet water of the valve joint, which causes poor deflation, resulting in prolonged deflation. Troubleshooting after clearing.
2.3 photoelectric 6201 k monitor
Fault phenomenon: photoelectric signals are normally displayed on the screen, but the record cannot be fed.
The photoelectric 6201 k monitor recorder does not have a paper feeding motor protection circuit, which is often the key part of maintenance. The protection principle is as follows: when the current through the motor reaches its rated limit ( 300 Ⅱ la ), the sampling resistor r160 ( 2.2 ohms ) is connected in series. the voltage is applied to the base of q115 to turn it on, pulling the driving voltage of the motor to zero and stopping it from working, thus achieving the purpose of protecting the motor.
When troubleshooting this case, the resistance value of sampling resistor r160 is normal and the dynamic voltage is 0.65 v; The static voltage of 0v indicates that the control signal of this state is normal, but the paper cannot be fed is that the motor protection circuit is not working normally and can be improved on its circuit. That is, a 2.4 ohm resistor is connected in parallel to the r160 sampling resistor, and the resistor voltage drops to 0.3v when it is restarted, so that q115 cannot be conducted, the protection circuit is cut off, and the motor paper feeding is normal.