Medical Equipment Repair: Common ECG Machine Malfunction Repair

Introduction to Fully Automatic Electrocardiograph

The bioelectrical changes of the heart itself are reflected on the body surface through the conductive tissues and body fluids surrounding the heart, causing regular electrical changes in various parts of the body during each cardiac cycle. When the heart is damaged or necrotic due to ischemia, the changes in electrocardiographic activity can be accurately and timely reflected on the electrocardiogram, manifested as abnormal changes and progressive evolution of various waveforms, providing doctors with a reliable basis for diagnosing cardiac diseases such as arrhythmias, ventricular hypertrophy, acute ischemia, and myocardial infarction.

Internal Structure

The electrocardiograph consists of three parts: a galvanometer, an amplifier, and a recorder. It consists of a main unit and many lead wires and electrode plates. The lead wires are marked with different colors such as red, yellow, green, black, and white to distinguish the negative pole.

Common Malfunctions and Repair Solutions

Malfunction: The power indicator light does not light up after power on, and the machine cannot be turned on.

Detailed Cause of Malfunction:① Poor contact or damage to the power cord connector and power plug

② Power switch damage

③ Power fuse blown

Unable to print results:The printing mechanism's drive gears are poorly meshed or damaged, or there is a foreign object stuck in the drive mechanism.

Repair or replace gears

Abnormal waveform when patient is connected to ECG leads:① ECG lead wire is damaged, broken, or poor contact between the lead wire and the electrocardiograph

② Poor contact between the patient's limbs and the suction cup, dry skin.

③ Poor contact between the patient's limbs and the suction cup, dry skin.

Automatic shutdown after power on:① Check if the battery has power and if AC power is connected. Ensure normal power supply.

② Check if the optocoupler, 431, and capacitor on the power supply board are damaged. Generally, it is due to the degradation of their performance that causes abnormal circuit operation.

No ECG waveform is recorded, but the ECG signal of the pen is normal, and the paper feed speed is normal:① The temperature of the recording thermal pen is too low

② The heating resistance wire of the pen is burned out

③ Poor contact between the recording pen and the recording paper

④ Self-excited multivibrator stops oscillating

⑤ Pen temperature is too high

No millivolt calibration signal, pressing the standard voltage switch does not work

① Millivolt standard voltage switch contact damage

② Photosensitive transistor in optocoupler damaged

③ Insufficient voltage of the standard battery

④ Differential amplifier or closed circuit malfunction.

The recording pen single-sided baseline adjustment knob does not work

① Poor contact at the peak connection of the position sensor signal

② DC amplifier malfunction in the preamplifier circuit

③ High-gain amplifier malfunction

④ Light-emitting diode in the optocoupler is damaged

⑤ Differential amplifier malfunction.

Baseline drift

① Patient limb movement; affected by surrounding electromagnetic waves

② Poor contact of the lead wire plug or excessive pulling of the lead wire;

③ Instrument aging or malfunction of electronic components.

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