Several Simple Methods for Testing IC Chips with a Multimeter
① Offline Detection
Measure the forward and reverse resistance between each pin of the IC chip and the ground terminal. Compare the measured resistance values with those of a qualified normal IC chip to accurately locate fault points.
② Online Detection
1) DC Resistance Detection Method
The operation method is consistent with offline detection. The following precautions must be observed:
(a) Cut off the power supply of the circuit board under test;
(b) Ensure the internal voltage of the multimeter does not exceed 6 V;
(c) Avoid the interference of peripheral circuit components such as potentiometers connected to the IC chip during measurement.
2) DC Operating Voltage Measurement Method
Compare the measured DC voltage of each IC pin with the standard normal voltage value. Relevant precautions are as follows:
(a) The multimeter must have high internal resistance; a digital multimeter is the preferred choice;
(b) Adjust all potentiometers to the middle position before testing;
(c) Take anti-slip measures for test probes. A bicycle valve core can be sleeved on the test probe, extending about 5 mm beyond the probe tip;
(d) If the measured voltage is inconsistent with the standard value, analyze the influence of the abnormal pin voltage on the IC operation and the corresponding voltage changes of other pins comprehensively;
(e) IC pin voltages are easily affected by peripheral component faults, including electric leakage, short circuit, open circuit and component aging;
(f) When individual IC pins show abnormal values, start troubleshooting from the pins with the maximum deviation. Check peripheral components first; if no fault is found, the IC chip is damaged;
(g) For circuit boards with dynamic operating signals, IC pin voltages vary with signal changes. Abnormal voltage fluctuations indicate potential IC chip failure;
(h) For equipment supporting multiple operating modes, the IC pin voltage values differ under different working modes.
3) AC Operating Voltage Test Method
Use a multimeter with a dB gear to measure the approximate AC operating voltage of the IC. If the multimeter is not equipped with a dB gear, connect a 0.1–0.5 μF DC blocking capacitor in series with the positive test lead. This method is applicable to ICs working at low frequencies. Since the measured signals are affected by inherent frequency and waveform differences, all test data are approximate and for reference only.
4) Total Current Measurement Method
Judge the working condition of the IC by measuring its total power supply current. Most internal circuits of ICs adopt DC coupling mode. When the IC is damaged (such as PN junction breakdown or open circuit), the subsequent circuit stage will be saturated or cut off, resulting in a change in the total operating current. Therefore, the quality of the IC can be judged by detecting the total current. The current value can be calculated by measuring the voltage drop across the loop resistance in the online circuit.
