Using voltage inspection method to quickly locate fault points in integrated circuits

The voltage inspection method is the most effective and commonly used inspection method for checking integrated circuits. As the voltage inspection method is measured in parallel and does not require circuit changes, it is quite convenient to operate.

The voltage inspection method is used to determine the fault point as follows:

(1) The general voltage inspection method mainly measures the DC voltage of key test points in integrated circuits, and may also measure AC voltage if necessary. When inspecting, it is important to focus on checking the voltage of key test points in the circuit, which mainly include the power supply pin, signal input pin, and signal output pin of the integrated circuit, as well as the DC voltage on some important control pins.

(2) When there is no standard operating voltage data for each pin of the integrated circuit to be checked, the characteristics of the peripheral circuits of each pin should be used to distinguish obvious abnormal phenomena in the pin voltage. When it is difficult to determine, you can find another electrical device of the same model and compare and analyze it by measuring the DC voltage of each pin of the integrated circuit in the same part. The results of this inspection method are very accurate.

(3) When there is an abnormal voltage at the pins of an integrated circuit, only the capacitor needs to be suspected of breakdown or leakage, the inductor needs to be suspected of open circuit, and the resistor needs to be suspected of open circuit and short circuit.

(4) When the voltage of multiple pins in an integrated circuit changes simultaneously, it is often caused by a fault, because the circuits in the integrated circuit are directly coupled between each level, and the DC voltage between each level of circuit will affect each other. If the connection pins between the integrated circuit and other circuits are coupled by resistance capacitance, the voltage deviation fault of each pin is caused by the integrated circuit itself. If the input or output terminals are directly coupled (without DC blocking capacitors), it is also possible that the DC voltage deviation of multiple pins of the integrated circuit is caused by a fault in the front-end or back-end circuit.

(5) The DC working voltage of the integrated circuit power pin is abnormal (usually lower than normal). If the voltage of other pins is also abnormal, the external circuit of the power pin should be checked carefully. After ruling out the possibility of circuit failure, it indicates that there is a problem with the integrated circuit. When the DC operating voltage on the power pin is low, it is likely that there is a short circuit fault in the circuit inside the power pin of the integrated circuit.

(6) Some specialized integrated circuits have a fixed proportional relationship between the DC operating voltage of some pins and the operating voltage on the power pins, which is useful for checking faults without the standard voltage of each pin of the integrated circuit. For example, OTL power amplifier integrated circuit

The DC voltage of the signal output pin is equal to half of the DC voltage on the power pin; The DC voltage of the signal output pin of the OCL power amplifier integrated circuit is equal to 0V; The two signal output pins of the BTL power amplifier integrated circuit have equal DC voltage, which is equal to half of the DC voltage on the power pin.

(7) Among various integrated circuits, the DC voltage on the power pin is the highest, and this should be known even without any information.

(8) The DC working voltage of the whole machine is higher under no-load conditions than during operation, and the higher the voltage, the greater the internal resistance of the power supply. So, when measuring DC voltage, it should be done while the machine is in operation.