Tool/software:
During production, an abnormal phenomenon occurred on a batch of motherboards after power-up. The same batch of motherboards used two different printed OP07 chips, and the problematic ones were from the same batch of OP07. The principle behind this is as follows:
Figure 1 Schematic Diagram
1.The defective chips were identified as part of the same incoming batch, marked with the silkscreen code "52M" (as shown below).
Figure 2
2.In this circuit, the OP07 chip uses a total of 5 pins, with pins 1, 5, and 8 left floating: Pin 4: Power supply (-15V) Pin 7: Power supply (+15V) Pin 3: Ground These three pins show normal voltage levels. However, pins 2 and 6 exhibit abnormalities. The waveform diagrams for pins 2 and 6 of the OP07 chip with the "52M" marking are shown below:
Figure 3 Abnormal waveform at Pin 2 of the op-amp
Figure 4 Abnormal waveform at Pin 6 of the op-amp
3.After replacing with an OP07 marked "52K," all voltages returned to normal. The silkscreen of the "52K" OP07 is shown below:
Figure 5 Silkscreen Comparison
4.The normal waveform between Pin 2 (inverting input) and Pin 6 (output) of the OP07 in the same circuit is as follows:
Figure 7 Normal waveform at Pin 2 of the op-amp
Figure 8 Normal waveform at Pin 6 of the op-amp
The OP07 chips from the same batch with markings "52M" and "52K" exhibit differences, which caused the abnormal behavior in this circuit.
