The method is...
1) To determine whether the chip is normal, see the block diagram of MAX232, use a multimeter to measure pin 2 and 6, as long as the voltage of pin 2 is between +8V ~ +9V, and pin 6 is between -8V~-9V, you can basically determine that the chip is good;
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2) When Rs232 does not send a signal, see the TX terminal voltage is a high level of Rs232, that is, between -8V and -9V, when the signal is sent, the data is changing, which indicates that the Rs232 port is good; This method also applies to measuring local serial ports.