Circuit Debugging Tips

Possible Problems related to Buffer Chips

In most cases, if the digital output is not as expected, we should check the buffer chip. Here are some tips.

A shorted buffer chip

Due to various kinds of reasons, your circuit produces a shorted buffer chip for you with respect.

How to check

If a chip is shorted, in 90% of the cases, some pins are connected to the ground. Use the beep mode of the multimeter, one end connecting the ground and sliding the other end across each pin of the chip. If you hear beeps when you touch pins that should not be connected to the ground, you can pull out the chip and do a dry check. If the beep remains, you have a broken chip.

A defective buffer chip

Since the output of the buffer chip is in range 0~3.3V, if you connect one end of an LED to 5V and the other end to the buffer chip, the LED is supposed to be turned off if the buffer chip produces a logic high (3.3V). However, a defective buffer chip may not able to produce as high as 3.3V, but 2.8V, even though the input is logic high, 2.8V is still low enough to lit up an LED.

How to check

Check the to-ground voltage of both side of the LED, see whether the voltages are reasonable.