SN74LS244: SN74LS244NSR

Normal output signalWhat causes this kind of thing?

Please show a schematic, and a single screenshot of an oscilloscope trace with both input and output signals.

This is normal

This is an anomaly in the output

After replacing the other batches of materials, the problem was solved, but these 2 batches of materials were ordered directly from TI, what is the reason for this anomaly?

Where is the input signal in these waveforms?

The test is 3PIN input and 17PIN output, and the resulting waveform is obtained. The performance on the product is that key A also responds when key A is pressed.

This is the circuit diagram

The performance on the product is that key A also responds when key B is pressed.

You will not get an output signal on pin 17 because it is an input pin.

In the oscilloscope screenshots, which waveform is the input, and which waveform is the output?

This is the waveform of the input signal

This is the waveform of the output signal

3PIN IN 17PIN OUTPUT Sorry for the error described earlier

Dear Clemens Ladisch Please also help with the analysis and look forward to replying as soon as possible. Thank you!

I do not have an explanation of this behaviour?

Where exactly did you measure these? Direct at the pins of the '244, or at the other side of the resistors?

Hi Clemens Ladisch  This chip is soldered to the PCB board, and when the test is tested, it is found that the B key will also respond when the key A is pressed, and the last test is directly on the PCB board, and the waveform diagram is shown above. I hope to get your help to analyze the reasons for this situation.thank you.

It is a waveform obtained from the measurement of the energizing work on the PCB board, if you need any other explanations, please feel free to tell me, thank you!

Direct at the pins of the '244

Hi Tony,

Try measuring at the other side of the resistors. Could I get a better look at the board/schematic?

Best,

Malcolm

Hi Malcolm Glad to get your reply, is there a circuit diagram you can see above?Do I need to do other tests and feedback for you to analyze further?Please tell me more about what I need to do?Thank you!

I see the schematic above. Could I see the actual physical board?

Best,

Malcolm

Hi Malcolm  This is the PCB board, and the position of U6 corresponds to the chip 244. Please feel free to let me know if you need any other information from my side, thank you!

Tony,

Could you provide a better picture of the board? I can't really discern anything from the picture you provided.

Also I would like to ask about this:

Tony zeng said:

it is found that the B key will also respond when the key A is pressed

Are you sure that there is not a short somewhere on the board? That would probably explain the issue.

Best,

Malcolm

Hi Malcom

First of all, thank you for your reply。

You can take a look at what I described earlier, when I replaced other batches of 244 chips on the PCB board with abnormalities, the problem was solved, and it was found that the problem followed the chips. But these 2 batches of chips are purchased from TI, and the production date codes are 2134 (with abnormality) and 2138 (without abnormality) The production time is very close, this is very confusing?