The leading edge pulse disappeared. I am using the propagation delay of 3 nand gates fed to a 4th nand gate with the clock pulse to generate a pulse at the leading edge of the clock. A common technique that worked fine on a breadboard until I made it on a circuit board. Then logic states were ambiguous when circuit board was hand fabricated and the output was the clock pulse, not the small leading edge pulse I need. the scope shows that nand gate after the first gate produces an indeterminate state which is like a floating lead that stays high. I could use some advice on this. add additional gates, inverters (schmidt trigger) or look for something else. Thanks roylesq

 

You're not going to get much help without showing a circuit diagram.
What NAND gate? What is the chip number? What is the supply voltage?
What pins are connected to what pins? What pins are not connected?
Sometimes a photograph of your setup can actually reveal silly mistakes that written words do not convey.

 

sorry, I am new at this. this was my first post.
5 volt supply for 7400 (quad nand). I dont have diagram on the computer, the diagrams are hand drawn. there are no unconnected pins, 14 + 7 - 1, 2 and 9 are clock pulse 3-4-5 are tied 6-13-12 are tied 11-10 are tied. 8 should be the output with neg pulse at leading edge of clock pulse. clock pulse is 60 hz generated from op amp using ac supply to generate square wave between .2 and 5 v. I am not at the workbench, but will try to use photos when I can.

 

Then I say you have bad wiring on your circuit board. You will have to post photographs of both sides of your board.

 

Well, I checked but I am obviously missing something. Thanks. I will re-make it and see if that works.

 

Well, I checked but I am obviously missing something. Thanks. I will re-make it and see if that works.

No. Don't redo the board.
How would you know what you did wrong?
How do you know that you wouldn't repeat the same mistake?
Find out what you did wrong with what you have.
That way you learn from your mistakes.

I bet you do not have GND connected to pin-7.

 

I think I do, but i will check. I tested for GND and +5. the waveform for successive gates looks like grass, so it appears that there is rapid switching to the high state even though the signal should be low at that time (60 hz ; 8 ms high, 8 ms low) but i cannot discern discreet pulses even at the scope's fastest time. The 5 v supply does not look solid at the chip (7400) although it looks solid everywhere else on the board. (line looks thick during 1/2 the cycle : 8 ms intervals) I have replaced the chip, of course, a couple of times.

The mystery is that it worked well on the breadboard. perhaps there is overflow solder on the board. I will get my magnifier out and look more closely and check connections again. It has been many years since I have done fabrication, so my skills are not so up to date. thanks for your support.