I am looking to duplicate a board, but i came across this chip which apparently comes in either 3 or 10 pF Input Capacitance, 50, 60 or 80 MHz, and different Max Propagation Delay 15ns, 26ns and 30ns. How can i figure out which one i need?

 

TI makes a 54HC74 (military) and a 74HC74 (consumer). Neither one will operate at 50MHz.

 

We would not know until you tell us the application and the requirements of the application.
I am going to make a guess that any one will do.

What is the frequency of the signal clocking the HC74?

 

I am looking to duplicate a board, but i came across this chip which apparently comes in either 3 or 10 pF Input Capacitance, 50, 60 or 80 MHz, and different Max Propagation Delay 15ns, 26ns and 30ns. How can i figure out which one i need?

I've never heard of digital IC's being segregated by input capacitance for any reason. I'm also quite sure that no chip from the 74HC family will operate at those frequencies. You can check the ordering information in the datasheet to see what the differences are, but they are mostly mechanical packaging and temperature over which the specification are guaranteed to some confidence level.

 

Since you are "looking to duplicate a board" you must have an idea as to what you want it to do. Thus you should be able to know what frequencies will be present, and that should give you a good idea as to which IC version to select.
To provide enough information for others to offer better than random guesses you need to provide more context, such as a picture covering more board area, and a description of the function of the board. If you are unable to do that, why are you wanting to make a copy????

 

It Is a fiber optic communication board

Since you are "looking to duplicate a board" you must have an idea as to what you want it to do. Thus you should be able to know what frequencies will be present, and that should give you a good idea as to which IC version to select.
To provide enough information for others to offer better than random guesses you need to provide more context, such as a picture covering more board area, and a description of the function of the board. If you are unable to do that, why are you wanting to make a copy????

 

It Is a fiber optic communication board

Commercial boards usually have protections (markings) to prevent illegal duplication.

 

Duplicating that board will be a very "big deal" at the least. It is at least a double sided board, quite probably a multi-layered board, with a whole lot of digital logic parts. In addition, U17 and the device to it's left in the picture, with the white covers, are probably programmable devices that may be a serious challenge to duplicate. So unless you have access to a great deal of expertise aside from this site I do not see creating a copy as a possibility.

 

This is a 25 year old part that no longer is manufactured, for obsolete equipment for personal use...

I have already successfully programmed duplicate proms etc so i am not worried about that, it is double sided with components on one side, i am going to give it my best try and things i post on here are last few things i need help on and that’s why i do so. You guys are great & i appreciate all your guys help

Duplicating that board will be a very "big deal" at the least. It is at least a double sided board, quite probably a multi-layered board, with a whole lot of digital logic parts. In addition, U17 and the device to it's left in the picture, with the white covers, are probably programmable devices that may be a serious challenge to duplicate. So unless you have access to a great deal of expertise aside from this site I do not see creating a copy as a possibility.

 

I am looking to duplicate a board, but i came across this chip which apparently comes in either 3 or 10 pF Input Capacitance, 50, 60 or 80 MHz, and different Max Propagation Delay 15ns, 26ns and 30ns. How can i figure out which one i need?

Apparently?
It would be simpler if you post the datasheet you have been reading.

Or is it a video in Youtube?

 

4 layers minimum. The internal power planes are pulled back 0.050" from the edges.

Photo of the bottom side?

ak

 

it is double sided

All over the board are capacitor from power to ground. C14 for example. On the other side of the board, are there power and ground traces to each of these or do they connect to a power and ground plane? Trying to know if it is a 4 layer board.

 

see attached

4 layers minimum. The internal power planes are pulled back 0.050" from the edges.

Photo of the bottom side?

ak

 

Looks like a 4-layer board with mostly orthogonal routing.

ak