I work in a company which develops devices that need to withstand harsh environmental conditions, shocks, radiations, vibrations and whatever. Really, too many to count.
In one of those devices is a small existing board which basically takes RS-232 and RS-422 signals, runs them through some kind of protection, and transfers them forward.
Here are the two types of circuits:
World - the signal comes from the outside (or goes outside).
Internal - the signal connects internally to a connector in the device. All the internal signals are connected to some industrial board that acts as some controller.
In the board, the resistors are on one side and they are SMD. The diodes and capacitors are on the other side and are TH. The diodes used in the RS-232 (and perhaps also RS-422) protection circuits are the 1N4744A.
To be honest, We're not sure what these protection circuits do, since it was designed long ago and the engineer that designed it left the company. Perhaps lightning protection? It would be great if you could tell me what those circuits could be for.
We want to produce more of these boards but the TH components being TH is giving us problems. I know this isn't a lot of information, but is it possible for you to know if the diodes and capacitors can be SMD instead of TH?