VB.NET how to replace byte chrs that can't be displayed with "?"

I have a network packet that has some ascii text in it as well as some bytes that cant be displayed in the immediate window or console

what i need is a function that can take this byte string & replace any characters that can't be displayed with "?"

for example chr(0) doesn't show up as anything, there are also other characters that don't show up when written out to the console... as if they don't have a symbol/letter/number/etc associated with it

i guess the function needs to replace anything that doesn't have a chr/num/symbol associated with it