I've done a jtag b4 with a pansat3500SD i'm trying to do it with a pansat3500s but there is no 20 pin holder...my question is do i have to buy a 20 pin holder in order to jtag or is there another way to do it?
If there isn't one on your board you might have to purchase a header and solder it on. Sometimes, you can get solderless headers but they have to speced to your specific receiver (because of height differences between the hood and your motherboard).
you need a JTAG cable as well as software for your computer to do a JTAG. There are many manuals on various DSS sites that tell you how to JTAG.
You need to JTAG when you download (to your receiver) the wrong bin or when something goes wrong with your download and your receiver won't boot.
Not all receiver can be JTAGed (or easily JTAGed). For instance, Pansats usu. provide a method to JTAG but Viewsat does not. You have to check about other receivers.