JTAG in repair realm - Page 1
Forum section: electronics / repair

author: Samogon
author_rank: Frequent Contributor
timestamp: December 28, 2017, 07:05:34 am
content: I am wondering if it makes sense to go inti repair path of digital systems with microcontrollers and embeded systems all sorts of FPGA. Most of the modern equipment becomes highly integrated and leaves less space for DMM and scope probes to test.So here it comes JTAG and looks appealing to use it as repair/debuging tool.Could someone give advise where to start software/cables/adapters.PS Please do not suggest 10-20$k xjtag solution i believe it is nice but way out of my budget.Thank you

author: ataradov
author_rank: Super Contributor
timestamp: December 28, 2017, 07:37:46 am
content: How exactly do you plan to use JTAG for repair? The most you can do is a boundary scan, but without information about the board, it won't do you any good. You may be able to collect this information over time for a limited number of boards, but you will do the same with the knowledge for typical failures anyway.If you have time to spare, and some board to play with, you can start with a simple Arduino project to do the boundary scan.Other than this, most JTAG adapters will have some sort of a scripting tool. But again, you will get access to the pins, but without structured information about the board, this will be of a very limited value.

author: Rasz
author_rank: Super Contributor
timestamp: December 28, 2017, 08:01:12 am
content: JTAG is useless for repair of recent modern electronics (other than removing connector from liquid damaged macbook board haha).Only potential way to use it is acquiring (thru less than legit ways) manufacturers own diagnostic/service tools, or counting on clever people in Belarus/Russia/China to clone/reverse engineer one. This is how for example BMW canbus key clone tools are available on ebay.TLDR: Yes, there mostly do exist automagic tools that report "module X defective, signal X missing/outside set parameters", but they are used by the fab to bin/recycle straight on manufacturing line, or by certified technicians under NDA up the ass to replace whole modules without touching soldering iron.

author: Samogon
author_rank: Frequent Contributor
timestamp: December 28, 2017, 01:10:19 pm
content: Ah another fruitless idea.

author: mlefe
author_rank: Regular Contributor
timestamp: January 14, 2018, 03:42:36 pm
content: Guys, I'm also a beginner and I thought something along the same line...In my case, I'm repairing a board with BGA memory and I have no easy way to understand if that's fried or something else is going on. I was thinking about listening to the messages to see if I can pick that up: does it make sense?

author: Samogon
author_rank: Frequent Contributor
timestamp: January 14, 2018, 04:41:45 pm
content: Well, I purchased xlinx cable and will try to use it anyway just for fun if not for repair.Memory itself cant be connected. As I understand jtag is used on CPUs and micro controllers, and then you can scan other chips as a chain scan.So find CPU then probably you will need specific manufacturer connector and software to at least get boundary scan.

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 14, 2018, 05:58:41 pm
content: Quote from: Samogon on January 14, 2018, 04:41:45 pmYes, JTAG is proprietary, which is why they are useless to third party repair shops. (Hence Louis destroys them)