Stratix III JTAG Failure

[Altera_Forum]

Hi All, 

 I have problem on Stratix III device on my Custom development board.   Device: Stratix III - EP3SL340  Download cable : Altera USB Blaster    We have provided two configuration option to configure the FPGA (JTAG & Passive serial). Only one device is connected with the JTAG interface.   We are frequently using JTAG & USB blaster interface to validate our designs. so far It was working nicely.   Suddenly the quartus Tool is not able to detect the device from the JTAG chain.    I just went through the JTAG troble shooter, It gives the information of possible failure in the JTAG interface signal,   Also I have noticed that TDI pin is almost shorting to GND.  It shows 2 Ohm between TDI to GND.    Whereas the other working board it was around 150 to 200 ohm.   This is the second board I am facing the same issue.  Is it the problem with the Stratix III device JTAG interface. Can anyone help me to findout the root cause for this trouble.   Best Regards, Kalidoss

[Altera_Forum]

Thanks but no hope for me :p

[Altera_Forum]

I had exactly the same thing and solved in the same way. 

Our JTAG was not working anymore while the board worked for more than a month. TDI was measuring 50 Ohm to ground.  We suspected an FPGA problem and no board problem. I disconnected the normal powersupply and I applied 5V to TDI from seperate power supply and ground to the ground of the board. This to "burn" the short in the FPGA... small change that it worked but as I could not use JTAG anyway it was no big loss if the FPGA would burn completely.   The resistance was increasing. After applying the voltage for a second it was 70 Ohms, applying again for 5 seconds it became 150 Ohms but still not working. After another 10 seconds it became 2 Ohms and I put the board aside because I thought the board was now completely defective.  However, after reading this thread I tried it again. TDI became 5k and I can program the JIC into the board.   FPGA was a Stratix III 3SL70F780C4N.  How can this happen? Is it a bad FPGA... or could short on TDI caused by electrostatic discharge?