Altera USB Blaster JTAG problem: Suddenly unable to connect to FPGA

--- Quote Start ---

Today, a second board has started to fail as the first one.

Whats going wrong? I've found several threads where people suggest to load 3.8V or 5V directly on the TDO pins for several seconds in order to blow up a protection. I've tried this with no success.

--- Quote End ---

Hi Eduardo.

Applying 3.8 to 5V on the TDO line sounds like a method of destroying the TDO.. I would definitly not due this.

What is the VCCIO of the bank with the JTAG lines. If it's 3.3 V, you may have enough overshoot that you are killing the FPGA pins due to overshoot/undershoot unless you have external clamp diodes installed.

I haven't see this issue, but I have seen issues when the VCC of the USB Blaster connector is too high. Check the Cyclone V handbook, and see if this is the issue.

I have also seen issues due to poor TCK termination on the board. I adjusted one of my USB blasters by switching the 10 ohm source termination resistor with a 33 ohm source termination resistor.

Pete