Why USB-Blaster II does not work after closing the Quartus® Programmer Hardware Setup window? - Why USB-Blaster II does not work after closing the Quartus® Programmer Hardware Setup window? Description When using Quartus® Prime Standard Edition to program a MAX® 10 FPGA device with a USB-Blaster II, changing the Hardware Setup frequency from the default 24 MHz to 16 MHz and then closing the Hardware Setup window with the Close button may cause the USB-Blaster II to stop functioning. Resolution Here are some practical solutions you can try to resolve the issue: 1. Restart the JTAG server. jtagserver --stop jtagserver --start 2. Unplug and replug the USB-Blaster II. 3. Kill lingering processes such as the JTAG server or Quartus Programmer process. jtagserver.exe quartus_pgm.exe 4. Change the clock frequency of the USB-Blaster II download cable to lower frequency like 16Mz and 6Mz. Related KDB: How do I change the clock frequency of the USB-Blaster II download cable? | Altera Community - 342304 5. Avoid USB conflicts by disconnecting other USB serial devices, especially FTDI or USB-UART adapters, and avoid opening COM ports or serial terminal applications while programming. 6. Try a different USB port and connect the USB-Blaster II directly to the PC instead of through a USB hub. 7. Reinstall the driver from the Quartus installation folder or try an older or known-stable driver version. 8. Avoid mixing drivers from multiple Quartus versions. 9. If a USB hub is required, avoid poor-quality or legacy USB 1.0 hubs. 10. If a clone USB-Blaster is being used, replace it with a known-good cable. 11. If none of the above steps recover the problem, reboot the system. Possible root causes: 1. JTAG server gets stuck and keeps the USB-Blaster II claimed. The device can appear normal in the operating system but remain inaccessible from Quartus Programmer. Restarting Quartus alone often does not recover the cable. Fix: jtagserver --stop jtagserver --start Or kill the process via Task Manager. 2. USB or driver conflicts with other devices. Conflicts with other devices, especially FTDI or USB-UART adapters, can break the USB-Blaster II mid-session. Opening a serial terminal can trigger the failure. This behavior is reported more often on Windows 64-bit systems. Fix: Disconnect other USB serial devices. Avoid opening COM ports or serial terminal applications while programming. Try a different USB port with a direct connection instead of a USB hub. 3. Driver bugs or Quartus version mismatches. Driver bugs or Quartus version mismatches can prevent Quartus Programmer from detecting the cable. Known bad driver versions or incompatible Quartus releases can cause the Programmer to lose the cable or prevent the standalone Programmer from detecting it. Fix: Reinstall the driver from the Quartus installation folder. Try an older or known-stable driver version. Avoid mixing drivers from multiple Quartus versions. 4. USB hub or signal quality problems. USB hub or signal quality problems can cause the USB-Blaster II to disappear after use. This is reported more often with poor-quality hubs or legacy USB 1.0 hubs. Fix: Plug the USB-Blaster II directly into the PC. Avoid poor-quality or legacy USB 1.0 hubs. 5. Clone USB-Blaster hardware. Clone USB-Blaster hardware can be unstable due to timing issues, firmware quirks, or driver incompatibilities. Fix: Replace the clone USB-Blaster with a known-good cable. 6. Closing Quartus Programmer leaves the cable in a bad state. Closing Quartus Programmer can leave the JTAG server running. It can leave the device handle locked. It can trigger USB re-enumeration issues on the USB stack. When Quartus Programmer is reopened, it may not be able to reattach to the already claimed cable. Fix: Unplug and replug the USB-Blaster II. Kill lingering JTAG server or Quartus Programmer processes. Reboot the system if the cable is still not detected. Custom Fields values: ['Download Cable II'] Troubleshooting QS-91850 novalue ['FPGA Dev Tools Quartus® Prime Software Standard'] No plan to fix 19.1 ['MAX® 10 FPGAs']