Hi,

  Updating JM4 firmware shouldn't be a difficult thing to do, but there are several points of potential difficulty that we at Line 6 cannot "control":

  1. The SD Card an end user has purchased/is using. It does need to be a Standard SD card less than 2 Gigabytes in size, formatted to FAT filesystem.

  2. The fw.bin file you grab from our server at http://www.line6.com/software/readeula.html?rid=2381 is the raw system firmware. If you have Anti-Virus actively scanning the download, this CAN cause corruption in the raw data, which in turn can cause a symptom like the one you've described.

  I'm willing to bet changing one of the two mentioned points above should take care of your issue. There is, of course the possibility of a hardware issue in the JM4, but before jumping to that conclusion, you should try again with the recommendations I've provided in mind.

  Let us know.

  Regards,

  L6Perry