I purchased my DT50 Head on August 2012. Received an email about my serial number qualified for tech bulletin 59 in April 2013 and I sent it to Line6 to do it.. The only thing wrong before the update was some severe hiss on some patches using the HD500 with it, as well as some slight noise and pops by itself, which the latest firmware seemed to mostly fix. Amp cam back about two weeks later and seemed fine. June 15th, it would not power on, found out the main fuse (5 amp) was blown. Bought a couple new fuses and tried it again. New fuse blew immediately on power up (tried it twice, blown both times). From my research, most people with this problem ended up having a new transformer installed to fix the problem (which I believe tech bulletin 59 was supposed to fix). Looks like it is off to be inspected again. I have had it for less than a year, hopefully the fix won't cost me. Thank goodness I have my Mesa dual rectifier as a backup still (which has never had an issue)
I'll put an update if I ever get one...
I have an update. Luckily an authorized repair facility was only 60 miles from my house, so I dropped it off and several weeks later it was fixed. The repairs were related to Technical Bulletin 059, and whatever part was installed during that had failed so Line 6 covered it under warranty. Awesome. If it wasn't covered, it would have been around $170 for the inspection parts and install. Here is a list of the parts and model numbers installed to make my DT50 operational again:
11-30-0044 Power Transformer
03-23-0101 Capacitor 100uF/160V
24-18-1625 Littlefuse 239 01.6, Series 239 1.6A/250V Slo blo
So in summary a new power transformer, capacitor and fuse is what was needed. I asked the tech is they found a reason why the original parts failed, no answer given. I'm just hoping the new hardware lasts.