D6 Error code need help to resolve

Our J26 machine is down for error D6 (under voltage-drive) below is what I did to date w/o any success so asking for help. 1. Removed PD board found fuse F4 had failed, visual inspection of board all looks good, replaced F4 fuse reinstalled ran test. Error D6 again. 2. Checked PD board found F3 fuse had failed. Replaced F3 ran test machine failed D6 again. 3. Removed aluminum cover in front on the right-side found 2 more boards one I believe is the SR drive board and the other Sr board. 4. With all covers off and cover limit switch engaged I powered up the machine I noticed there are 4lights on the PD board and lights on the Sr board. I ran another cycle and same fail for D6. On the PD board a saw some red lights change state when the machine alarmed out hoping this is helpful for troubleshooting.