Typically when I see that error it is due to bad pickup rollers. Since you state the pickup assembly doesn't activate at all, and you've already replaced the dc controller board, then next in line is the pickup assembly. HP doesn't really troubleshoot per se - they have you describe the symptoms then they look it up in their service manual and work their way down the list of what parts to replace to (hopefully) fix the problem. You *should* be on the right track.