[bnmand]

When you replaced the HD did you install the latest firmware? Old firmware could be a problem if it's spitting out error codes for no reason.

Other than that all I can think of is that maybe something that isn't expected to break down probably has due to the age of the machine (hence why it's not mentioned in the SM). I'd check near the parts you replaced to see if anything appears to be damaged or worn out.

I'd check to make sure that the copier recognises that the front door is open (if that's possible. May be somewhere under I/O menu in Service Mode).