3.27 V instead 3.3 is good. Can be even bigger difference.
Laser pcb is connected through printer control pcb, so really PCI-LVDS/ARCNET PCB has connection with ARCNET hub on printer control pcb. Just do not see printer board itself.
Try from printer control pcb disconnect ARCNET cables, which goes to laser control pcb. Then run self check and see results. Laser pcb will be - ( because disconnected ) . For you most important is connection status with printer control pcb.
If even then printer control pcb is "- "then try connect ARCNET cables to other pair on printer control pcb. Then repeat self test again. Do the same, when connected to third pair. ARCNET cables can connect, or disconnect when minilab is powered. If no connection then probably printer pcb is really faulty. To be 100% sure can try test your board on some QSS32, or QSS34 series minilab ( can connect and run self test there ) .
On LPS-24PRO can be used J390947 or J391254 removed from disassembled QSS32, or QSS34. Just need to make software upgrade from HD ( only for printer control pcb ) and from backup load printer data.