Hi Sam,
I can only find 1 reference to the error code tables for the LH76 chassis. All is states is Code 3..SOS. Tried to upload the service manual to the site for you but "file not supported". Suffice to say it will be a LT rail in pain, so it could be on the PSU or could be another board loading it down. My gut feeling is the PSU, but ah dinnae ken.