Maintenance? HDD: file defragmentation/file-directory repair/archiving files (to maintain less than 85% fullth [a technical term]). Break-and-make of all connector-socket junctions. Cable-integrity check, especially the HDD cables where they exit from the fold-up part of the chassis if you have drives on the floor or SCSI HBAs. Does the 80/50 adapter have high-byte termination and provide termination power? Why not consider installation of a Wide SCSI HBA and 68/80 adapter so as not to strangle the Seagate's performance? Are you using either EDO or FPM RAM, but not both, inserted in A6/B6 and A5/B5 slots?

MLB inspection? Nothing burnt, missing or vaporized/leaking?

Full reset of the MLB? All power removed after measuring the PRAM battery's voltage in circuit as 3.3V or more. Leave unpowered for at least 10min. Use the CUDA for not less than 40sec after reassembly but before restoration of mains voltage, closure and powering-up.

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