FCO KN15-AA-0002, TURBOchannel DMA Reads & Conflicted I/O Writes

This document, a Field Change Order (FCO), addresses a critical hardware issue affecting DEC3000 AXP Model 500/500S systems. The problem, which manifests as an indefinite system hang requiring a hard reset, stems from an interaction between TURBOchannel DMA reads and conflicted I/O writes, and is undetectable by software. The FCO is applicable only to systems exhibiting these symptoms and having system modules below revision "J05" (for D etch modules) or "J06" (for F etch modules).

The solution involves replacing the problematic system module with a new one of revision "J05" (D etch) or "J06" (F etch). Installation instructions detail the steps, including referencing the service manual, safely shutting down the system, disassembling components (cables, memory boards, TURBOchannel options), removing the old module, installing the new one, reassembling the system, and running power-up self-tests before rebooting. Electrostatic discharge (ESD) precautions are emphasized. The required parts include a specific system module and a Field Application Document. Activity related to this FCO must be reported on a LARS form.