Editing Sinclair ZX Spectrum +2 Troubleshooting Guide (section)

=== The IC numbering trap ===

Most Spectrum diagnostic tools report faults using '''48K Spectrum''' IC numbers. On the +2 board the mapping is:<ref name="tyne" />

{| class="wikitable styled-table" style="width:80%; text-align:left;"
|+'''+2 RAM IC numbering vs 48K Spectrum'''
! +2 board !! Equivalent 48K number !! Notes
|-
| IC17–IC24 || IC15–IC22 || Upper set, same order
|-
| IC25–IC32 || IC13–IC6 || Lower set — '''note the reverse order'''
|}

So a tool reporting "IC8 and IC13 faulty" means '''IC30 and IC25''' on a +2; a report of "D4 on the lower RAM" corresponds to '''IC28'''.<ref name="tyne" />