Acorn System 4 Troubleshooting Guide
This guide gives diagnosis for the Acorn System 4 (1980), a 14-slot double-height Eurocard rack with two floppy drives. Diagnose by card as for the System 3, with attention to the larger backplane and the integral mains power supply.[1]
⚠️ Mains warning
[edit | edit source]The cased System 4 has a mains PSU. Disconnect the mains lead before opening; the PSU primary side is at mains potential.
First: power and backplane
[edit | edit source]- With the mains off, then on (lid open, take care), confirm the backplane rails (+5 V and any ±12 V) at an empty slot. A dead rail points to the PSU or the backplane power wiring.
- On a 14-slot rack, reduce to a minimum (CPU + RAM + VDU) and add cards back one at a time to isolate a faulty card or a shorted card pulling a rail down.
Card-level diagnosis
[edit | edit source]Use the System 1/2/3 guides for the individual cards:
- CPU card — Acorn System 1 Troubleshooting Guide (1 MHz clock, 6502, ROM, RAM).
- VDU / memory cards — Acorn System 2 Troubleshooting Guide.
- Floppy subsystem — Acorn System 3 Troubleshooting Guide (Intel 8271, ribbon, drives, alignment).
Econet file-server faults
[edit | edit source]A System 4 used as an Econet server depends on the Econet card and the network: check the Econet card seating, the clock/termination on the network, and the file-server ROM. A server that boots locally but is invisible on the network points to the Econet card or the cabling rather than the CPU.[1]
Backplane
[edit | edit source]With many slots, a single shorted card or a dirty contact can take down the whole rack. Pull all cards and add them back; clean edge fingers and backplane sockets; inspect the backplane power-input joints for cracks.
Common fault catalogue
[edit | edit source]- Dead, no rails — mains PSU or backplane power wiring.
- Dead, rails present — CPU card; apply the System 1 checks.
- A rail collapses with one card fitted — shorted card; isolate by substitution.
- No disc — FDC (8271), ribbon or drive.
- Not visible on Econet — Econet card or network cabling/termination.
- Intermittent when jostled — dirty edge connector or backplane joint.
Related pages
[edit | edit source]- Acorn System 4
- Acorn System 4 Maintenance Guide
- Acorn System 4 Capacitor Replacement Guide
- Acorn System 3 Troubleshooting Guide · Acorn System 1 Troubleshooting Guide
References
[edit | edit source]- ↑ 1.0 1.1 Acorn System Catalogue and Acorn System 1 Technical Manual, Acorn Computers — hosted on this wiki. Source for the Eurocard set, the Intel 8271 floppy controller and the shared card detail.