Acorn System 3 Troubleshooting Guide
This guide gives diagnosis for the Acorn System 3 (1980). The System 3 is a Eurocard rack, so diagnose by card (as for the System 2) and add the floppy-disc subsystem. The CPU and cassette cards are the Acorn System 1 cards.[1]
Method
[edit | edit source]Reduce to a minimum (CPU + memory/BASIC + VDU) and confirm the machine boots BASIC; then add the FDC card and drive. A fault that appears with one card isolates to it or its slot. Confirm the backplane rails at an empty slot first.
No display / no boot
[edit | edit source]Use the Acorn System 2 Troubleshooting Guide for the CPU, memory and VDU cards: verify the 1 MHz clock and 6502, the BASIC ROM and RAM, and the MC6845/SAA5050 on the VDU card.
Floppy-disc faults
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| Disc not detected / no DOS prompt | FDC card, ribbon cable, or drive | Reseat the 8271 and the ribbon; check drive power; try a known-good drive |
| Reads own discs, not others | Head alignment | Align with a reference disc |
| Read/seek errors | Dirty head, worn belt, or media | Clean the head; check the belt; try known-good media |
| DOS will not load | DOS ROM or its select | Reseat the DOS ROM; verify the FDC card links |
The floppy controller is the Intel 8271; reseat it and verify the disc-side cable before condemning the card.[1]
6809 / FLEX systems
[edit | edit source]A System 3 fitted with the 6809 CPU card runs FLEX. If such a machine will not boot, confirm which CPU card is fitted and that the matching OS ROM/disc is present; the 6502 and 6809 cards are not interchangeable without the corresponding software.[1]
Backplane and connectors
[edit | edit source]A machine that works only when a card is pressed has a dirty or loose edge connector; clean the fingers and the backplane socket. Check the backplane power-input joints.
Common fault catalogue
[edit | edit source]- Dead, rails present — CPU card; apply the System 1 checks.
- Boots BASIC, no disc — FDC card (8271), ribbon, or drive.
- Read/seek errors — head cleaning/alignment or media.
- No display — VDU card or monitor.
- Intermittent when jostled — dirty edge connector or backplane joint.
Related pages
[edit | edit source]- Acorn System 3
- Acorn System 3 Maintenance Guide
- Acorn System 3 Capacitor Replacement Guide
- Acorn System 2 Troubleshooting Guide · Acorn System 1 Troubleshooting Guide
References
[edit | edit source]- ↑ 1.0 1.1 1.2 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.