Acorn Risc PC 700 Troubleshooting Guide

Acorn Risc PC 700. Source: Wikimedia Commons.

This guide gives diagnosis for the Acorn Risc PC 700 (ARM710, board 1208,000). The Risc PC 700 shares its diagnostics with the Risc PC 600: the same Power On Self Test (POST), the same IOMD/VIDC20/FDC37C665 chipset, the same on-board fuses, and the same surface-mount-electrolyte failure mode. The differences are the 40 MHz ARM710 CPU card and RISC OS 3.60. The POST and parts/electrical data are in the Acorn Risc PC Technical Reference Manual, which also holds the circuit diagrams.

⚠️ Mains warning

The Risc PC 700 has a fan-cooled mains PSU in the base slice. Disconnect the mains lead before removing the cover; the PSU primary side is at mains potential and the module should not be opened unless you are competent with mains switch-mode supplies (discharge the primary bulk capacitor first).

Power On Self Test (POST)

The 700 runs the same POST as the 600. Progress is shown by the screen colour, and a failure is signalled on screen (red) and by the floppy-disc LED flashing an 8-digit hexadecimal fault code (long flash = 1, short flash = 0).

Normal sequence: purple (brief ROM/RAM tests, then IOMD and VIDC20 init and test — a crash here indicates a major I/O fault) → screen mode set from the video ID[0] pin (VGA or 15 kHz TV mode; no stable display means a monitor, video or fundamental fault) → blue (extensive memory test, then video and sound tests) → purple (ARM ID read; needs good RAM) → green (pass; RISC OS starts and shows a black screen with the memory-size message) or red (fail; floppy LED flashes the code).

POST fault bits (bits 9–31 indicate faults)

Code	Meaning	First-look
00000200	ROM failed checksum	Reseat/replace the RISC OS 3.60 ROMs
00001000	IOC register test failed	IOMD or its bus
00004000	VIDC (Virq) timing failed	VIDC20 or its clock/interrupt path
00008000	Sound (Sirq) timing failed	VIDC20 16-bit sound path
00010000	CMOS unreadable	I²C path to CMOS/RTC; battery circuitry
00020000	RAM control line failure	Classic leaked-electrolyte symptom — recap and repair corroded RAM-control tracks; reseat SIMMs
00040000	Long RAM test failure	Faulty SIMM; substitute

Informational status bits include 00000040 (integrated I/O fitted), 00000080 (VRAM present — standard on the 700) and 00000100 (CMOS checksum error). A POST interface box on the parallel port shows the tests and a PASS/FAIL bitmap on an LCD.

Diagnostic flow

1. Completely dead: check the mains-plug fuse; with the lid open, confirm the PSU rails and fan; check on-board fuses FS1 (2 A) and FS2 (800 mA) for continuity.
2. Crashes early / RAM-control fault (00020000): inspect the board for leaked surface-mount electrolyte and corroded RAM-control tracks; recap and clean; reseat SIMMs and the VRAM.
3. Red screen + LED code: decode the 8-hex code (table above).
4. No display: try a known-good monitor; check the VGA connector and the video ID pin; verify VIDC20.
5. Won't start with a second CPU/PC card: retest with only the primary ARM710 card, reseated.

Symptom table

Symptom	Probable cause	Action
Completely dead	Mains fuse, PSU, or on-board fuse	Check plug fuse, PSU rails/fan, FS1/FS2
Crashes early (purple) / RAM-control fault	Leaked electrolyte or bad SIMM	Recap and clean; reseat/substitute SIMMs
Red screen, floppy LED flashing	POST fault — read the code	Decode the LED code
No stable display	Monitor/cable, video ID pin, VIDC20	Try another monitor; check VGA; verify VIDC20
Lost configuration / wrong clock	Flat or leaked NiMH battery (BT1)	Clean, repair tracks, replace cell
No / distorted sound (00008000)	VIDC20 16-bit sound path or leaked caps	Recap; check the sound path
Hard disc not found	IDE cable/power or dead drive	Reseat the cable; replace the drive
One subsystem dead, rails present	Blown on-board fuse	Check FS1/FS2

Always suspect leaked electrolyte

As on the 600 and the Acorn Archimedes A5000, intermittent and progressive Risc PC faults are frequently leaked surface-mount electrolytic capacitors rather than a failed IC, and the POST "RAM control line failure" code points straight at corroded RAM-control tracks. Inspect under magnification and recap before deeper diagnosis — see Acorn Risc PC 700 Capacitor Guide.

Storage and ports

• Hard disc not detected: check the 40-way IDE cable and drive power. RISC OS 3.60 supports discs larger than 512 MB.
• Floppy: clean the head and try a known-good disc before suspecting the FDC37C665.
• Serial/parallel: handled by the FDC37C665.
• Expansion: clean the podule backplane and network-card contacts.

Related pages

• Acorn Risc PC 700
• Acorn Risc PC 700 Maintenance Guide
• Acorn Risc PC 700 Capacitor Guide
• Acorn Risc PC 600 Troubleshooting Guide — the near-identical 600 procedure
• Acorn Risc PC Technical Reference Manual · Capacitor Failure Symptoms