Acorn Risc PC 700 Troubleshooting Guide

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.

Acorn Risc PC 700. Source: Wikimedia Commons.

⚠️ 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