Editing Acorn Risc PC 700 Troubleshooting Guide

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[[File:Acorn Risc PC 700 (photo).jpg|thumb|right|300px|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 [[Acorn Risc PC 600 Troubleshooting Guide|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.<ref name="trm">[[Acorn Risc PC Technical Reference Manual]] (Issue 1, September 1994; part 0497,057), Acorn Computers &mdash; hosted on this wiki. Source for the Power On Self Test and fault/status codes, the on-board fuses FS1 (2 A) and FS2 (800 mA), the NiMH battery, the IOMD/VIDC20/FDC37C665 architecture and the engineering drawings. The TRM documents the original 0197,000 board; the 700's 1208,000 board is a revision.</ref>

== ⚠️ 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).<ref name="trm" />

'''Normal sequence:''' '''purple''' (brief ROM/RAM tests, then IOMD and VIDC20 init and test &mdash; 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).

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{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''POST fault bits (bits 9&ndash;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 &mdash; 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 &mdash; 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.<ref name="trm" />

== Diagnostic flow ==

# '''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.<ref name="trm" />
# '''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.
# '''Red screen + LED code''': decode the 8-hex code (table above).
# '''No display''': try a known-good monitor; check the VGA connector and the video ID pin; verify VIDC20.
# '''Won't start with a second CPU/PC card''': retest with only the primary ARM710 card, reseated.

== Symptom table ==

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{| class="wikitable styled-table" style="width:100%; text-align:left;"
! 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 &mdash; 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 &mdash; 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]] &mdash; the near-identical 600 procedure
* [[Acorn Risc PC Technical Reference Manual]] · [[Capacitor Failure Symptoms]]

== References ==

<references />

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