Editing Psion Series 3a Troubleshooting Guide

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[[File:Psion Series 3a open.jpg|thumb|420px|Diagnose in this order: batteries and the battery lead, then the button bar ribbon, then the screen ribbon, then the hinges. Four faults account for almost every dead Series 3.]]

Fault-finding for the '''[[Psion Series 3a]]'''. Most of it applies to the [[Psion Series 3]], [[Psion Series 3c]] and [[Psion Series 3mx]] as well; model-specific differences are called out.

Psion published a detailed '''SIBO Hardware Reference''' describing the architecture, the supply rails and the power states, which makes systematic diagnosis possible on these machines.<ref name="sibo">Psion PLC, ''SIBO Hardware Reference'', version 2.10, 3 February 1995, in the [https://doc.psion.info/books/the-psion-sibo-software-development-kit/page/hardware-reference Psion Documentation Project]. Source for the SIBO architecture, ASIC1/ASIC2/ASIC9, memory decoding, interrupt allocation, the watchdog, the NMI sources, the four power states and every supply rail described here.</ref>

== ⚠️ Before you start ==

* '''Back up first if the machine works at all.''' Diagnosis involves removing batteries, and RAM contents do not survive.
* '''Open both SSD doors before lifting the mainboard.''' On a [[Psion Series 3mx|3mx]] this is not optional — see below.<ref name="rc3mx">Richard Zealley, [https://www.retrocoding.uk/psion-3mx-ssd-microswitch-repair/ "Psion Series 3mx SSD door microswitch repair"], Retro Coding, 25 May 2020. Source for the SSD door microswitch failure, its cause, the symptom, and the fact that both switches must be repaired.</ref>
* Anti-static precautions throughout.

== Step 1: the four usual suspects ==

# '''Batteries.''' Fit known-good alkaline AAs and a fresh CR1620. Check the AAs under load, not just open-circuit.
# '''The battery lead.''' See below — this is the single most under-diagnosed Series 3 fault.
# '''The screen ribbon.''' Vertical lines on the display mean the cable, not the LCD.
# '''The hinges.''' A crooked back edge or a button bar that flexes out means a broken hidden hinge.<ref name="mackay">David MacKay, [http://www.inference.org.uk/mackay/psion/psion9.html "Psion 3a Hinge breakages"]. Source for the hinge locations, failure modes and symptoms.</ref>

== Step 2: understand the power states ==

A SIBO machine has '''four''' power states, and knowing which one it is stuck in narrows the fault fast.<ref name="sibo" />

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''SIBO power states'''<ref name="sibo" />
! State !! What is powered !! What it means
|-
| '''Standby''' || Main oscillator and processor '''shut down'''; ASIC9 and all memory powered; the real-time clock running || The normal "off" state. Data is retained.
|-
| '''Backup''' || As standby, but '''Vcc1 comes from the backup cell''' and switching to operating is '''inhibited''' || The main cells have failed or are absent. '''A machine in backup state will refuse to switch on''' — that is by design, not a fault.
|-
| '''Idle''' || Processor powered, oscillator running, '''processor clock stopped''' || Waiting for an interrupt. The bus is quiet apart from screen refresh.
|-
| '''Operating''' || Everything running || Normal use.
|}

'''A machine that will not switch on with good-looking batteries is very often sitting in the backup state''' because the main supply is not actually reaching the board — which brings you straight back to the battery lead.

== Step 3: the supply rails ==

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''SIBO supply rails and their failure symptoms'''<ref name="sibo" />
! Rail !! Function !! Symptom when missing or wrong
|-
| '''Vcc1''' || ASIC9 and all memory. Present in every state. 3.3 V nominal on ASIC9 machines || Nothing works, and data is lost. Present-when-off but absent-when-on means the main converter has failed.
|-
| '''Vcc2''' || The processor and the expansion port. 5 V, off in standby || Machine appears dead but retains data — it never leaves standby.
|-
| '''Vcc3''' || LCD module and display drivers || Blank display although the machine otherwise runs and beeps.
|-
| '''Vee1''' || '''LCD bias — the contrast rail.''' Negative, from a flyback converter, '''set by a DAC in software''' || No usable contrast at any software setting. Note there is '''no contrast potentiometer''' on these machines — if the software control does nothing, the rail has failed.
|-
| '''Vcc5''' || 5 V to the external SSD slots || SSD packs not recognised at all.
|-
| '''Vh''' || '''+16 V Flash programming voltage''' to the SSD slots || '''Flash SSDs read but cannot be written or formatted.''' Reads do not use this rail.
|}

That last row is the cleanest diagnostic split in the whole machine: '''a Flash pack that reads fine but will not format points at the Vh converter, not at the pack.'''

== Symptom table ==

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Psion Series 3a — fault symptoms'''
! Symptom !! Likely cause !! Action
|-
| '''Eats batteries at a phenomenal rate''' || '''The battery lead.''' The lead between the mainboard and the battery contacts is twisted every time the lid opens; the wires fatigue and short together || Remove the screws behind the batteries and '''re-seat the two-pin connector''' — often a permanent cure. If the wires are damaged, replace them.<ref name="faq">Psion Series 3/3a community FAQ material and the comp.sys.psion newsgroup archives. Source for the "dreaded battery lead problem" and its fix, the backup-cell contact shim, and the button-bar ribbon reseating trick.</ref>
|-
| '''Appears to lose the battery connection intermittently''' || Same fault, earlier stage || As above.<ref name="faq" />
|-
| '''Will not switch on at all''' || Machine held in the '''backup state''' because the main supply is not reaching the board; flat cells; battery lead || Confirm the AAs are good under load, then go to the battery lead.
|-
| '''Vertical lines across the display''' || '''Deterioration of the screen ribbon cable''' running between the keyboard half and the screen || Replace the cable, or fit a donor lid. See [[Psion Series 3a Hinge Repair]] for the separation procedure.<ref name="wp3">[https://en.wikipedia.org/wiki/Psion_Series_3 "Psion Series 3"], Wikipedia. Source for the three documented clamshell problems: hinge breakage, button-bar failure and screen-cable deterioration producing vertical lines.</ref>
|-
| '''Display blank, machine otherwise alive''' || Contrast set out of range, or Vcc3/Vee1 failure || Adjust contrast in software first. Contrast is a '''software-controlled DAC''', so there is no wheel to turn.<ref name="sibo" />
|-
| '''Button bar does nothing''' || Its ribbon has come adrift from the lower PCB, usually after an impact || '''Push the ribbon back into its connector with a paperclip, with the lid half closed.'''<ref name="faq" />
|-
| '''Back edge looks crooked when opening; button bar flexes out''' || '''Broken hidden hinge nipple''' || See [[Psion Series 3a Hinge Repair]].<ref name="mackay" />
|-
| '''Lid loose or detached on one side''' || '''Visible hinge sheared''' at the 8 mm neck, from over-opening || Epoxy repair or donor lid.<ref name="mackay" />
|-
| '''Backup battery reported flat but measures fine''' || Contact pressure || A '''small piece of paper between the cell and the top contact''' is the documented fix.<ref name="faq" />
|-
| '''SSDs not recognised in either slot — "not ready"''' || '''On a 3mx: broken SSD door microswitches.''' The plastic tips snap off, almost always from prising the motherboard out with the SSD doors closed || Re-glue the broken tips, or recreate a missing tab from a scrap of ABS. '''Both switches must be repaired''' — fixing one is not enough.<ref name="rc3mx" />
|-
| '''SSDs not recognised — 3c''' || The 3c senses the doors with '''PCB tracks and a small metal connector on the door hinge''', not microswitches || Clean the tracks and the contact.<ref name="rc3mx" />
|-
| '''One slot works, the other does not''' || Slot contacts, or that slot's door sensing || Swap a known-good pack between slots to confirm before opening anything.
|-
| '''Flash SSD reads but will not format''' || The '''+16 V Vh''' converter || See the rail table above.<ref name="sibo" />
|-
| '''RAM SSD has lost its contents''' || Flat button cell inside the pack || Replace the pack's own cell.
|-
| '''Flash SSD reports itself full when it looks empty''' || Normal || Flash packs do not reclaim space until the whole pack is reformatted.<ref name="wp3" />
|-
| '''"Memory corruption" after a RAM upgrade''' || Incompatible SRAM devices || Original Sony parts are specified; at least one attempt with Hitachi 628128 devices produced exactly this message.<ref name="pb-ram">David Kimberlin-Wyer, [http://www.primrosebank.net/computers/pda/psion3a/projects/ram_upg/psion3a_mem_upg.htm "Psion Series 3a Memory Upgrade"], primrosebank.net. Source for the disassembly procedure, the board layout, the spare SRAM pads and the incompatible-memory result.</ref>
|-
| '''Machine resets or hangs unpredictably''' || '''Watchdog NMI''', or a marginal supply || The watchdog counts at 4 Hz and raises an NMI if not reset — about 0.75 s with interrupts disabled. A machine that keeps resetting is often a supply that is sagging under load.<ref name="sibo" />
|-
| '''Loses the time when the batteries are out''' || Normal on a Series 3; a fault on a 3a || The original Series 3 relies on the CPU waking periodically, so '''with no main batteries the time is lost'''. The 3a has a hardware 32-bit RTC and should keep time regardless.<ref name="sibo" />
|-
| '''Keys need a hard press''' || Dirty membrane or pads || Wash the membrane, clean the pads. See [[Psion Series 3a General Maintenance]].
|-
| '''A whole row or column of keys dead''' || Keyboard matrix line || The matrix is scanned by driving each column in turn and reading the rows, so a dead row is one line and a dead column is another.<ref name="sibo" />
|-
| '''Sticky, glue-like case''' || '''3c only''' — the rubberised soft-touch coating degrading || Strip with high-purity isopropyl alcohol. See [[Psion Series 3a General Maintenance]].
|-
| '''Corrosion, green tracks''' || Leaked AA cell || Neutralise and clean. See [[Battery Explosion, Capacitor or Corrosion Damage]].
|}

== What is realistically repairable ==

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Part !! Repairable? !! Notes
|-
| '''Battery lead''' || '''Yes''' || Re-seat or rewire. The highest-value repair on the machine.
|-
| '''Hinges''' || '''Yes''' || Epoxy, with or without a steel reinforcing strip.<ref name="mackay" />
|-
| '''Button bar ribbon''' || '''Yes''' || Often just needs reseating.<ref name="faq" />
|-
| '''Screen ribbon''' || Yes, with a donor lid || The cable is the failure, not the panel.
|-
| '''SSD door microswitches (3mx)''' || '''Yes''' || Superglue the broken tips; recreate a missing tab from ABS.<ref name="rc3mx" />
|-
| '''Keyboard membrane''' || Yes || Washable.
|-
| '''SRAM / ROM''' || Yes, for SMD-capable hands || Spare SRAM pads exist on 256 KB boards.<ref name="pb-ram" />
|-
| '''ASIC9''' || '''No''' || A Psion custom device. A failed ASIC9 means a donor board.
|}

== Related pages ==

* [[Psion Series 3a]] · [[Psion Series 3a General Maintenance]] · [[Psion Series 3a Hinge Repair]]
* [[Psion Series 3 Troubleshooting Guide]] · [[Psion Series 3c Troubleshooting Guide]] · [[Psion Series 3mx Troubleshooting Guide]] · [[Psion Siena Troubleshooting Guide]]
* [[Battery Explosion, Capacitor or Corrosion Damage]] · [[Recommended Tools]]

== References ==

<references />

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[[Category:Psion]]
[[Category:Troubleshooting Guides]]