Editing Psion Series 5mx Troubleshooting Guide

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[[File:Psion Series 5mx.jpg|thumb|420px|Two faults account for most dead 5mx machines: a cracked screen ribbon cable, and a broken hinge-wire hook. Both are documented and both are fixable.]]

Fault-finding for the '''[[Psion Series 5mx]]'''.

'''Start here.''' Almost every 5mx that "does not work" has one of five things wrong with it: flat or unsuitable batteries, the screen contrast set out of range, a cracked screen ribbon cable, a broken hinge-wire hook, or a sticky case-open microswitch. Work through those before opening anything.

== ⚠️ Before you start ==

* '''Back up first if the machine works at all.''' Removing both the main AA cells and the lithium backup cell without external power '''erases the internal memory'''.<ref name="s5sm">''Psion Series 5 Service Manual'', Psion Computers PLC, November 1997. Hosted on this wiki as [[:File:Psion Series 5 Service Manual (November 1997).pdf]]. Source for the ESD precautions, LCD handling warnings, reset behaviour, standby currents, battery-length note, and the Final Test explanations and Fail Ticket codes. Written for the Series 5; the 5mx shares the platform but not the electronics.</ref>
* '''Observe anti-static precautions.''' Psion's own manual devotes a page to it.<ref name="s5sm" />
* '''Do not bend the LCD module''' — its circuit board fractures, and the row drivers along the bottom edge break very easily.<ref name="s5sm" />
* '''If the LCD breaks''', keep the liquid crystal out of your mouth and eyes and wash it off skin immediately.<ref name="s5sm" />
* '''Use the stylus, not a metal tool''', to lever out the lithium cell — a metal tool can short it.<ref name="s5sm" />

== Backing up a machine with no usable screen ==

This is worth knowing before you touch anything, because it lets you rescue the data off a machine whose display has failed.

With the machine plugged into a serial cable and PsiWin running on the PC, work blind:<ref name="epocfaq">''The EPOC FAQ(ish)'', Series 5/5mx page, archived at the Internet Archive. Source for the blind-backup key sequence, the horizontal-lines diagnosis and cable suppliers, the vertical-swathe diagnosis, the contrast shortcuts, the stylus catch release, the case-open microswitch, and the battery current figure.</ref>

# Switch on and type the power-on password if the machine has one.
# Tap the '''System''' icon to be sure you are in the System screen.
# '''Ctrl-L''' to open the Link dialog.
# '''C''' to select "Cable".
# '''Down arrow''' to move to the baud rate.
# '''5''' to set 57600 — do not use "1", which could be 19200 or 115200.
# '''Enter''' to start the link and close the dialog.

Then right-click ''My Psion'' on the PC, check the connection settings match, and back up.

On a machine with a cracking ribbon, '''opening the lid only about a centimetre often restores the display''' long enough to do this with your eyes open.<ref name="r3uk">David Savery, [https://www.r3uk.com/index.php/tech-tips/34-disassembly-guides/9-psion-series-5mx-disassembly-and-screen-cable-repair "Psion Series 5MX disassembly and screen cable repair"], R3UK, 2004. Source for the ribbon cable failure mechanism, the partial-open workaround, the disassembly sequence, the ribbon colour identification, the location of the fracture, and the observation that temporary repairs do not last.</ref>

== Resets ==

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Reset levels'''
! Reset !! How !! Effect
|-
| '''Soft reset''' || Press the reset hole above the backup battery with an unfolded paperclip || Warm restart. '''User data should survive.'''<ref name="s5sm" />
|-
| '''Hard reset''' || Press the reset hole as above, then '''hold both Shift keys and press Esc''' to switch on || Clears the machine
|-
| '''Total loss of power''' || Remove main and backup cells for several minutes || Cold reset. '''Erases all volatile storage''' — everything on the C: drive
|}

The user reset switch is '''part of the backup battery's negative contact''', which is why it is only reachable with the backup battery cover open. Operating it vectors the CPU to a warm restart.<ref name="s5sm" />

A '''power-on (cold) reset''' is generated automatically by a voltage detector when the supply crosses its threshold, and it erases everything held in volatile storage.<ref name="s5sm" />

'''Note that a cold reset also loses your digitiser calibration''', because the user calibration lives in non-volatile memory rather than in the factory PROM.<ref name="s5sm" />

== The screen ribbon cable ==

This is '''the''' Series 5 and 5mx fault.

'''Symptom:''' horizontal lines across the display, appearing suddenly, often on opening the machine. Sometimes the display works if the lid is opened only part way.<ref name="r3uk" />

'''Cause:''' the flexible plastic ribbon that connects the mainboard to the screen '''cracks around a hole in the plastic''' that was used during manufacture to hold the cable in position. That hole is a stress raiser, and years of flexing the lid fracture the plastic around it. As soon as the fracture cuts a signal conductor, the display fails.<ref name="r3uk" />

The fracture is '''minute''' — expect to need a magnifying glass to see it. It is under the sticky black plastic covering the solder points at the screen end.<ref name="r3uk" />

'''The fix is a new cable.''' Temporary repairs — soldering a bridge across the broken track, or bonding a strand of ribbon from a scrap cable — do work, but they do not last: one documented attempt survived '''about four days''' of daily use.<ref name="r3uk" /> Aftermarket cables redesigned to remove the original design flaw have been produced by the community.<ref name="epocfaq" />

'''The 5mx uses a different screen ribbon from the Series 5.'''<ref name="r3uk" /> Check which machine you have before ordering.

Doing the job needs a fine-tipped iron, steady hands and patience: the solder points are tiny, and it is very easy to bridge adjacent pads. Check every joint with a continuity tester and clear splashes by running a blade between the pads.<ref name="r3uk" />

== Symptom table ==

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Psion Series 5mx — fault symptoms'''
! Symptom !! Likely cause !! Action
|-
| '''Horizontal lines across the display''' || '''Cracked screen ribbon cable''' || Replace the cable. See above.
|-
| '''Display works only when the lid is part-open''' || Cracked screen ribbon, not yet fully open-circuit || Back up immediately, then replace the cable.
|-
| '''A whole vertical swathe goes grey''' || '''One of the screen controller chips has failed''' || Not a cable fault. Needs a replacement screen assembly.<ref name="epocfaq" />
|-
| '''Screen simply blank''' || Contrast set out of range || Adjust with the keyboard shortcuts — '''Fn + N''' and '''Fn + M''' on the Series 5 family. Then try increasing levels of reset.<ref name="epocfaq" />
|-
| '''Blank after being somewhere very hot or cold''' || Contrast drifts with temperature || Adjust the contrast once the machine is back at room temperature before assuming a fault.<ref name="epocfaq" />
|-
| '''Will not switch on at all''' || Batteries; contrast; '''the case-open microswitch''' || Underneath the middle of the keyboard is a raised lump that presses a microswitch in the bottom case when the machine is closed. '''It can become sticky and fail to pop out under its own spring''', leaving the machine convinced it is shut.<ref name="epocfaq" />
|-
| '''Will not switch on, batteries known good, switch known good''' || Deeper fault || Try a very hard reset (remove all power for several minutes).<ref name="epocfaq" />
|-
| '''Lid does not open or close properly; screen flops''' || '''Broken hinge-wire hook in the chassis''' || See [[Psion Series 5mx Hinge Repair]].
|-
| '''Eats batteries''' || Unsuitable battery brand, or excessive current draw || Check the '''Battery Information''' screen: '''Shift-Ctrl-P''' in System. '''"Battery current now" should be below 50 mA''' with no external power and the backlight off. If it is higher, try a soft reset.<ref name="epocfaq" />
|-
| '''Intermittent low-battery warnings''' || '''Some battery brands are physically shorter''' than the European average and make poor contact || Try a different brand before suspecting the machine. Psion called this out specifically.<ref name="s5sm" />
|-
| '''Rechargeable AA cells give very short runtime''' || Expected || Psion note that rechargeables have very low usage time in this machine and can give the false impression it is draining them.<ref name="s5sm" />
|-
| '''Stylus will not click back into its slot''' || The catch has stuck closed inside the case || Slide something thin and stiff — a metal rule or a fingernail — into the gap in the case '''below the serial socket'''; you will hear the catch click open. Last resort, out of warranty: open the backup battery cover and '''slacken the screw under the warranty seal by half a turn''' to release it, then retighten.<ref name="epocfaq" />
|-
| '''Keyboard dead, or a block of keys dead''' || Keyboard flexi cable, its ZIF connector, or corrosion in the cable || Reseat the flexi squarely. Corrosion in the keyboard flex is a documented killer of otherwise good keyboards.<ref name="pitc">Point in the Cloud, [https://pointinthecloud.com/2025-10-13-154800.html "Repairing a Psion 5mx handheld computer to add to my collection"], 13 October 2025. Source for the modern disassembly notes, the metallised-plastic base observation, the corroded-vias and corroded-keyboard-flex findings, and the reassembly notes.</ref>
|-
| '''Touchscreen inaccurate''' || Calibration lost after total power loss || Recalibrate through the operating system. The factory calibration in the PROM is only a starting point.<ref name="wuffs">Ash Wolf (Ninji), [https://wuffs.org/blog/building-a-psion-emulator "\"16 Shades of Grey\" — Building a Psion/EPOC32 Emulator"], 27 December 2019. Source for the digitiser calibration storage, the PROM contents, the ETNA controller's role and the ADC channel arrangement.</ref>
|-
| '''Touchscreen dead in one axis''' || Digitiser connection or the digitiser itself || The digitiser has four connections sensing resistance across X and Y; one open circuit kills one axis.<ref name="s5sm" />
|-
| '''CompactFlash not detected''' || '''Door switch''', card seating, or the ETNA controller || Check the door switch first — the machine will not see the card with the door reported open. Select drive D: in the System window and open and close the door to watch the disk appear and disappear.<ref name="s5sm" />
|-
| '''Machine crashes intermittently''' || Dry or faulty joints on the daughter (ROM) PCB || Psion specifically call this out: '''intermittent faults can be caused by dry or faulty joints on the daughter PCB'''. It unclips and eases out of its socket for a quick swap test.<ref name="s5sm" />
|-
| '''Corroded board, green vias''' || Past battery leak || Often terminal. Clean and inspect, but a board with green vias may be beyond saving.<ref name="pitc" />
|-
| '''Speaker or microphone dead''' || Speaker flexi connector || It disconnects by lifting the tags on the sides of the connector; reseat it.<ref name="s5sm" /><ref name="r3uk" />
|-
| '''Serial link will not connect''' || Baud rate mismatch, cable, or the expansion connector || Set the link explicitly to 57600 rather than trusting a saved setting.<ref name="epocfaq" />
|}

== Factory test fault codes ==

Psion's Final Test unit printed a numeric "Fail Ticket" code for each failure. The table below is Psion's own fault-to-cause mapping, and it remains a useful checklist even without the test rig — it tells you what Psion themselves expected to fail, and which assembly to suspect.<ref name="s5sm" />

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Series 5 Final Test Fail Ticket codes'''<ref name="s5sm" />
! Code !! Test !! What to check !! Assembly to change
|-
| '''01''' || Too much current || — || PCB
|-
| '''03''' || No response to the wake-up signal || Battery module contacting the positive contact; battery spring clip present; expansion connector DSR/DTR || PCB battery spring; PCB expansion connector
|-
| '''04''' || Failed Tx/Rx communication || CompactFlash fully inserted; CF door fully shut and the device detected; ROM board connections; expansion connector Tx/Rx; '''lithium reset contact stuck down''' || Door switch and its plastic cam; ROM board connector; expansion connector; bend the lithium contact away from the PCB
|-
| '''06''' || Language / RAM size || Test setup || Wrong unit build
|-
| '''07''' || Standby current out of limits || '''DRAM on the PCB'''; dry joints and floating inputs; '''shorts caused by metallisation of the plastics onto the PCB''' || PCB; dictaphone plastics
|-
| '''08, 10''' || LCD connector || — || LCD
|-
| '''09''' || Backlight connector || — || Backlight
|-
| '''11''' || Keyboard connector, keys || — || Keyboard
|-
| '''12, 13''' || Expansion connector Tx/Rx, and RTS/DTR/CTS/DSR/DCD || — || PCB expansion connector
|-
| '''14''' || IrDA not blocked || — || PCB IrDA devices
|-
| '''15''' || Lithium cell in socket; dry joints on the lithium contacts || — || PCB; lithium contacts
|-
| '''16''' || DC jack lead properly inserted || — || PCB DC jack socket
|-
| '''17, 18, 19''' || Expansion connector Vin2+/ground, shield, Vpc || — || PCB expansion connector
|-
| '''22''' || Speaker fitted correctly || — || Speaker
|-
| '''23''' || Microphone fitted || — || PCB microphone
|-
| '''24, 27''' || Case switch stuck open / stuck closed || — || '''PCB case switch'''
|-
| '''25''' || Digitiser connections || — || Digitiser
|-
| '''26''' || Action of the dictaphone buttons || — || Plastics; PCB dictaphone switches
|-
| '''28''' || Dictaphone status LED || — || PCB status LED
|-
| '''29''' || Plastic cam operator of the CompactFlash door || — || Plastics; PCB CF door switch
|-
| '''33''' || ROM board devices || Test setup || Wrong unit build
|}

Two entries there are worth reading twice. '''Code 07''' blames excess standby current partly on "'''shorts caused by metallisation of plastics onto the PCB'''" — the case mouldings are metallised for EMC, and flakes of that plating shorting onto the board is a real and documented failure mode. And '''code 04''' includes "'''lithium reset contact permanently down'''", with the fix being to bend the contact away from the PCB — a machine that behaves as though it is being reset constantly may have exactly that.

== Current measurements ==

Psion's published standby figures are for the '''Series 5''', measured with the processor asleep at 2.75 V. They are still a useful order-of-magnitude reference for the platform:<ref name="s5sm" />

{| class="wikitable styled-table" style="width:60%; text-align:left;"
|+'''Series 5 standby current'''<ref name="s5sm" />
! Model !! Standby current
|-
| 4 MB || 1.50 mA
|-
| 8 MB || 2.10 mA
|}

For a running machine, the check to use is the operating system's own: '''Shift-Ctrl-P''' in System shows Battery Information, and '''"Battery current now" should be below 50 mA''' with no external power and the backlight off.<ref name="epocfaq" />

== What is realistically repairable ==

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Part !! Repairable? !! Notes
|-
| '''Screen ribbon cable''' || '''Yes''' || The standard repair. Aftermarket redesigned cables exist. 5mx and Series 5 cables differ.
|-
| '''Inner chassis / hinge hooks''' || '''Yes''' || 3D-printed replacements are available — see [[Psion Series 5mx Hinge Repair]].
|-
| '''Keyboard''' || Yes, with a donor || Supplied as a complete assembly. Language-specific.
|-
| '''LCD / digitiser''' || Yes, with a donor || Psion recommend replacing the LCD and digitiser as a single assembly, because the conductive strip and the clamp are placed with factory equipment and are very hard to fit accurately by hand.<ref name="s5sm" />
|-
| '''Backlight''' || Fragile || Psion warn it is easily damaged during servicing; check it whenever the screen is apart.<ref name="s5sm" />
|-
| '''Daughter (ROM) PCB''' || Yes, with a matching donor || '''Must be the same OS build number and language.''' Check with '''Ctrl+H''' in the System screen before swapping.<ref name="s5sm" />
|-
| '''Mainboard''' || Board-level swap only || Psion themselves recommend board-level rather than component-level repair. A replacement must have the same RAM size.<ref name="s5sm" />
|-
| '''ETNA (CompactFlash controller)''' || '''No''' || A bespoke, undocumented Psion part.<ref name="wuffs" />
|}

== Related pages ==

* [[Psion Series 5mx]]
* [[Psion Series 5mx General Maintenance]]
* [[Psion Series 5mx Hinge Repair]]
* [[Psion Series 5mx Capacitor Replacement Guide]]
* [[:File:Psion Series 5 Service Manual (November 1997).pdf|Psion Series 5 Service Manual]]
* [[Battery Explosion, Capacitor or Corrosion Damage]] · [[Recommended Tools]]

== References ==

<references />

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