Psion Series 5mx Troubleshooting Guide
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
edit- 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.[1]
- Observe anti-static precautions. Psion's own manual devotes a page to it.[1]
- Do not bend the LCD module — its circuit board fractures, and the row drivers along the bottom edge break very easily.[1]
- If the LCD breaks, keep the liquid crystal out of your mouth and eyes and wash it off skin immediately.[1]
- Use the stylus, not a metal tool, to lever out the lithium cell — a metal tool can short it.[1]
Backing up a machine with no usable screen
editThis 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:[2]
- 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.[3]
Resets
edit| Reset | How | Effect |
|---|---|---|
| Soft reset | Press the reset hole above the backup battery with an unfolded paperclip | Warm restart. User data should survive.[1] |
| 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.[1]
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.[1]
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.[1]
The screen ribbon cable
editThis 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.[3]
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.[3]
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.[3]
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.[3] Aftermarket cables redesigned to remove the original design flaw have been produced by the community.[2]
The 5mx uses a different screen ribbon from the Series 5.[3] 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.[3]
Symptom table
edit| 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.[2] |
| 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.[2] |
| 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.[2] |
| 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.[2] |
| Will not switch on, batteries known good, switch known good | Deeper fault | Try a very hard reset (remove all power for several minutes).[2] |
| 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.[2] |
| 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.[1] |
| 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.[1] |
| 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.[2] |
| 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.[4] |
| Touchscreen inaccurate | Calibration lost after total power loss | Recalibrate through the operating system. The factory calibration in the PROM is only a starting point.[5] |
| 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.[1] |
| 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.[1] |
| 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.[1] |
| Corroded board, green vias | Past battery leak | Often terminal. Clean and inspect, but a board with green vias may be beyond saving.[4] |
| Speaker or microphone dead | Speaker flexi connector | It disconnects by lifting the tags on the sides of the connector; reseat it.[1][3] |
| 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.[2] |
Factory test fault codes
editPsion'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.[1]
| 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
editPsion'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:[1]
| 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.[2]
What is realistically repairable
edit| 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.[1] |
| Backlight | Fragile | Psion warn it is easily damaged during servicing; check it whenever the screen is apart.[1] |
| 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.[1] |
| Mainboard | Board-level swap only | Psion themselves recommend board-level rather than component-level repair. A replacement must have the same RAM size.[1] |
| ETNA (CompactFlash controller) | No | A bespoke, undocumented Psion part.[5] |
Related pages
editReferences
edit- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 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.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 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.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 David Savery, "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.
- ↑ 4.0 4.1 Point in the Cloud, "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.
- ↑ 5.0 5.1 Ash Wolf (Ninji), "\"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.