Psion Series 5mx General Maintenance

The 5mx. Everything that goes wrong with these machines is mechanical or connector-related, and most of it is preventable.

Preventive maintenance for the Psion Series 5mx.

The 5mx is electrically reliable and mechanically fragile. There is no capacitor plague, no notorious chip and no recap tradition — what fails is the screen ribbon cable, the hinge-wire hooks, the flat flexible cable connectors and, if you neglect the batteries, the board.

Most of that is preventable. This page is about the habits that keep a 5mx alive.

⚠️ Safety and data

• Back up regularly, and always before opening the machine. Removing both the main AA cells and the lithium backup cell without external power erases the internal memory — everything on the C: drive.
• Use the stylus, not a metal tool, to lever the lithium cell out of its location. A metal tool can short it.
• There is a danger of explosion if the lithium battery is incorrectly replaced. Fit only the same or an equivalent type.
• Observe anti-static precautions whenever the machine is open.
• Never bend the LCD module. Its circuit board fractures, and the drivers along its bottom edge break very easily.

Batteries

The 5mx runs from two AA cells with a lithium coin cell backing up the RAM disk.

Routine

• Change the AA cells before they are completely flat, and change them one machine-state at a time — the backup cell is doing the work while they are out, so it needs to be good.
• Replace the backup lithium cell on a schedule, not on failure. It is cheap and it is the only thing standing between you and total data loss during an AA change.
• Take both cells out for long-term storage — after backing up — and store the machine with the compartments open and dry. A leaking AA in a 5mx destroys the board.
• Some battery brands are physically shorter than the European average and make poor contact, which produces spurious low-battery warnings. Psion called this out explicitly.
• Rechargeable AA cells give very short runtime in this machine, which can give the false impression it is draining them.

Health check

Shift-Ctrl-P in the System screen shows Battery Information. "Battery current now" should be below 50 mA with no external power and the backlight off. Anything higher is worth investigating, and a soft reset often clears it.

If a machine has leaked, deal with it before anything else — see Battery Explosion, Capacitor or Corrosion Damage. Green vias on a 5mx board are a bad sign and frequently terminal.

Looking after the hinge

This is the single most valuable habit. The spring hinge wires are retained by small plastic hooks moulded into the inner chassis, and those hooks embrittle under constant tension and eventually break. Opening the machine badly accelerates it.

• Open the machine with two hands, lifting the lid squarely, and let the sliding mechanism do its work. Do not flip it open one-handed by a corner.
• Do not force the lid past its stop or hold it open against the spring.
• Do not carry it open.
• Do not close it on a stylus, a cable or a card.
• Inspect the hooks whenever the machine is open for repair. A whitening line at the root of a hook is the warning.

When a hook does break, the chassis can be replaced with a 3D-printed part — see Psion Series 5mx Hinge Repair.

Looking after the screen ribbon

The screen ribbon cracks around a hole left in the plastic by the manufacturing process, and years of opening and closing the lid do the damage.

There is no way to eliminate that, but you can slow it:

• Open the lid to a comfortable angle and leave it there rather than adjusting it constantly.
• Avoid opening and closing the machine repeatedly to check something — use the machine open.
• Back up regularly, because the failure arrives without warning.
• When you do open the machine for other work, inspect the ribbon at the screen end under magnification. A crack found early can be planned for rather than reacted to.

Doors, catches and switches

The moving parts, and what they need

Part	Maintenance
Battery door	Psion applied a small amount of silicone-based lubricant on the running surface at both ends during manufacture, to help the rotating action. A replacement or a stiff original should be treated the same way.
CompactFlash door	Operates a switch the machine relies on. Keep it clean and check it moves freely; the machine will not see a card while the door reads as open.
Case-open microswitch	A raised lump under the middle of the keyboard presses a microswitch in the bottom case when the machine is closed. It can become sticky and fail to pop out, so the machine behaves as though it is still shut and will not switch on. Work it and clean around it.
Stylus catch	If the stylus will not click back in, the catch has stuck closed. Slide something thin and stiff into the gap in the case below the serial socket until you hear it click open.
Pen eject mechanism	Its spring drops out if you are careless when replacing the base. Check it is seated before closing up.
Dictaphone buttons	Should press in and release easily of their own accord. A sticky button that needs help to release is a fault, not something to work loose by force.

Connectors and cables

Everything inside the 5mx connects with flat flexible cables in ZIF or LIF sockets, and they are the most abused parts of the machine.

• Open the retaining slider before pulling any cable, and close it fully afterwards.
• Insert cables squarely. Psion warn that inserting a flexi at an angle causes short or open circuits, and that the existing bends in the cables must be retained so the components line up correctly on the mainboard.
• On the 5mx, the blue cable is the keyboard and the brown cable is the screen; Psion's Series 5 manual describes them as blue for keyboard and orange for LCD.
• Corrosion inside a keyboard flexi kills the keyboard and is not repairable — check for it before blaming the keyboard assembly.
• Clean the CompactFlash and serial connectors with a foam swab and isopropyl alcohol. Keep the serial door closed.
• Keep the IrDA window clean and unscratched.

Case and screen

• Clean the case with a barely damp cloth. The case mouldings are metallised for electromagnetic compatibility, and aggressive cleaning can damage the coating — flakes of that plating shorting onto the PCB is a fault Psion themselves listed.
• Clean the touchscreen with a soft dry cloth. It is a hardened plastic top plate over glass, and solvents will haze it.
• Use a proper stylus, not a pen or a fingernail. The resistive digitiser is worn by point loads.
• Keep the screen out of direct sunlight for long periods.
• Do not stack anything on a closed 5mx.

Capacitors

The 5mx is not a recap candidate. See Psion Series 5mx Capacitor Replacement Guide for why, and for the small number of cases where capacitor work is justified.

Preventive maintenance checklist

1. Back up to a PC or a CompactFlash card.
2. Replace the lithium backup cell if you do not know its age.
3. Inspect the AA compartment and contacts for corrosion.
4. Check "Battery current now" is under 50 mA with the backlight off.
5. Open and close the machine and check the lid snaps positively at both ends of its travel.
6. Confirm the case-open microswitch releases cleanly.
7. Check the stylus clicks in and out.
8. Check the CompactFlash door operates its switch — watch drive D: appear and disappear.
9. Clean the touchscreen, the IrDA window and the serial connector.
10. If the machine is being opened anyway, inspect the screen ribbon and the hinge hooks under magnification.

Recommended tools

• Jeweller's screwdrivers, including a very thin one, and a 2.5 × 35 mm Phillips for the case screws.
• Plastic spudgers and a scalpel or sharp craft blade.
• Fine pliers; Psion's own list includes micro shear pliers.
• Anti-static strap.
• Magnifier or a loupe — essential for inspecting the ribbon.
• Isopropyl alcohol, lint-free swabs, foam swabs.
• Silicone-based lubricant for the battery door running surfaces.
• Fresh alkaline AA cells and a spare lithium backup cell.
• A serial cable and a PC running PsiWin, or a CompactFlash card and reader, for backups.

See Recommended Tools for the general workshop kit.

Related pages

• Psion Series 5mx
• Psion Series 5mx Troubleshooting Guide
• Psion Series 5mx Hinge Repair
• Psion Series 5mx Capacitor Replacement Guide
• Psion Series 5 Service Manual
• Battery Explosion, Capacitor or Corrosion Damage · Recommended Tools