Psion Series 5mx Hinge Repair

The mechanism that makes the machine, and the mechanism that breaks it. Opening the lid slides the keyboard forward under spring tension; the spring wires are retained by small plastic hooks moulded into the inner chassis, and those hooks are what fail.

The single most common mechanical failure on a Psion Series 5 or 5mx is a broken hinge-wire hook in the inner chassis. This guide explains the failure, why the usual bodges are unsatisfying, and how to replace the chassis with a 3D-printed part.

The failure

The machine has a pair of spring hinge wires, one on each side, which provide the tension that makes the lid snap open and snap shut and that drives the keyboard forward as it opens. Psion's own parts list names them Hinge Wire LH (8405-0012-01) and Hinge Wire RH (8405-0013-01), retained by Hinge Wire Staples (8405-0011-01), all mounted on the CPU Chassis (2902-0010-01).

The chassis moulding carries small hook retainers that secure the ends of those spring wires. In old machines those hooks become brittle under the constant high tension and eventually snap; opening the machine carelessly accelerates it. Once a hook goes, the wire floats free and the lid no longer opens or closes correctly.

It gets worse, not better. The centre wire fasteners degrade in the same way, and close inspection shows the spring wires cracking the plastic around them. Once one hook has gone, the others are on the same trajectory.

Why not just glue or bodge it

Two workarounds are documented, and both work after a fashion:

• Drill a small hole through the side — checking first that no ribbon cable is behind it — and thread a piece of wire through to tie the hinge wire down. The same trick can be used at the centre fasteners.
• Drill a hole in the back piece and twist a piece of solid electrical wire to hold the hinge wire, folding the twist inside where it is hidden on reassembly.

Neither addresses the underlying problem, which is that the whole moulding is embrittled, and neither is easy to reverse. There is also a specific reason gluing a printed hook onto the original chassis is unlikely to hold: the base is a metallised plastic — almost certainly plated for electromagnetic compatibility — so an adhesive joint has to bond to a metal film rather than to the plastic itself, at a point carrying real spring load.

Replacing the chassis outright is the better answer, and until recently that meant finding a donor machine.

The printed replacement

A complete printable inner chassis for the Series 5mx is published on MakerWorld by ivor.hewitt (released 13 June 2026). It is a remix of "Psion 5MX — Internal housing / hinge panel" by Jon on Printables, which was incomplete; the remix adds and corrects the hinges, adds a hole for the battery cover, and updates the holes for M2 screws.

Both models are licensed Creative Commons Attribution–NonCommercial–ShareAlike, so print them for yourself, credit the authors, and do not sell the prints.

Which version to print

The model is published with four print profiles. Two of them slice the chassis into a tray plus a separate hinge spine; the other two print it as one piece.

Published print profiles

Profile	Settings	Time	Notes
Sliced, AMS	0.2 mm layer, 2 walls, 15 % infill	3.3 h	Chassis and hinge spine as separate parts
Sliced, no AMS	0.2 mm layer, 2 walls, 15 % infill	1.8 h	As above, single material
Single piece	0.2 mm layer, 2 walls, 15 % infill	3.6 h	Recommended
Fine	0.2 mm nozzle, 0.1 mm layer, 4 walls, 15 % infill	17.8 h	Slowest, finest detail

Print the single-piece version. The two-part versions are quicker and easier to print, but they put a joint exactly where the spring wires apply their load — which is the failure you are trying to eliminate.

Orientation

Print it standing up, so the layer lines run along the length of the hinge spine rather than across it.

This is the whole point. A part printed flat has its layer boundaries lying perpendicular to the direction in which the spring wires pull on the hooks, and FDM parts are weakest exactly there — the hook does not break, it peels off along a layer line. Standing the part up puts the extruded filament along the load path instead of across it.

It costs you a longer print and more support material. Take that trade.

Material

PLA is not adequate for this part. It creeps under sustained load — which is exactly what a spring wire applies — and it goes brittle with age, reproducing the original failure.

Use one of:

Recommended materials

Material	Why	Watch out for
PETG	Tough, good layer adhesion, forgiving to print, does not creep the way PLA does	Stringing; dry the filament. Slightly flexible, which is fine here.
ABS	Strong, stiff, good under sustained load, and can be vapour-smoothed	Warping — needs an enclosure. Ventilate.
PC (polycarbonate)	The strongest and stiffest of the three, and the best choice if your printer can manage it	High nozzle and bed temperatures; needs an enclosure and dry filament.

Print hot enough for good layer adhesion rather than for a pretty surface finish. This is a structural part; interlayer bonding is the whole specification.

Consider raising the wall count above the profile's default of 2 — 3 or 4 walls puts more solid material into the thin hook features, at very little cost in time.

Fasteners

The model's holes are sized for M2 screws. Recover the original screws if they are in good condition; otherwise M2 machine screws of the right length will do. Do not over-tighten — the original service manual warns that the case screws purchase into the chassis moulding and strip easily, and that is even truer of a printed part.

⚠️ Before you start

• Back up the machine first if it still works. Removing both the main cells and the backup cell without external power erases the internal memory.
• Observe anti-static precautions. The machine is full of CMOS devices.
• Do not bend the LCD module. Its circuit board fractures easily, and the drivers along the bottom edge of the panel are very fragile.
• If the LCD does break, do not get liquid crystal in your mouth or eyes; wash it off skin or clothing immediately with soap and plenty of water.
• Work over a tray. There are small springs and pins in this machine that will not be seen again if they escape.

Disassembly

This sequence combines Psion's own procedure with the practical notes of people who have done it recently.

Tools

• Jeweller's screwdrivers, including a very thin one
• A scalpel or a sharp craft blade
• Plastic spudgers
• A pair of fine pliers
• Anti-static strap
• Optionally a drop of WD-40 or similar

Steps

1. Remove the stylus, the main AA cells, the backup lithium cell and any CompactFlash card. Use the stylus, not a metal tool, to lever the lithium cell out — a metal tool can short it.
2. Open the battery door and the CompactFlash door, and remove the three case screws: one in each door and one by the battery compartment door. One is under the warranty label, which will be destroyed.
3. Free the base moulding with a spudger, starting at the rear, and lift it away. Leaving both doors open frees locating clips between the PCB and the base moulding.
4. Remove the hinge cover / battery compartment moulding. It is held by two clips towards the top-centre; slide a spudger in there to free it. Psion's method is to insert a blunt point into the centre of the hinge moulding and lever it out of its clips with the battery door closed.
5. Remove the three screws holding the main PCB, then disconnect the speaker flexi by lifting the tags on the sides of its connector and easing the ribbon out.
6. Ease the PCB partly out, then open the machine for better access to the remaining ribbons. Placing the assembly on the edge of a slightly raised surface — a book will do — lets the PCB drop and gives the flexis more slack.
7. Disconnect the screen and keyboard flexis. On a 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. Open the retaining sliders on each connector before pulling.
8. Separate the screen from the keyboard before trying to free the hinge wires. Trying to unhook the wire first is the point at which most people get stuck. Start the friction-held pin that joins keyboard to screen with a scalpel blade, then, once there is room, pry it out with a jeweller's screwdriver. Repeat on the other side.
9. Feed the hinge wire through and around its clip until the screen is free.
10. Remove the spring wire hinge pins. These are cylindrical tubes. Psion specified a special tool that no longer exists; instead, insert a thin precision screwdriver shaft into the tube and wiggle while pulling. A couple of drops of penetrating oil helps.
11. The chassis is now bare. Photograph it from every angle before you go further.

Psion's own manual suggests cutting away the plastic moulding that covers the LCD/keyboard hinge pin to expose it. You do not need to do this if you use the blade technique above — the pin has a head that a sharp edge can get purchase on.

Fitting the printed chassis

1. Dry-fit first, with nothing else attached. Check the screw holes line up, the hinge tube bores accept the pins, and the battery cover aperture is clear.
2. Clean up the print. Remove supports, clear the screw holes and the hinge bores with a drill bit turned by hand, and deburr the hook features. Do not force a pin into a tight bore — open the bore instead.
3. Test the hooks with the spring wires before assembling anything else. Hook each wire and flex it a few times. A hook that flexes visibly, or that shows a whitening line at its root, needs a stronger print.
4. Transfer the original parts: the hinge wires and their staples, the pivot arm pins, and any labels or foam you removed.
5. Reassemble in reverse order.

Reassembly cautions

• Insert the flat flexible cables squarely. Psion warn that inserting an FFC at an angle can cause short or open circuits, and that the existing bends in the cables must be retained so everything lines up on the mainboard.
• Watch the pen eject mechanism. Its spring drops out if you are not careful while replacing the base.
• Have the machine open when refitting the mainboard and the base, so the on/off and door-warning switches are not fouled.
• Leave the CompactFlash and battery doors open during reassembly.
• Do not over-tighten the case screws. They bite into the chassis — in this case, into your print.
• Expect to need patience. As one recent account put it, the original designer appears to have had three arms.

Verifying the repair

1. Open and close the machine twenty times. The lid should snap open and snap shut crisply, and the keyboard should slide fully forward and fully back each time.
2. Check the keyboard sits flush when closed. If it stands proud, a hinge wire is not seated.
3. Press the touchscreen firmly with the machine open on a desk. It should not tip — that bracing is the whole purpose of the mechanism.
4. Check the case switch. There is a raised lump under the middle of the keyboard that presses a microswitch when the machine is closed; confirm the machine sleeps when shut and wakes when opened.
5. Inspect the hooks again after a week of use. If a printed hook is going to fail it will show early.

Related pages

• Psion Series 5mx
• Psion Series 5mx General Maintenance
• Psion Series 5mx Troubleshooting Guide
• Psion Series 5 Service Manual
• Recommended Tools