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Psion Series 5mx Capacitor Replacement Guide

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Psion Series 5mx
Psion Series 5mx

The Psion Series 5mx (1999) runs from two AA cells on a dense surface-mount main board.[1][2] Psion published no component-level parts list for the Series 5 or 5mx main board, so there is no capacitor list to work from. Its Series 5 service manual lists spares only as assemblies (main board, ROM board, LCD, keyboard, chassis) and recommends repair at circuit-board level because of the high-density surface-mount construction.[2] The faults recorded on these machines are mechanical, or corrosion on the board and its flat cables; see Psion Series 5mx Troubleshooting Guide.

Visual inspection and failure signs

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  • Corrosion on the board or the flat cables. One 5mx Pro board that booted once and then hung had green, corroded vias, and its keyboard flat cable had corroded and no longer worked in any machine.[3] See Battery Explosion, Capacitor or Corrosion Damage.
  • Excessive battery drain. In the System screen, Battery Information (Shift-Ctrl-P) should show a battery current below 50 mA with no external power and the backlight off.[4] Switched off, the 5mx uses about 1 % of its battery charge per day.[1]
  • Excessive standby current. On the Series 5, Psion's Fail Ticket code 07 gives the causes as the DRAM, dry joints or floating inputs, and shorts from the metallised plastics onto the board.[2] The 5mx base is also metallised plastic.[3]
  • Too much current at switch-on. Psion's Series 5 final test powers the machine at 2.50 V with a 65 mA current limit and requires the current to be below 10 mA before it continues; Fail Ticket code 01, "too much current", points at the main board.[2]

Capacitor list

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No capacitor list exists for the 5mx: Psion did not publish component values for the Series 5 or 5mx boards, and the service manual's exploded views stop at assemblies.[2] If a capacitor is found damaged, identify it from the board itself and measure a matching part on a donor board.

Replacement procedure

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  1. Back up. Removing both the main cells and the backup cell erases the machine.[1]
  2. Work on an earthed mat with a wrist strap; the boards are CMOS.[2]
  3. Open the battery and CompactFlash doors, remove the three case screws and lift off the base, then remove the battery moulding, the three main board screws and the speaker, LCD and keyboard flat cables.[3][5]
  4. Do not bend the LCD module or the ROM daughter board; Psion warns that both circuit boards are prone to fracture.[2]
  5. Clean corrosion and replace only the parts that are damaged.
  6. Reassemble with the CompactFlash and battery doors open, and insert the flat cables squarely into their sockets.[3][2]

Post-repair checks

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Checks after work on the board
Check Expected
Battery current in Battery Information, no external power, backlight off Below 50 mA[4]
Charge used while switched off About 1 % per day[1]
Display, keyboard, CompactFlash (drive D) with the door closed All working[2]
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References

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  1. ↑ 1.0 1.1 1.2 1.3 Psion Computers PLC, Series 5mx User Guide, Version 1.1, October 1999, part no. 6105-0053-01. Hosted on this wiki as File:Psion Series 5mx User Guide (October 1999).pdf. Batteries (pp. 176–179) and specification (p. 191).
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Psion Computers PLC, Series 5 Service Manual, November 1997. Hosted on this wiki as File:Psion Series 5 Service Manual (November 1997).pdf; see Psion Series 5 Service Manual. Introduction and board-level repair recommendation (PDF p. 4), exploded views and spares kits (pp. 9–16), disassembly precautions and daughter board removal (pp. 17–19), final test current limits (p. 43) and Fail Ticket codes (p. 45). Written for the Series 5, before the 5mx.
  3. ↑ 3.0 3.1 3.2 3.3 Point in the Cloud, "Repairing a Psion 5mx handheld computer to add to my collection", 13 October 2025. Corroded vias and keyboard flex, the metallised base and the hinge-wire repair.
  4. ↑ 4.0 4.1 "Series 5mx/5/MC218 specific", The EPOC FAQ(ish). The Battery Information screen and its 50 mA figure.
  5. ↑ David Savery, "Psion Series 5MX disassembly and screen cable repair", R3UK, 6 July 2004. 5mx disassembly steps 1–7.


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