Psion Series 3 Troubleshooting Guide

A Series 3. Diagnose the battery lead before anything else — it is the fault that makes these machines eat cells, and it is invisible from the outside.

Fault-finding for the Psion Series 3 (1991).

The full symptom table, the SIBO power states and the supply rail chart are in the Psion Series 3a Troubleshooting Guide, which applies to this machine too. This page covers what is different about the original Series 3, and the faults that behave differently on it.

⚠️ Before you start

• Back up first. Diagnosis means removing batteries, and RAM contents do not survive.
• Open both SSD doors before lifting the mainboard.
• Anti-static precautions throughout.
• Note the time. A Series 3 will lose it — see below.

The three-chip difference

The Series 3 uses V30H + ASIC1 + ASIC2 rather than the 3a's integrated ASIC9. That changes the diagnosis in three useful ways.

1. The fault can be localised between two chips

Which chip owns which function

Function	Chip	Symptom when it fails
Bus control, memory and I/O decoding	ASIC1	Machine dead or immediately crashing
LCD controller and timing	ASIC1	Blank, scrambled or badly timed display with a healthy Vcc3
System timer and interrupt controller	ASIC1	Hangs, no tick, software that never resumes
Watchdog	ASIC1	Repeated unexplained resets
System clock oscillator	ASIC2	Completely dead — nothing runs
On/off control (standby ↔ operating)	ASIC2	Will not switch on, or will not switch off
Keyboard scanning	ASIC2	Whole keyboard dead while the machine otherwise runs
Buzzer	ASIC2	Silent machine
SSD and expansion serial channels	ASIC2	No packs recognised at all
NMI generation (power fail, SSD and expansion door switches)	ASIC2	Spurious resets, or doors not detected

2. A "frozen" machine may be doing what it is told

ASIC1 stops the processor clock on a HALT instruction and holds it stopped until an interrupt or NMI arrives. A Series 3 that appears completely locked up but is not hot and is drawing very little current may be waiting for an interrupt that is never going to come — which points at the interrupt source, not at the CPU.

3. The clock is lost without main batteries

The Series 3 has no hardware RTC. It keeps time by waking the CPU roughly every eight hours. With no main batteries the CPU cannot start, and the time is lost.

This is normal behaviour and not a fault. A 3a or later, which has a hardware 32-bit RTC, will keep time regardless — so "loses the clock when the batteries are out" is a fault on a 3a and expected on a Series 3.

Series 3-specific symptoms

Symptom	Assessment
Clock wrong after storage with the cells out	Normal. See above.
Will not record sound	Normal. The Series 3 has a piezo buzzer and no microphone; recording arrived with the 3a.
No comms software on the machine	Normal. On the Series 3 the comms software lives in the link pod's ROM, not in the machine.
Screen looks coarse compared with a 3a	Normal. 240 × 80, black and white, no grey plane.
A 3a lid does not fit / does not work	Expected. Different panel, different ribbon. Source a Series 3 donor.
Eats batteries at a phenomenal rate	The battery lead. The lead between mainboard and battery contacts is twisted every time the lid opens, the wires fatigue and short. Remove the screws behind the batteries and re-seat the two-pin connector; rewire if damaged.
Vertical lines on the display	Screen ribbon deterioration.
Button bar dead	Ribbon adrift from the lower PCB. Push it home with a paperclip, lid half closed.
Back edge crooked on opening	Broken hidden hinge. See Psion Series 3 Hinge Repair.

For everything else — the full symptom table, the four power states, the supply rail chart, SSD faults and what is realistically repairable — see Psion Series 3a Troubleshooting Guide.

Related pages

• Psion Series 3 · Psion Series 3 General Maintenance · Psion Series 3 Hinge Repair
• Psion Series 3a Troubleshooting Guide — the shared diagnostic material
• Battery Explosion, Capacitor or Corrosion Damage · Recommended Tools