Psion Organiser II Troubleshooting Guide

Establish which machine you have before you start. The four-line LZ and LZ64 use a different control IC and different LCD drivers from the two-line CM, XP and LA.

Fault-finding for the Psion Organiser II.

Psion's Technical Manual documents the supply rails, the operating states, the power-on sequence and the expected currents in enough detail to diagnose this machine properly rather than by substitution. This page combines that with what the community has found in practice.

⚠️ Before you start

• Remove the battery before opening anything.
• Back up to a Datapak first if the machine still works at all. RAM contents do not survive a long battery removal.
• Never insert or remove a Rampak with the machine switched on. The sudden power drop corrupts data.
• Everything on the system board is CMOS. Use an anti-static strap.
• The SVPP rail reaches 21 V during Datapak writes, from a capacitor charged towards 35 V. Harmless to you, fatal to a pack if applied at the wrong moment.

Step 1: Identify the machine

If it powers up at all, get this out of the way first. From the main menu choose CALC and evaluate:

• PEEKB(-24) — model: 0 = CM, 1 = XP, 2 = XP(LA), 14 = LZ, 13 = LZ64. Values of 17–20, 29, 30, 65, 66, 129 and 130 are POS and industrial variants.
• PEEKB(-23) — ROM version in BCD, so $46 is version 4.6.
• PEEKB(-25) — language options.

This matters because the LZ/LZ64 use a Texas Instruments CF70043 control IC and HD66780/HD66100 LCD drivers, while the earlier machines use an NEC µPD65006 and HD44780/HD44100. Boards are not interchangeable across that divide.

Step 2: Rule out the four usual suspects

Before any measurement:

1. Battery. Fit a known-good alkaline PP3 and check it under load, not just off-load. A cell that reads 9 V open-circuit and collapses under a 200 mA peak will produce completely misleading symptoms.
2. Contrast. Sweep the thumbwheel through its full travel, slowly. On a tired display the usable band is narrow.
3. Packs. Remove every pack and try again. A shorted or damaged pack can hold the whole machine down.
4. AC key. If AC is dirty or dead, nothing will switch the machine on — it is the only key not in the scanned matrix.

Step 3: Understand what should happen at switch-on

Knowing the sequence tells you where it stopped.

1. Pressing AC (or a rising edge on the external AC input, or a timeout of the stage 2 counter) sets the ON/OFF latch in the control IC.
2. ON_B goes low immediately, switching on the supply rail regulators.
3. After a delay for the rails to settle, the processor is brought out of standby by sequencing STBY_B and RES_B: it sits in reset for 30 to 60 ms while the oscillator and E clock start, then runs.
4. The processor initialises the LCD — the display drivers lose power when the machine is off, so the LCD is re-initialised every time.
5. Shutdown is initiated by the processor itself, by accessing the SWITCH OFF address at $01C0–$01FF.

So: no rails at all is a power board or ON/OFF latch problem; rails present but no display is the processor, the ROM or the LCD; display but no response is the keyboard or the control IC.

Step 4: Measure

Supply currents

The most informative single measurement is the current drawn from the battery.

Expected supply current

State	Expected	What it means if wrong
Off	~40 µA total (30 µA system board plus ~10 µA power supply quiescent)	Milliamps here means something is leaking. A tired electrolytic on the power board is the usual cause, and it explains batteries flat after weeks in a drawer.
On, processor running	~25 mA	Much higher with no pack activity suggests a rail that is not regulating.
On, processor asleep	~4 mA	Never dropping to this suggests the machine is not entering sleep mode.
Slots active, no devices fitted	~25 mA internally	—
Slots active, peak	up to 170 mA (regulator limit), system peaks 200 mA	—

Use a bench supply at 9 V with the current limit wound down to about 250 mA. A shorted rail then shows up as a limit rather than as damage.

Rail voltages

Supply rails, and what a fault on each looks like

Rail	Off	On	Symptom when missing or wrong
VCC1	3–5 V	5 V ±5 %	Nothing works. If it is present when off but absent when on, the main regulator has failed and the standby regulator is carrying the board.
VCC2	off	5 V ±5 %	Display completely dead although the machine otherwise runs (beeps, responds to keys)
V_LCD	off	adjustable +1.2 V to −3 V by the thumbwheel	No contrast control at all; blank or washed-out display
SVCC	off	5 V ±5 % when the slots are switched on	Packs not recognised at all
SVPP	off	4.5 V normally, 21 V ±2 % pulsed while programming	Packs read fine but SAVE always fails

Two useful behaviours to know:

• The main regulator gives up below about 5.3 V input, after which VCC1 simply follows the supply about 0.3 V below it. A machine that misbehaves on a half-flat battery is behaving as designed.
• LOWBAT is asserted when VCC1 falls about 2 % below nominal. A persistent LOW BATTERY warning with a good cell points at the regulator or the divider chain that feeds the detector, not at the battery.

Symptom table

Psion Organiser II — fault symptoms

Symptom	Likely cause	Action
Completely dead	Flat or high-resistance battery; corroded battery leads; AC key; ON/OFF latch; failed regulator	Known-good alkaline PP3 first. Then check for VCC1 present with the machine off. Then check AC reaches the control IC.
Dead, and the battery goes flat in storage	Leaky electrolytic on the power board	Measure the off-state current. It should be around 40 µA.
Black screen on first switch-on	Contrast at one extreme	Turn the thumbwheel. This is the single most common "fault" reported on these machines.
Display blank but the machine beeps and responds	VCC2 or V_LCD missing	Measure both. VCC2 comes from VCC1 through a switch transistor; V_LCD comes from a charge pump.
No contrast change across the whole wheel travel	V_LCD charge pump or thumbwheel	Check the wheel's resistance changes; if it does, the pump has failed. See the Psion Organiser II Capacitor Replacement Guide.
Missing dots, a dead column, a faded band	Conductive rubber LCD connector strip	Release the LCD clamp, clean both faces and the strip with isopropyl alcohol, reassemble squarely with even pressure. Replace the strip (Psion 3700 0002) if cleaning does not cure it.
Persistent whistle, buzz or squeal — especially on an LZ or LZ64	Ageing electrolytics on the power board. A 10 µF capacitor whose positive side connects to the buzzer is the reported culprit, blocking the pulsing voltage of the programming pump	Recap the power board. This is a documented, confirmed fix.
Clock resets or loses time on every battery change	Hold-up capacitor on the power board	Should hold the rail above 3 V for 2–3 minutes with the machine off.
Clock drifts badly while the machine is off	32768 Hz oscillator marginal, or the stage 2 counter	The machine wakes itself every 34 min 8 s to update the clock; if that mechanism fails the time drifts.
Machine switches itself on in a drawer	Normal	It wakes every 34 min 8 s to keep time, then switches off again.
One key dead	Keymat pill or PCB pad	Clean both. See Psion Organiser II General Maintenance.
A whole row of keys dead	One of the K1–K7 outputs	Those outputs come from the control IC's stage 2 counter bits. Check for a broken track first.
A whole column of keys dead	One of the KBD1–KBD5 inputs on port 5 bits 2–6	Trace the line back to the processor.
AC dead, everything else fine	AC key contact	AC is wired directly to the control IC and to port 5 bit 7, outside the scanned matrix.
Packs read but SAVE always fails	21 V programming pump	The pump storage capacitor is the usual failure. Reads do not use it, which is why the fault is so clean-cut.
Packs not recognised at all	SVCC not switched on; slot contacts; PACON_B	Clean the contacts, then check SVCC appears when a pack operation is attempted.
One slot works, the other does not	Slot contacts or that slot's select path	Swap a known-good pack between slots to confirm before opening anything.
Rampak has lost its contents	Flat backup cell in the pack, or hot-plugging	Check the pack's own cell. Never hot-plug a Rampak.
"DATAPAK FULL" on a pak that looks empty	Erased records still occupy space	Normal EPROM behaviour. Copy the live records to a fresh pak, or have the old one UV-formatted.
Machine shows "PACK?" or "INSERT PACK?" then switches off	It is a POS model	Not a fault. POS machines look for a procedure called BOOT on the fitted packs and switch off if they cannot find one.
Numeric keypad or unusual keyboard legends	POS variant	Confirm with PEEKB(-24).
Persistent LOW BATTERY with a good cell	Regulator or the LOWBAT divider chain	LOWBAT trips at about 2 % below nominal VCC1.
Corrosion on the boards, green vias	Past battery leak or capacitor leakage	Neutralise, clean thoroughly and inspect every track in the affected area. See Battery Explosion, Capacitor or Corrosion Damage.
Buzzer clicks but will not produce a tone	Control IC or software, not the element	The element only makes a sound on transitions of the ALARM signal; a tone is the software toggling it.

Diagnosing the memory configuration

If a machine boots but reports the wrong amount of memory, or crashes in a way that suggests a decoding problem, check the memory decode links. There are eight, arranged as four pairs, and only one of each pair should be fitted.

Correct link options

Version	PROM	RAM	Links fitted
CM	32 KB at $8000–$FFFF	8 KB at $2000–$3FFF	L1, L4, L5, L7
XP	32 KB at $8000–$FFFF	8 KB + 8 KB at $2000–$5FFF	L1, L4, L5, L7
LA	32 KB at $8000–$FFFF	32 KB at $0400–$7FFF	L1, L4, L6, L7

The individual links do the following:

• L1 routes CS1_B to a 32 KB PROM; L2 routes CS2_B to an 8 KB PROM.
• L4 makes A14 available to a 32 KB PROM; L3 pulls PROM pin 27 high when A14 is not needed.
• L6 routes CS6_B to a 32 KB RAM; L5 routes CS5_B to an 8 KB RAM.
• L7 (normally fitted) gates the chip selects with the processor E clock; L8 makes them depend on the address lines alone.

RAM must be 250 ns or better. The 32 KB parts Psion used are 62256LFP / KM62256BLG and the 8 KB parts 6264LFP.

What is realistically repairable

Part	Repairable?	Notes
Power supply board	Yes	Mixed technology, but the electrolytics are leaded and the values are published. This is where most faults are.
LCD connector strip	Yes	Cleaning usually does it; replacements exist (Psion 3700 0002).
LCD panel	Yes, with a donor	Psion part 3900 0003. Note the LZ uses different drivers.
Keymat	Yes	Washable; Psion part 8700 0001.
RAM / PROM	Yes, for SMD-capable hands	62256/6264 static RAM and 27C256/27C64 EPROM are all standard parts, and Organiser II ROM images are archived.
HD6303XFP processor	Difficult	80-pin flat pack. Obtainable but a demanding rework job.
Control IC (µPD65006 / CF70043)	No	Semi-custom parts made only for Psion. A failed control IC means a donor board.
Board with heavy corrosion	Depends	Track repair is possible but the boards are thin and the tracks fine.

Related pages

• Psion Organiser II
• Psion Organiser II General Maintenance
• Psion Organiser II Capacitor Replacement Guide
• Organiser II Spare Parts List
• Psion Organiser Troubleshooting Guide — the Series 1
• Battery Explosion, Capacitor or Corrosion Damage · Capacitor Failure Symptoms