Psion Organiser II Capacitor Replacement Guide

Psion's exploded assembly diagram from the Organiser II Spare Parts List. The full parts list, including every capacitor value below, is hosted here as File:Psion Organiser II Spare Parts List v3.pdf.

Capacitor work on the Psion Organiser II.

Unusually for a machine of this age, Psion's own component-level parts list survives, so the capacitor values, voltages, physical sizes and Psion part numbers are all documented rather than guessed. A community teardown of an LZ independently confirms the electrolytic values.

The one thing to know first

All the electrolytics in an Organiser II are on the power supply board. The CPU board carries nothing but chip ceramics — 20 pF crystal load capacitors and 100 nF decoupling — and is not a recap candidate.

⚠️ Designator warning

The 1986 Technical Manual and the later Spare Parts List use different designator sets for the power supply board. The Technical Manual describes C1, C3, C6 and C8 doing particular jobs; the parts list assigns C1, C2, C3, C12, C13 to chip ceramics and puts the electrolytics at C5, C6, C7, C8, C9, C10, C11 and C15.

"C3" therefore does not mean the same thing in both documents. Work from the physical part on your own board, not from the letter alone.

Is the Organiser II a recap candidate?

Yes — and the LZ and LZ64 more than most.

The best-known symptom is a persistent, irritating whistle or buzz from an LZ or LZ64. It is caused by ageing electrolytics, and a recap cures it. A commenter on that teardown narrowed it further: one of the 10 µF capacitors, whose positive side connects to the buzzer, blocks the pulsing voltage of the voltage pump when it degrades. That fits the documented circuit — Psion used the ALARM (buzzer) signal as an interlock in the programming-voltage path, so the buzzer and the pump genuinely do share circuitry.

Recap when there is evidence:

• A whistle, buzz or squeal from the machine — the classic LZ/LZ64 fault.
• The clock loses time, or resets, when the battery is changed. The hold-up capacitor should keep the logic rail above 3 V for two to three minutes with the battery out, provided the machine is off.
• Datapaks read but will not write. The 21 V programming pump depends on a storage capacitor; reads do not touch it.
• No usable contrast range from the thumbwheel.
• Batteries flat after a short time in a drawer. Standby draw should be around 40 µA in total.
• Any visible leakage. The teardown author's advice after thirty years is blunt: change them all, because "the acid will leak out and corrode the PCB or you have the vapour latching on to everything."

Power supply board — full capacitor list

From Psion's parts list for the ORG PSU HAND ASSY (Psion part 2000 0230 / PARESA 1008002201).

Electrolytics — the recap targets

Organiser II power supply board — electrolytic capacitors

Designator	Value	Rating	Type and size	Psion part no.
C5	470 µF	16 V	Electrolytic, axial, 20 × 8 mm	4201 0002
C7	100 µF	40 V	Electrolytic, axial, 16 × 8 mm	4201 0001
C6, C8, C10, C11, C15	10 µF	25 V	Electrolytic, radial, 5 × 5 mm	4202 0002
C9	1 µF	50 V	Electrolytic, radial, 5 × 4 mm	4202 0003

That is two axial and six radial electrolytics — eight in total.

Ceramics and the trimmer — normally left alone

Organiser II power supply board — ceramic and trimmer capacitors

Designator	Value	Tolerance	Package	Psion part no.
C1, C2	220 pF	5 %	Chip 1206	3200 0015
C3	100 nF	20 %	Chip 1206	3200 0008
C12	12 pF	5 %	Chip 1206	3200 0003
C13	27 pF	5 %	Chip 1206	3200 0018
C14	11–60 pF trimmer	—	Trimmer	4205 0002

Do not disturb C14. It is a trimmer and it was set at the factory.

Other parts on the same board, for orientation

Key active components on the power supply board

Designator	Device	Role
IC1	LM324D (SO14)	Quad op-amp — the regulator error amplifiers
IC2	TSC04 REF 308	Voltage reference
IC3, IC4	HEF4011UBT (quad NAND), HEF4093BT (quad Schmitt NAND)	Control logic
ZD1	BZX84C 33 V zener	Sets the programming-pump READY threshold
ZD2	BZV49C 15 V zener	—
TR9, TR12	BCX51 PNP (SOT89)	Pass transistors
VR1	10 kΩ potentiometer	Contrast thumbwheel
X1	32.768 kHz crystal (TC-38)	Real-time clock oscillator
—	CONNECTOR INTRBRD 27 WAY (4700 0004)	The board-to-board strip connector

Community cross-check: the LZ teardown

A published LZ recap counted nine electrolytics — seven radial and two large axial — and measured the radials as:

• 5 × 10 µF 25 V
• 1 × 1.0 µF 50 V
• 1 × 100 µF 6.3 V

The first two agree exactly with Psion's parts list (C6/C8/C10/C11/C15 and C9). The two large axials correspond to C5 (470 µF) and C7 (100 µF).

The 100 µF 6.3 V radial is not in the parts list above, which covers the PSU "hand assembly". Either the LZ board carries an extra position, or it differs in revision. Count and measure the parts on your own board before ordering — do not assume either list is complete for your machine.

What each capacitor does

Psion's Technical Manual describes the circuit functionally. Mapped onto the physical parts, the electrolytics do the following:

Functional roles, and the symptom when each degrades

Function	What it does	Symptom when it fails
Logic rail decoupling and hold-up	Decouples the always-on VCC1 rail, and with the machine off holds it above 3 V for 2–3 minutes after the battery is removed	Clock resets and RAM is lost on every battery change
V_LCD pump series capacitor	Passes the 1024 Hz square wave through the thumbwheel into the contrast charge pump	No contrast control; blank or washed-out display
V_LCD storage capacitor	Holds the negative display rail, adjustable between about +1.2 V and −3 V	Weak, drifting or temperature-dependent contrast
Programming pump storage capacitor	Charged towards 35 V through a 1 mH inductor, then regulated to 21 V. Must hold 21 V for 50 ms at 50 mA — enough for one EPROM byte	Datapaks read but SAVE always fails
Buzzer-coupled 10 µF	Sits on the ALARM path, which is also an interlock for the programming voltage	The LZ/LZ64 whistle, and pump misbehaviour

Choosing replacements

• 105 °C aluminium electrolytics, equal capacitance, equal or higher voltage.
• C7 must be rated well above 35 V. Psion fitted a 40 V part because the programming pump charges its storage capacitor towards 35 V. A 25 V part here will fail. If in doubt fit 50 V.
• Match the form factor. C5 and C7 are axial; the rest are radial and physically tiny (5 × 5 mm and 5 × 4 mm). There is very little room under the case, so ordering a physically larger modern part is a real risk — check the datasheet dimensions.
• Axial parts are still made. If you fit radials in the axial positions, form and sleeve the leads so nothing can short to an adjacent track.
• Low-ESR parts are worth using in the charge-pump positions, where switching current rather than bulk capacitance is what matters.
• The original tolerances are wide; modern ±20 % parts are comfortably within specification.

Replacement procedure

The LZ teardown gives the practical route in.

1. Remove the battery and all packs.
2. Remove the case screws and open the machine. The motherboard is screwed to the front half of the case.
3. Lay the machine face down and unscrew the top board, which is held by a single screw.
4. The main logic board is still connected to the keyboard by a ribbon cable behind the ROM slot pins. That cable is stiff; ease the logic board up gently — do not force it — far enough to reach the screws holding the keyboard PCB to the front case.
5. Turn the boards over. Handle both with care; they are forty years old and thin.
6. Record every capacitor's value, voltage and polarity before removing it, cross-checked against the tables above and the silkscreen.
7. Add fresh flux and a little fresh solder to each joint and let it mix with the old solder.
8. Lift one lead at a time with the joint fully molten, then clear the hole with wick.
9. Fit the replacement the correct way round; solder and trim.
10. Inspect for splatter and bridges before reassembly. Hairline bridges measure a few ohms and produce very misleading faults.

Use a low-power, earthed, temperature-controlled iron. Everything else on this board is surface-mount and does not appreciate a large tip nearby.

Post-recap verification

1. Fit a fresh PP3 — ideally through a bench supply set to 9 V with the current limit at 100 mA first.
2. Check the standby current is back down to the order of 40 µA with the machine off.
3. Switch on and confirm the running current is around 25 mA, dropping to about 4 mA when the processor sleeps.
4. Sweep the thumbwheel and confirm a full contrast range.
5. Set the clock, switch off, remove the battery for a minute, refit it. The time should survive — the hold-up is specified at two to three minutes.
6. SAVE a record to a Datapak. Writing is the only test that exercises the 21 V programming pump.
7. Listen. The whistle should be gone.
8. Check the buzzer still works — BEEP from OPL, or set an alarm.

If a function that worked before the recap has stopped, check the polarity of every part you replaced before looking anywhere else.

Related pages

• Psion Organiser II
• Psion Organiser II General Maintenance
• Psion Organiser II Troubleshooting Guide
• Psion Organiser Capacitor Replacement Guide — the Series 1, for which no values were ever published
• Capacitor Failure Symptoms · Recommended Tools