Psion Organiser II Capacitor Replacement Guide

Psion's exploded assembly diagram from the Organiser II Spare Parts List

Capacitor replacement on the Psion Organiser II. Psion's own component-level parts list for the machine survives, so the capacitor values, voltage ratings, physical sizes and Psion part numbers below come from the manufacturer. A published LZ recap confirms the electrolytic values and reports that replacing them cured the LZ's persistent whistle.

In the Spare Parts List all the electrolytics are on the power supply board. The CPU board lists show only chip ceramics (20 pF and 100 nF), so the CPU board is not a recap candidate.

Visual inspection and failure signs

Recap when there is evidence:

• A whistle, buzz or squeal from the machine, especially an LZ or LZ64. The Byte-My-Vdu author cured this with a recap.
• The clock or internal memory is lost on a quick battery change with the machine off. Psion allows 90 seconds for a battery change; the Technical Manual's design hold-up is two to three minutes above 3 V.
• Datapaks read but will not write. Only writing uses the 21 V programming pump and its storage capacitor.
• No usable contrast range from the thumbwheel.
• Batteries go flat in storage. Standby draw should be about 40 µA in total.
• Any visible leakage or corrosion. After his recap the Byte-My-Vdu author advises changing all the electrolytics, because leaking electrolyte corrodes the board.

Organiser II capacitor list

Designators

The 1986 Technical Manual and the later Spare Parts List describe two different power supply board designs. The Technical Manual's board uses discrete transistors (TR1 to TR16), a 9491BJ reference diode at RD1 and a zener at ZN1, and it describes C1, C3, C6 and C8 as the V_LCD storage, VCC1 hold-up, pump storage and V_LCD series capacitors. The board in the Spare Parts List has a REF 308 reference at IC2, HEF4011 and HEF4093 logic at IC3 and IC4 and zeners at ZD1 and ZD2; it assigns C1, C2, C3, C12 and C13 to chip ceramics and puts the electrolytics at C5–C11 and C15. A designator therefore does not mean the same part in both documents, and the tables below are for the Spare Parts List board. If a board has RD1 and ZN1 and no IC2 or ZD1, it follows the Technical Manual's design and the list does not apply to it. Work from the parts on the board.

Power supply board electrolytics

From Psion's parts list for the power supply board, "ORG PSU HAND ASSY" (Psion part 2000 0230, PARESA 1008002201):

Organiser II power supply board: electrolytic capacitors

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

That is two axial and six radial electrolytics, eight in all.

Ceramics and trimmer

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

Leave the C14 trimmer alone.

Other parts on the board

Semiconductors and controls on the power supply board

Designator	Part
IC1	LM324D quad op-amp (SO14)
IC2	TSC04 REF 308 voltage reference
IC3, IC4	HEF4011UBT quad NAND, HEF4093BT quad Schmitt NAND
ZD1	BZX84C 33 V zener
ZD2	BZV49C 15 V zener
TR9, TR12	BCX51 PNP (SOT89)
VR1	10 kΩ potentiometer (contrast thumbwheel)
X1	32.768 kHz crystal (TC-38)
	Interboard connector, 27-way (4700 0004)

ZD1's 33 V matches the zener voltage the Technical Manual gives for the programming pump's READY feedback.

LZ cross-check

The Byte-My-Vdu LZ recap counted nine electrolytics, seven radial and two large axial, and listed the radials it removed as five 10 µF 25 V, one 1 µF 50 V and one 100 µF 6.3 V. The 10 µF and 1 µF parts agree with Psion's list (C6, C8, C10, C11, C15 and C9), and the two axials correspond to C5 and C7. The 100 µF 6.3 V radial is not in Psion's power supply board list, so the LZ board carries at least one position the list does not cover. Count and read the parts on the board before ordering.

What the capacitors do

The Technical Manual describes these functions for the power supply circuit:

Power supply capacitor functions (Technical Manual chapter 3)

Function	Technical Manual description	Symptom when it fails
VCC1 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 supply is removed	Clock and internal memory lost on a 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 +1.2 V and −3 V	Weak contrast range
Programming pump storage capacitor	Charged to about 35 V through a 1 mH inductor, then regulated to 21 V; holds 21 V for 50 ms at 50 mA, enough to program one EPROM byte	Datapaks read but SAVE fails

The Technical Manual also uses the ALARM (buzzer) signal as an interlock on the 21 V programming regulator. On the LZ whistle, a commenter on the Byte-My-Vdu recap identifies the cause as one of the 10 µF capacitors whose positive side connects to the buzzer, which blocks the pulsing voltage of the pump when it degrades.

Capacitor replacement procedure

The route in follows the Byte-My-Vdu LZ recap.

1. Remove the battery and all packs, after backing up the internal memory to a Datapak.
2. Remove the case screws and open the machine. The main board is screwed to the front half of the case.
3. Lay the machine face down and remove the single screw holding the top board.
4. The main logic board is still joined to the keyboard by a stiff ribbon cable behind the pack slot pins. Ease the logic board up gently, far enough to reach the screws holding the keyboard PCB to the front case.
5. Record every capacitor's value, voltage and polarity before removing it, checked against the tables above and the silkscreen.
6. Add fresh flux and a little fresh solder to each joint.
7. Lift one lead at a time with the joint fully molten, then clear the hole with wick.
8. Fit the replacement the correct way round, solder and trim.
9. Inspect for splashes and bridges before reassembly.

The rest of the power supply board is surface-mount, so use a fine tip and keep heat away from the neighbouring chip parts.

Recommended tools and parts

• 105 °C aluminium electrolytics of the same capacitance and the same or higher voltage rating.
• C7 is rated 40 V; the programming pump's storage capacitor charges to about 35 V. Never fit a lower-rated part in the C7 position; 50 V gives more margin.
• Match the form factor. C5 and C7 are axial; the others are radial and small (5 × 5 mm and 5 × 4 mm). Check the datasheet dimensions against the space under the case before ordering. If radials go into the axial positions, form and sleeve the leads so that nothing can touch an adjacent track.
• Low-ESR parts for the charge-pump positions.
• A temperature-controlled, earthed soldering iron with a fine tip, solder wick, flux and leaded solder.
• An ESR or capacitance meter.

See Recommended Tools for the general workshop kit.

Post-recap checks

1. Power the machine first from a bench supply set to 9 V with the current limit at 100 mA.
2. Check that the standby current with the machine off is back to about 40 µA.
3. Switch on and check that the running current is about 25 mA, falling to about 4 mA when the processor sleeps.
4. Sweep the thumbwheel and check for a full contrast range.
5. Set the clock, switch off, and disconnect the battery for no more than a minute (Psion allows 90 seconds). The time should survive.
6. SAVE a record to a Datapak. Writing is the only test that exercises the 21 V programming pump.
7. Listen for the whistle.
8. Check the buzzer with BEEP from OPL or by setting an alarm.

If a function that worked before the recap has stopped, check the polarity of every replaced part first.

Related pages

• Psion Organiser II
• Psion Organiser II General Maintenance
• Psion Organiser II Troubleshooting Guide
• Psion Organiser II Spare Parts List
• Psion Organiser Capacitor Replacement Guide
• Capacitor Failure Symptoms
• Recommended Tools