Josh: Create Psion page set: researched from Psion manuals, service documentation and community repair sources

2026-09-08T22:16:17Z

Create Psion page set: researched from Psion manuals, service documentation and community repair sources

New page

<templatestyles src="Template:StyledTable/styles.css" />
[[File:Psion Organiser II exploded view.png|thumb|420px|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.<ref name="spares">''Psion Organiser II Spare Parts List v3'', Psion. Hosted on this wiki as [[:File:Psion Organiser II Spare Parts List v3.pdf]]. Source for every value, designator, physical size and Psion part number in the tables on this page.</ref> A community teardown of an LZ independently confirms the electrolytic values.<ref name="bmv">Byte-My-Vdu, [https://bytemyvdu.wordpress.com/2018/12/14/psion-ii-lz-repair/ "Psion II LZ Repair"], 14 December 2018, and the comments beneath it. Source for the LZ's nine electrolytics, the measured radial values, the whistling symptom, the confirmation that a recap cures it, and Ralf Rosche's identification of the 10 µF capacitor connected to the buzzer as the culprit.</ref>

== 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.<ref name="spares" />

== ⚠️ 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.<ref name="bmv" /> 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.<ref name="bmv" /> 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.<ref name="tech3">''Psion Organiser II Technical Manual'', Psion Ltd, 1986, Chapter 3 "Power Supply Board", transcribed at [https://www.jaapsch.net/psion/tech03.htm Jaap's Psion Organiser II Page]. Source for the function of each capacitor position, the rail voltages, the 2–3 minute hold-up figure, the 21 V programming pump behaviour and the ALARM/SVPP interlock.</ref>

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.<ref name="tech3" />
* '''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.<ref name="tech3" />
* '''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."<ref name="bmv" />

== Power supply board — full capacitor list ==

From Psion's parts list for the '''ORG PSU HAND ASSY (Psion part 2000 0230 / PARESA 1008002201)'''.<ref name="spares" />

=== Electrolytics — the recap targets ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Organiser II power supply board — electrolytic capacitors'''<ref name="spares" />
! 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 ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Organiser II power supply board — ceramic and trimmer capacitors'''<ref name="spares" />
! 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 ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Key active components on the power supply board'''<ref name="spares" />
! 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:<ref name="bmv" />

* '''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:<ref name="tech3" />

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Functional roles, and the symptom when each degrades'''<ref name="tech3" />
! 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<ref name="bmv" />
|}

== 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.<ref name="bmv" />

# '''Remove the battery''' and all packs.
# Remove the case screws and open the machine. The motherboard is screwed to the front half of the case.
# '''Lay the machine face down''' and unscrew the top board, which is held by '''a single screw'''.
# 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.
# Turn the boards over. '''Handle both with care'''; they are forty years old and thin.
# '''Record every capacitor's value, voltage and polarity before removing it''', cross-checked against the tables above and the silkscreen.
# Add fresh flux and a little fresh solder to each joint and let it mix with the old solder.
# '''Lift one lead at a time with the joint fully molten''', then clear the hole with wick.
# Fit the replacement the correct way round; solder and trim.
# '''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 ==

# Fit a fresh PP3 — ideally through a bench supply set to 9 V with the current limit at 100 mA first.
# '''Check the standby current''' is back down to the order of 40 µA with the machine off.<ref name="tech3" />
# Switch on and confirm the running current is around 25 mA, dropping to about 4 mA when the processor sleeps.<ref name="tech3" />
# '''Sweep the thumbwheel''' and confirm a full contrast range.
# '''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.
# '''SAVE a record to a Datapak.''' Writing is the only test that exercises the 21 V programming pump.
# '''Listen.''' The whistle should be gone.
# Check the buzzer still works — <code>BEEP</code> 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]]

== References ==

<references />

{{Navbox-Psion}}

[[Category:Psion]]
[[Category:Capacitor Replacement Guides]]

Psion Organiser II Capacitor Replacement Guide - Revision history

Josh: Create Psion page set: researched from Psion manuals, service documentation and community repair sources