Psion Organiser Capacitor Replacement Guide

The Series 1. Every electrolytic in the machine is on the through-hole power board, which makes this one of the easier recaps in the Psion range — once you have worked out what the values are.

Capacitor work on the Psion Organiser (Series 1, 1984).

Read this first. Psion never published a schematic, a parts list or a service manual for the Series 1. There is therefore no authoritative list of capacitor values for this machine, and this page does not invent one. What it does give you is: where the capacitors are, what the designators are, what each functional block does, how to work out the values from your own board, and what the symptoms of each failure look like.

Where the capacitors are

The Organiser is built as two boards.

Board	Construction	Capacitors
"PSION PROCESSOR"	Surface-mount: HD6301X0F CPU, HD44780A00H LCD controller, HEF-series CMOS glue logic, two crystals	Chip ceramics only — crystal load capacitors and supply decoupling. Not a recap candidate.
"PSION POWER"	Through-hole leaded: LM324N at IC1, TO-92 transistors, quarter-watt resistors, VR1 contrast thumbwheel, RD1 reference diode, ZN1 zener	All the electrolytics in the machine. Designators visible on the silkscreen include C1, C3, C5, C6, C8, C9 and C10.

This split is good news: the parts that age are all on the leaded board, and leaded parts are easy to desolder, easy to measure and easy to buy.

What each capacitor does

Psion documented the Organiser II power supply board in detail, and that board uses the same designator scheme and the same LM324-plus-reference-diode topology as the Series 1 board. The functional blocks below are therefore a strong guide to what the Series 1 parts are for — but verify against your own board before replacing anything.

Functional blocks on the Organiser II power board, applied by analogy to the Series 1

Designator (Organiser II)	Function	Failure symptom on a Series 1
C3	Decouples the always-on logic rail and, with the machine off, holds that rail above 3 V for two to three minutes after the battery is removed	The clock resets to 1 January on every battery change; RAM contents lost during a battery swap
C8	Series capacitor in the display-contrast charge pump, driven from a 1024 Hz square wave through the thumbwheel	No contrast control at all; blank or washed-out display that does not respond to the wheel
C1	Storage capacitor for the negative display rail (V_LCD), nominally adjustable between about +1.2 V and −3 V	Weak or drifting contrast; display fades as the machine warms up
C6	Storage capacitor in the Datapak programming voltage pump. Charged towards 35 V through an inductor, then regulated to 21 V and applied in pulses. Must hold 21 V for 50 ms at 50 mA	Datapaks read normally but SAVE always fails. The classic signature

Note that the Organiser II's electrolytics are the higher-numbered designators on its power board (C5, C6, C7, C8, C9, C10, C11, C15 in Psion's own parts list), while C1, C2, C3, C12, C13 are chip ceramics. The Series 1 board is leaded throughout, so the mapping is not one-to-one. Read your own board.

Working out the values

Because no list exists, the values have to come from the parts themselves.

1. Photograph the board before touching it, square-on and in good light, so you can recover the original layout and polarity.
2. Read the printing on each electrolytic. Forty-year-old parts are usually still legible: value in µF, working voltage, and often a temperature rating. Note the physical size too, because the replacement has to fit the same hole spacing and the same clearance under the case.
3. Record polarity — both from the part and from the "+" mark on the silkscreen, which the Series 1 board does carry.
4. Measure each part out of circuit with an ESR/capacitance meter. In-circuit readings on a board with an LM324 and several transistors across the rails are not trustworthy.
5. Note the lead pitch before you order.

Build a table for your own machine as you go. If you do this, please consider contributing it — a verified Series 1 capacitor list does not currently exist anywhere public.

Is a recap justified?

The Series 1 is not a machine with a known capacitor plague, and there is no community tradition of recapping them on sight. Recap when there is evidence:

• Visibly failed parts — bulging, weeping, crusty residue around the base, or a cracked sleeve.
• The clock resets on every battery change. The machine should ride out about fifteen seconds without a battery; the underlying hold-up is specified at two to three minutes on the sister design. If it cannot manage fifteen seconds, the hold-up capacitor is finished.
• Datapaks read but will not write. The programming voltage pump depends on a storage capacitor; reads do not use it at all, which is why the fault is so clean-cut.
• No usable contrast range from the thumbwheel, with the wheel itself proven good.
• Batteries flat after a few weeks in a drawer. With the machine off the supply current should be of the order of 20 µA; anything in the milliamps means something is leaking.
• Any sign of electrolyte on the board. Once it has escaped, it keeps corroding.

If none of those apply, leave it alone.

Choosing replacements

• 105 °C aluminium electrolytics, equal capacitance, equal or higher voltage rating. The machine runs from a 9 V PP3, so most parts will be low-voltage — but the programming-pump storage capacitor sees roughly 35 V and must be rated well above that. Do not fit a low-voltage part there.
• Match the physical size. There is very little headroom under the case; a modern part is usually smaller than the original, which is fine, but check before ordering.
• Match the lead pitch, or form the leads carefully and sleeve them.
• Modern ±20 % parts are comfortably inside the tolerance these circuits were designed around.
• Consider low-ESR parts for the charge-pump positions, where switching current is what matters.

Replacement procedure

1. Remove the battery and both Datapaks.
2. Slide off the protective cover, open the case and separate the power board, noting the ribbon and pin-header orientation.
3. Record each capacitor's value, voltage and polarity before removing it, cross-checked against the silkscreen "+" marks.
4. Work on a supported board. Add fresh flux and a little fresh solder to each joint and let it mix with the old solder before removing anything.
5. Lift one lead at a time with the joint fully molten, then clear the hole with wick. The board is single-thickness and the pads will lift if you fight them.
6. Fit the replacement the correct way round; solder and trim.
7. Inspect for splatter and bridges before reassembly — a hairline bridge measuring a few ohms produces very misleading faults.

Use a low-power, earthed, temperature-controlled iron. Nothing on this board needs a large tip.

Post-recap verification

1. Fit a fresh PP3 — ideally via a bench supply set to 9 V with the current limit at about 100 mA first, so a mistake shows up as a limit rather than as smoke.
2. Confirm the off-state current is back in the tens of microamps.
3. Switch on and check the display appears and that the thumbwheel gives a full contrast range.
4. Set the clock, switch off, remove the battery for twenty seconds, refit it — the time should survive.
5. Test SAVE and FIND on both slots with a known-good pak. Writing is the test that exercises the programming voltage pump.
6. Leave it switched off for a week and check the clock is still right and the battery has not drained.

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

Related pages

• Psion Organiser
• Psion Organiser General Maintenance
• Psion Organiser Troubleshooting Guide
• Psion Organiser II Capacitor Replacement Guide — the successor, for which Psion did publish values
• Capacitor Failure Symptoms · Recommended Tools