Psion Organiser Capacitor Replacement Guide

The Psion Organiser Series 1

Capacitor replacement on the Psion Organiser (Series 1, 1984). Psion published no schematic, parts list or service manual for the Series 1, so there is no manufacturer's list of capacitor values. Every electrolytic in the machine is on the through-hole power supply board; the values have to be read from the parts on the board being worked on.

Visual inspection and failure signs

Recap when there is evidence of a problem:

• Bulging, weeping or crusted residue around the base of a capacitor, or a split sleeve.
• Electrolyte on the board. It keeps corroding tracks and leads after it has escaped; see Battery Explosion, Capacitor or Corrosion Damage.
• The clock is lost on a quick battery change. Psion specifies fifteen seconds of clock hold-up with the machine switched off.
• Datapaks read but will not write. Only writing uses the programming-voltage pump and its storage capacitor.
• No usable contrast range from the thumbwheel, with the wheel itself proven good.
• Batteries go flat in storage. With the machine off, the supply should draw about 22 µA (Psion's 0.2 mW at 9 V); milliamps with the machine off means something is leaking.

Capacitor locations

The Organiser is built as two boards.

Psion Organiser Series 1 boards

Board	Construction	Capacitors
"PSION PROCESSOR"	Surface-mount: HD6301X0F CPU, HD44780A00H LCD controller, HEF-series CMOS glue logic, two crystals	Chip ceramics only
"PSION POWER SUPPLY ISS 2"	Through-hole: LM324N at IC1, BC548 transistors, leaded resistors, VR1 contrast thumbwheel, RD1 reference diode, ZN1 zener	All the electrolytics. Designators visible on the silkscreen include C1, C3, C5, C6, C8, C9 and C10.

What each position does

Psion documented the Organiser II power supply board in its 1986 Technical Manual. That board uses the same scheme as the Series 1 board: an LM324 regulator referenced to RD1, a zener ZN1 in the programming pump, the VR1 thumbwheel, and capacitors at C1, C3, C6 and C8. The table gives the Organiser II functions as a guide to the Series 1 parts with the same designators. Confirm each on the board before replacing anything.

Organiser II power supply capacitor functions (Technical Manual chapter 3)

Designator	Function on the Organiser II	Likely symptom if it fails
C3	Decouples the always-on logic rail (VCC1); with the machine off, holds that rail above 3 V for two to three minutes after the supply is removed	Clock lost on every battery change
C8	Series capacitor in the display-contrast charge pump, driven by a 1024 Hz square wave through the thumbwheel	No contrast control; blank or washed-out display that does not respond to the wheel
C1	Storage capacitor for the negative display rail (V_LCD), adjustable between +1.2 V and −3 V	Weak contrast range
C6	Storage capacitor in the Datapak programming pump: charged to about 35 V through inductor L1, then regulated to 21 V and applied in pulses; holds 21 V for 50 ms at a 50 mA load	Datapaks read normally but SAVE fails

Designators do not carry across reliably between boards. The later surface-mount Organiser II power supply board in Psion's Spare Parts List v3 has its electrolytics at C5–C11 and C15, chip ceramics at C1–C3, C12 and C13, and a 33 V zener at ZD1 in place of ZN1.

Recording the values

1. Photograph the board square-on in good light before touching it, so the layout and polarity can be recovered.
2. Read the printing on each electrolytic: capacitance, working voltage and any temperature rating. Note the physical size and lead pitch too, because the replacement has to fit the same holes and the same clearance under the case.
3. Record the polarity from both the part and the "+" mark on the silkscreen.
4. Measure each part out of circuit with an ESR or capacitance meter. In-circuit readings on this board are unreliable because the LM324 and several transistors sit across the rails.

Capacitor replacement procedure

1. Remove the battery and both Datapaks.
2. Slide off the protective cover, remove the screws in the back of the case and lift the board assembly out. Note the orientation of the ribbon cable and the pin headers joining the two boards before separating them.
3. Record each capacitor's value, voltage and polarity before removing it, checked against the silkscreen "+" marks.
4. Support the board. Add fresh flux and a little fresh solder to each joint before removing anything.
5. Lift one lead at a time with the joint fully molten, then clear the hole with wick. Do not force a lead: the pads lift easily on an old board.
6. Fit the replacement the correct way round, solder and trim.
7. Inspect for splashes and bridges before reassembly.

Recommended tools and parts

• 105 °C aluminium electrolytics of the same capacitance and the same or higher voltage rating. The machine runs from a 9 V PP3, but the programming-pump storage capacitor runs well above the battery voltage: on the Organiser II it charges to about 35 V. Never fit a part rated lower than the original in that position.
• Replacements of the same or smaller size and matching lead pitch, or with the leads formed carefully and sleeved.
• 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 about 100 mA, so a mistake shows up as the current limit rather than as damage.
2. Check that the off-state current is back in the tens of microamps.
3. Switch on and check that the display appears and the thumbwheel gives a full contrast range.
4. Set the clock, switch off, and disconnect the battery for about ten seconds, well inside Psion's fifteen-second hold-up. The time should survive.
5. Test SAVE and FIND on both slots with a known-good pak. SAVE exercises the programming-voltage pump.
6. Leave the machine switched off for a week, then check that 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 replaced part first.

Related pages

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