Psion Series 3a Troubleshooting Guide

Psion Series 3a

The Psion Series 3a (1993) is well documented for repair. Psion's Series 3a Service Manual has a fault table, disassembly instructions and the factory test limits for current consumption, and the SIBO Hardware Reference describes the power states and supply rails. Most faults are mechanical: the lead from the battery contacts, the button-bar cable, the screen cable and the hinges. The same faults occur on the Psion Series 3, Psion Series 3c and Psion Series 3mx; differences are noted below.

Preliminary and power-up checks

Back up the internal disk if the machine still works. Removing the main cells and the backup cell together erases the internal memory. Work on an earthed mat with a wrist strap. Before dismantling anything, Psion's manual says to check for a broken warranty label and for corrosion, and to test peripherals (SSDs, links, power supplies, batteries) in a Series 3a that is known to work, because they cause faults of their own.

1. If the screen is blank, change the contrast with Psion-> and Psion-< before anything else.
2. Fit fresh alkaline AA cells. Some brands are shorter than others and make poor contact, which gives false low-battery warnings; NiCd cells give a short running time, which can look like a fault.
3. If the machine appears dead, listen for key clicks. The main board may be working behind a dead LCD.
4. If it has crashed, do a soft reset: press an unfolded paper clip into the reset hole above the On/Esc key. A hard reset (hold the right Shift key while resetting and pressing On/Esc) erases the internal memory. Psion advises fully testing a machine that has crashed, because an intermittent hardware fault can cause a crash.

Psion's fault table

Series 3a fault table from Psion's service manual

Symptom	Probable cause	Action
Unit appears dead	Main board, LCD or daughter board	Check the batteries or DC supply. Listen for key clicks. Test the main board with another LCD and daughter board
Dead on main batteries	Flat cells, battery cable, main board	Replace the cells, then the battery cable, then the main board
Membrane (application) keys not responding	Membrane, daughter board, main board	Replace in that order
Keys not working	Split keymat, membrane, main board	Replace in that order
No sound or incorrect sound	Daughter board, main board	Replace in that order
LCD lines missing	LCD	Replace the LCD module
Cannot write to a Flash SSD	Daughter board, main board	Replace in that order
SSDs not read	SSD, door switch, daughter board, main board	Check that the file lists update when a door is closed (a door switch may be out of place), then replace the daughter board, then the main board
Expansion port not recognised	Expansion door switch, main board	Check that the switch contact is in place and working, then replace the main board
Unit constantly resets	Main board	Replace the main board

Power and battery faults

Power states

A SIBO machine has four power states.

SIBO power states

State	Description
Standby	The normal "off" state. The main oscillator and the processor are shut down; the system chip and the memory stay powered and the real-time clock runs
Backup	Exists only when the main supply has failed or is absent. As standby, but Vcc1 comes from the backup cell and switching to the operating state is inhibited
Idle	The processor is powered and the oscillator runs, but the processor clock is stopped until an interrupt arrives
Operating	Everything running

A machine in the backup state keeps its memory but will not switch on. A broken battery lead has the same effect as removing the cells: the machine stays in the backup state until the main supply reaches the board again.

Battery warnings and the battery lead

Symptom	Probable cause	Action
Low-battery warnings or switch-off with fresh cells	Poor contact at the battery terminals	Clean the contacts; try a longer brand of cell
Warnings, switch-off or failure to turn on that change as the lid moves	Broken wires in the battery lead	Re-seat the two-pin connector; replace the wires
Alarms replaced by short beeps	Main cells too low to play digital sounds	Fresh cells, then check the contacts and lead
"Replace backup battery" with a good cell	Poor contact at the backup cell	A small piece of paper behind the cell, clear of the contact, has cured this
Time lost when the main cells are changed	Fault on a 3a, which has a hardware real-time clock in ASIC9; normal on a Series 3	Check the backup cell and its contacts

The battery lead runs from the contacts in the battery housing to a two-pin connector on the main board, and flexes every time the lid is opened and closed. The comp.sys.psion FAQ called its failure the "dreaded battery lead problem", the most common battery fault on these machines.

1. Back up, then remove the main cells and the backup cell.
2. Remove the battery cover and the four screws holding the battery housing.
3. Lift the housing away, pull the heat-sleeved part of the cable out of its retaining clip and unplug the connector gently with pliers.
4. Re-seat the connector and test. This alone sometimes cures the fault.
5. If it does not, fit new wires. Psion recommended always replacing the battery wires when a machine was dismantled.

Tony Rosser rebuilt the lead with an RS Components 2-way housing (RS 279-9156) and crimp leads (RS 279-9516). Sven Killig later found that the housing fits well enough but that the crimp lead is too short for the longer wire, and used RS 279-9443, which is twice the length. When refitting, Psion's routing starts at the left-hand (longer) wire, runs through the moulding details and cable grips with no slack, passes around the screw boss and under the right-hand contact, and includes a clip-in ferrite bead; the wires should leave close to the connector at 90°.

Current consumption

Psion's final test measured current through the battery terminals, and gives these maximums.

Series 3 and 3a maximum current (Psion final test)

Model	Standby	On and idle
Series 3	0.250 mA	20.0 mA
Series 3a, 256 KB or 512 KB	0.205 mA (typical 0.155 mA)	27.0 mA (typical 22 mA)
Series 3a, 1 MB	0.245 mA (typical 0.190 mA)	32 mA (typical 27 mA)
Series 3a, 2 MB	0.310 mA (typical 0.250 mA)	40 mA (typical 35 mA)

The test applies 2.75 V to a Series 3a for the standby measurement, and 2.5–2.6 V with a 500 mA limit while the machine is operating. The on-and-idle reading is taken at the end of the test sequence, with the processor inactive. A standby current well above the limit drains the cells while the machine is switched off.

Display faults

Symptom	Probable cause	Action
Blank or very dark screen	Contrast out of range	Psion-> and Psion-<
Vertical lines ("jail bars")	Cracks in the cable to the screen, or a poor joint where it enters the screen	See below
Rows or columns of pixels missing	LCD module	Replace the LCD module
Dark pixels, lines or patches that stay on	LCD fault	Replace the LCD module

MacKay found that his jail bars came and went with the bend in the cable where it enters the screen, and that the lines cleared when the cable was straight. With the battery housing removed and the lid half open, he taped strips of old plastic card to both sides of the cable at that point to stop it bending. The lines were much reduced but did not disappear. The permanent fix is a replacement LCD module or a donor lid; the separation procedure is in Psion Series 3a Hinge Repair.

When fitting a replacement LCD module, match its bias polarity to the main board. Boards before revision 4.0 take only negative-bias modules; later boards are built for one or the other, and positive-bias boards have a "+" in their serial number. A negative-bias module on a positive-bias board is damaged. Seiko TAB modules are positive bias and Hitachi TAB modules negative.

Keyboard and button bar

The eight application buttons are on a membrane in the button bar, joined to the lower (daughter) board by a thin blue ribbon cable. After a knock the cable can come out of its connector, and the whole button bar stops working. The fix published in the FAQ, by Kevin Reilly:

1. Back up, and remove the SSDs and batteries.
2. Remove the four screws in the battery compartment and unplug the battery lead; remove the two screws inside the SSD doors.
3. Open the machine, taking care not to trap the button bar, and remove the keyboard cover (the keyframe) and the rubber keymat.
4. Lift the keyboard board out, front edge first, at about 40°. The comms port cover may need pressing in to release it.
5. Near the middle front of the lower board, push the locks on the blue cable's connector forward, slide the cable fully in and slide the locking tabs back.
6. On reassembly, do not force the serial connector; it drops in when correctly aligned.

Psion's manual lists the same failure as "membrane keys not responding", with the membrane, daughter board and main board as the causes. For keys on the main keyboard, check for a split keymat first.

SSD and expansion faults

Symptom	Probable cause	Action
SSDs not read in either slot	Door switch out of place, daughter board, main board	Check that the file list updates when the door closes
SSDs not read on a 3mx after the machine has been opened	Snapped microswitch tips, from lifting the main board with the SSD doors closed	Glue the tips back or make new ones; both switches must work before either slot reads. See Psion Series 3mx Troubleshooting Guide
Flash SSD reads but cannot be written or formatted	Daughter board or main board	The +16 V Vh rail supplies the Flash programming voltage and is needed only for writing and formatting
RAM SSD has lost its contents	Flat cell in the pack	Replace the pack's cell
Flash SSD reports full when little is stored	Normal: space from deleted or changed files is recovered only by reformatting	Copy the files off and reformat
3-Link not recognised	Expansion door switch, main board	Check the switch contact

The SSD doors and the expansion door each operate a switch that raises an NMI when a pack or device is inserted or removed. The Psion Series 3c uses tracks and a small metal contact on the door hinge for this; the Psion Series 3mx uses microswitches.

Component-level tests

Supply rails

SIBO supply rails on ASIC9 machines

Rail	Supplies	Notes
Vcc1	ASIC9 and all the memory	Present in every state; nominally 3.3 V; fed from the backup cell in the backup state
Vcc2	The processor, devices shut down in standby, and the expansion port	5 V; off in standby
Vcc3	The LCD module and its drivers	Software switched; 3.3 V on ASIC9 machines
Vcc5	The 5 V pin of the SSD slots	Software switched
Vee1	LCD bias (contrast)	Negative; flyback converter controlled by a DAC
Vh	Flash SSD programming voltage	+16 V; flyback converter; switched on for writing and formatting

Soak test

The Series 3a ROM contains a soak test that needs no test equipment. Reset the machine, then press On while holding the Psion key and the left Shift key. The machine shows "Soak Test" and the elapsed time, and cycles on for about five minutes and off for five minutes until Esc is pressed. Psion used it to keep machines running during environmental and physical testing.

Repair or replace

Psion recommended repairs at board level (main board, daughter board, LCD module, membrane, keymat, battery cable) rather than at component level, because of the high-density surface-mount construction. ASIC9 contains all the core electronics, and Psion's cure for a main board fault is a replacement board. The mechanical repairs are covered in:

• Psion Series 3a Hinge Repair – hinges, and separating the lid for LCD work
• Psion Series 3a General Maintenance – batteries, SSD slots, opening the case
• Psion Series 3a – memory upgrades from 256 KB to 512 KB

Related pages

• Psion Series 3a
• Psion Series 3a General Maintenance
• Psion Series 3a Hinge Repair
• Psion Series 3 Troubleshooting Guide
• Psion Series 3c Troubleshooting Guide
• Psion Series 3mx Troubleshooting Guide
• Psion Siena Troubleshooting Guide
• Battery Explosion, Capacitor or Corrosion Damage
• Recommended Tools