Editing Psion Series 3mx Troubleshooting Guide

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[[File:Psion Series 3mx.jpg|thumb|420px|A Series 3mx. If it will not read an SSD in either slot, suspect the door microswitches before the motherboard — that mistake has cost people a lot of wasted board-swapping.]]

Fault-finding for the '''[[Psion Series 3mx]]''' (1998).

'''The full symptom table, the SIBO power states and the supply rail chart are in the [[Psion Series 3a Troubleshooting Guide]]''', which applies here too. This page covers the 3mx-specific faults — and one of them is important enough to lead with.

== The SSD door microswitch fault ==

'''Symptom:''' the machine reports "'''not ready'''" and '''does not recognise an SSD in either the A or the B slot'''. Everything else works normally.<ref name="rc3mx">Richard Zealley, [https://www.retrocoding.uk/psion-3mx-ssd-microswitch-repair/ "Psion Series 3mx SSD door microswitch repair"], Retro Coding, 25 May 2020. Source for the symptom, the diagnosis, the microswitch arrangement, the damage mechanism, the requirement to repair both switches and the repair method described here.</ref>

'''It looks exactly like a motherboard fault, and it is not.''' One documented case involved buying a second 3mx to test with, swapping motherboards, and finding the fault followed the ''case'' rather than the board — and that the previously-good board then failed in the same way once installed in the damaged machine.<ref name="rc3mx" />

=== Cause ===

The 3mx senses the state of its two SSD slot doors with '''a pair of microswitches set at an angle''' — a different arrangement from the [[Psion Series 3c|3c]], which uses PCB tracks and a small metal connector on the door hinge.<ref name="rc3mx" />

'''The plastic tips of the microswitch buttons snap off''', almost certainly from '''prising up the motherboard with the SSD doors closed'''.<ref name="rc3mx" />

Since the SIBO architecture generates an NMI from the SSD door microswitches and uses them to decide whether a pack is present, a broken switch means the machine never believes a pack is there.<ref name="sibo">Psion PLC, ''SIBO Hardware Reference'', version 2.10, 3 February 1995, in the [https://doc.psion.info/books/the-psion-sibo-software-development-kit/page/hardware-reference Psion Documentation Project]. Source for the NMI generation from SSD and expansion port door microswitches.</ref>

=== Repair ===

# '''Recover the broken plastic tips''' — they are usually still inside the case.
# '''Re-glue each tip onto its switch button with superglue.''' This is straightforward but very fiddly: any glue on your fingers or tools makes it impossible to hold the pieces together while it sets. Once set, the joint is reported as strong.<ref name="rc3mx" />
# '''For a tip that is missing entirely, make a new one''' from a scrap of ABS. This is documented as repairing as well as the re-glued ones.<ref name="rc3mx" />
# '''Watch the tiny spring''' that each switch presses against — it pops out easily and is very easy to lose.<ref name="rc3mx" />
# '''Repair both switches.''' This matters: in the documented case, fixing one was not enough — '''SSDs were only recognised once both switches were repaired and refitted'''.<ref name="rc3mx" />

=== Prevention ===

'''Open both SSD doors before lifting the mainboard.''' Every time.

== Other 3mx-specific symptoms ==

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Symptom !! Cause !! Action
|-
| '''Will not hold data through a battery change''' || '''Wrong backup cell.''' The 3mx takes a '''CR2025'''; the Series 3, 3a and 3c take a '''CR1620''' || Fit a CR2025. A CR1620 is both narrower and thinner and will not make reliable contact.<ref name="wp3">[https://en.wikipedia.org/wiki/Psion_Series_3 "Psion Series 3"], Wikipedia. Source for the CR2025 backup cell on the 3mx, the universal backlight, the fast serial port and the documented clamshell problems.</ref>
|-
| '''Eats batteries''' || '''The backlight''', or the battery lead || Every 3mx is backlit and it is the biggest discretionary load. Check that first, then go to the battery lead.<ref name="wp3" /><ref name="faq">Psion Series 3/3a community FAQ material and the comp.sys.psion newsgroup archives. Source for the battery lead problem and its fix, and the button-bar ribbon reseating trick.</ref>
|-
| '''Serial link will not connect at high speed''' || Mismatched expectations || The 3mx serial port runs up to '''115 kbit/s''', double the 3c. Confirm both ends agree on the rate.<ref name="wp3" />
|-
| '''3a serial cable will not fit''' || '''Expected.''' The 3mx uses the 3c/[[Psion Siena|Siena]] connector || Use the right cable. Travel Modem connections also differ between 3/3a and 3c/3mx.<ref name="wp3" />
|-
| '''No sticky case''' || '''Normal.''' The 3mx is matte silver painted, not rubberised || The sticky-coating problem belongs to the 3c.<ref name="wp3" />
|-
| '''Vertical lines on the display''' || Screen ribbon deterioration || Replace the cable or fit a donor lid. See [[Psion Series 3mx Hinge Repair]].<ref name="wp3" />
|-
| '''Button bar dead''' || Ribbon adrift from the lower PCB || Push it home with a paperclip, lid half closed.<ref name="faq" />
|-
| '''Back edge crooked when opening''' || Broken hidden hinge || See [[Psion Series 3mx Hinge Repair]].
|}

== Everything else ==

For the four SIBO power states, the supply rail chart including the '''+16 V Vh''' rail that Flash SSD writing depends on, the battery lead fault, the keyboard matrix, the full symptom table and the assessment of what is realistically repairable, see '''[[Psion Series 3a Troubleshooting Guide]]'''.

Note that the 3mx runs the '''V30MX at 27.684 MHz''' rather than the V30H at 7.68 MHz, but the SIBO architecture, rails and power states are the same.<ref name="wp3" />

== Related pages ==

* [[Psion Series 3mx]] · [[Psion Series 3mx General Maintenance]] · [[Psion Series 3mx Hinge Repair]]
* [[Psion Series 3a Troubleshooting Guide]] — the shared diagnostic material
* [[Psion Series 3c Troubleshooting Guide]] — the machine with the other door-sensing arrangement
* [[Battery Explosion, Capacitor or Corrosion Damage]] · [[Recommended Tools]]

== References ==

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