Editing Macintosh IIsi Troubleshooting (section)

== Component-level faults (deep dive) ==

=== Surface-mount capacitor leakage ===

The Macintosh IIsi logic board uses surface-mount electrolytic capacitors whose electrolyte turns corrosive with age and creeps across the board, eating through traces, pads and IC pins. Typical signatures are a machine that will not chime, chimes but shows no video, plays distorted or missing audio, or shows a garbled or checkerboard screen. Wash the affected area and replace every electrolytic with a tantalum or polymer part, then repair any lifted traces. The switch-mode power supply (ASTEC or TDK on the LC-family machines) holds its own electrolytics and fails the same way, so recap it alongside the board.<ref name="caps">Mac84, [https://mac84.net/web/macintosh-lc-series-lc-lc-ii-lc-iii-power-supply-recapping-guide-astec-usa/ Macintosh LC series power-supply recapping guide]; the [http://www.maccaps.com/MacCaps/Capacitor_Reference/Capacitor_Reference.html MacCaps capacitor reference]; and iFixit. Source for surface-mount electrolytic leakage eating traces, pads and pins, the ASTEC/TDK LC power-supply cap failures, and Apple's use of tantalum (non-leaking) capacitors on the Quadra 700/900 logic boards.</ref>

=== PRAM battery ===

The Macintosh IIsi backs up its clock and Parameter RAM from a 3.6&nbsp;V &frac12;AA lithium cell. These cells &mdash; red Maxell parts especially &mdash; leak or burst and corrode the board, so remove an aged one on sight. A flat cell can also stop a soft-power machine booting or disturb the video; left plugged in, trickle power preserves the settings, but a machine switched off at the wall with a dead cell loses them. Clean the area and fit a fresh 3.6&nbsp;V cell.<ref name="pram">[https://68kmla.org/bb/threads/warning-exploding-maxell-pram-batteries.25169/ Warning! Exploding Maxell PRAM batteries], 68kMLA; and [https://www.macdat.net/repair/kb/batteries_macintosh.html Mac Battery Leaks], MacDat. Source for the 3.6&nbsp;V &frac12;AA lithium PRAM cell, the Maxell leak/explosion board damage, and soft- versus hard-power PRAM retention.</ref>

=== Sound loss and video ===

The IIsi blanks its sound when the sprung metal fingers linking the speaker to the logic board oxidise, often only after the machine has warmed up for a while &mdash; clean those contacts. The audio-filter capacitors in the north-west corner of the board are a second cause of lost or distorted sound. For a no-video IIsi, check the PRAM battery before chasing the video path.<ref name="iisi">[https://stason.org/TULARC/os-macintosh/hardware/32-How-can-I-fix-the-sound-on-my-IISI-Macintosh-hardware.html How can I fix the sound on my IIsi?], TULARC; and the [https://www.ifixit.com/Device/Macintosh_IIsi Macintosh IIsi] device page, iFixit. Source for the oxidised speaker-contact sound blanking, the north-west-corner audio filter caps, and the check-the-PRAM-battery-first video guidance.</ref>

=== Boot chime and Sad Mac ===

Read the start-up sound first: a normal chime with a black screen points to the display path or the monitor, an absent chime or a "chord of death" points to RAM or a core fault, and a Sad Mac shows a numeric code &mdash; see [[Sad Mac Error Codes]].