Editing Macintosh LC General Maintenance

This page covers routine care for the original '''[[Macintosh LC]]''' (logic board 630-0309, 1990). The chassis, power supply, battery and take-apart procedure are shared with the [[Macintosh LC II]], [[Macintosh LC III]], [[Macintosh LC III+]], [[Macintosh LC 475]] and [[Macintosh Quadra 605]]; the logic boards are not.

Every figure below comes either from Apple's own ''Service Source'' for the LC series and Quadra&nbsp;605 or from Apple's ''Macintosh LC Developer Note'', both hosted on this wiki. Where a figure is in neither, it is not given.<ref name="ss-lcser">Apple Computer, ''Service Source: Macintosh LC Series / Quadra 605''. Hosted on this wiki as [[:File:Quadra 605.lc series.pdf]]; see [[Macintosh LC Series/ Quadra 605 Service Source]]. Chapters used: Specifications (Processor, Memory, I/O Interfaces, Sound and Video, Electrical, Physical), Troubleshooting (Symptom Charts), Take Apart, Additional Procedures (Battery Verification) and Exploded View.</ref><ref name="dn-lc">Apple Computer, ''Macintosh LC Developer Note'' (1990). Hosted on this wiki as [[:File:Macintosh LC Developer Note.pdf]]; see [[Macintosh LC Developer Note]]. Expansion connector signal list and power budget.</ref>

== What this machine is ==

{| class="wikitable styled-table" style="width:85%;"
|+ Apple's specification for the Macintosh LC
! Item !! Figure
|-
| Processor || Motorola 68020 at 16 MHz, on a 16-bit data bus
|-
| DRAM || 2 MB standard, expandable to '''10 MB''' (100 ns or faster SIMMs)
|-
| ROM || 512 K
|-
| VRAM || 256 K, upgradable to 512 K
|-
| Expansion || 96-pin processor-direct slot for an 020 direct-slot card
|-
| Sound || Monaural 8-bit input at 11 or 22 kHz; monophonic 8-bit generator feeding the same signal to both channels
|-
| Dimensions || 3.0 × 12.2 × 15.0 in (7.7 × 31.0 × 38.2 cm)
|-
| Weight || 8.8 lb (4.0 kg)
|}

All of the above is Apple's.<ref name="ss-lcser" /> Two consequences are worth knowing before you start diagnosing:

* '''The 10&nbsp;MB ceiling is real.''' You can fit 12&nbsp;MB and the machine will still only address 10. That is Apple's own figure, not a fault and not something a different SIMM will fix.<ref name="ss-lcser" />
* '''There is no stereo output.''' Apple specifies a monophonic generator feeding both channels on the LC, LC&nbsp;II and LC&nbsp;III. Only the LC&nbsp;475 and Quadra&nbsp;605 in this family are genuinely stereo.<ref name="ss-lcser" />

== Power supply ==

Every "pizza box" machine in this family — LC, LC&nbsp;II, LC&nbsp;III, LC&nbsp;III+, LC&nbsp;475 and Quadra&nbsp;605 — takes the same power supply, which Apple lists as a single service part, '''661-1733'''.<ref name="ss-lcser" /> It is a universal auto-ranging switch-mode unit covering '''100–240&nbsp;VAC''', so there is no voltage selector to set wrongly and no separate 120&nbsp;V and 230&nbsp;V board to confuse.<ref name="ss-lcser" />

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:80%;"
|+ Apple's electrical specification
! Item !! Figure
|-
| Line voltage || 100–240 VAC, automatically configured
|-
| Frequency || 47–63 Hz
|-
| Maximum power, LC || '''50 W''', monitor excluded
|}

Note what that figure is: the '''machine's''' maximum consumption, not the supply's rating. The same 661-1733 supply is fitted to a 50&nbsp;W LC and a 26&nbsp;W Quadra&nbsp;605.<ref name="ss-lcser" />

=== What Apple does and does not publish ===

'''Apple publishes no rail tolerance and no power-supply adjustment procedure for this machine.''' The ''Service Source'' carries no acceptable-range table for the +5&nbsp;V, +12&nbsp;V or −5&nbsp;V rails and no trimmer adjustment; every power fault in the symptom charts ends in "Replace power supply".<ref name="ss-lcser" /> The "+5&nbsp;V 4.85–5.15&nbsp;V / +12&nbsp;V 11.9–12.7&nbsp;V" table that circulates on pages of this era is Apple's '''Macintosh Plus''' procedure — genuine there, where it uses voltage test cable 077-0135 on the external floppy port — copied onto machines it was never written for. It has been removed from this page rather than reproduced.

What you can do instead is compare against a known load. With the machine running, each rail at the logic-board power connector should sit close to its nominal value and should not move when a drive spins up. A rail that is visibly low, or that sags under load, points at the supply. A rail that measures as a short to ground with the supply disconnected points at the logic board.

=== Recapping it ===

You are allowed to open this supply — tired electrolytics in it are one of the commonest reasons one of these machines will not start. Understand what is live inside first. It is fed straight from the mains, so with the cover off and the lead in, the fuse, input filter, bridge rectifier and bulk capacitor all sit at mains potential. The bulk capacitor charges to roughly the peak of the incoming waveform — about 170&nbsp;V on 120&nbsp;V mains, about 340&nbsp;V on 230&nbsp;V mains — and holds a useful fraction of that after the plug comes out. Unplug, wait, then measure across the bulk capacitor and confirm it reads a few volts before a tool goes near the primary side.

Apple bought this supply from several vendors and their capacitor complements differ, so read the maker's label before ordering parts. The per-variant lists are on [[Macintosh LC Capacitor Replacement Guide]].

'''Removing it:''' disconnect the power supply cable from the logic board, release the two latches that hold the front end of the supply to the bottom case, and lift it out.<ref name="ss-lcser" />

== PRAM battery ==

Apple's part is a '''3.6&nbsp;V lithium half-AA cell, part number 742-0011''', in a clip-in holder on the logic board. It appears under that number in the exploded view Apple prints for the whole LC series and the Quadra&nbsp;605.<ref name="ss-lcser" />

'''Apple's check is a measurement, not a calendar.''' Set a meter to the 10&nbsp;V DC range, put the positive probe on the positive end of the cell and the negative probe on the negative end, and '''replace the cell if it reads below 3.0&nbsp;V'''.<ref name="ss-lcser" /> Apple publishes no replacement interval for this battery and none is given here: a cell above 3.0&nbsp;V is doing its job, and one below it should come out today whatever its age.

=== If it has leaked ===

'''This is a lithium cell, so neutralise with bicarbonate of soda, not vinegar.''' Vinegar is the right treatment for an alkaline cell, whose leakage is basic. It is the wrong treatment here, and it adds water and chloride to an already corroded board. Use a paste of sodium bicarbonate and distilled water, rinse with distilled water, follow with isopropyl alcohol and dry thoroughly.

Then check the damage instead of assuming there is none:

* Inspect under magnification for traces that have gone dull, green or thin.
* Buzz out every track running away from the holder. Corrosion travels under the solder mask and does not show from above.
* Look at the underside of the board. Electrolyte wicks down through vias and comes out the other side.

See [[Battery Explosion, Capacitor or Corrosion Damage]] and [[Battery Refurbishment]].

'''Take the cell out before the machine goes into storage.''' That is not a service interval; it is the one measure that reliably prevents this damage.

== Cleaning ==

=== Opening the case ===

# Disconnect everything.
# '''Remove the case screw if one is fitted.''' Not every machine has one.<ref name="ss-lcser" />
# Lift the tabs at the back of the lid and lift the top cover straight up.<ref name="ss-lcser" />

=== Inside ===

* Compressed air and an anti-static brush on the logic board, the supply and the fan. Hold the fan blade still while you blow it: spinning a fan with compressed air drives it as a generator and puts a reverse voltage back down its cable.
* Isopropyl alcohol (99&nbsp;%) and a soft brush for grime, working outwards from each capacitor and from the battery holder.
* Look at the underside of the board too. Both battery and capacitor electrolyte travel through vias.

=== Outside ===

* A damp microfibre cloth and mild detergent. No abrasives, no solvents — the texture on these shells does not survive either.
* ADB keyboards come apart for washing: keycaps off, warm soapy water, dry them completely, then clean the contacts with isopropyl alcohol.
* Mouse ball out, rollers scraped and wiped with isopropyl alcohol.

The platinum-grey plastics yellow with age. The discolouration is in the body of the plastic rather than on the surface, so cleaning will not shift it; see [[Retrobrite]] for what can be done about it and what it costs in brittleness.

=== Fan and speaker ===

On the original LC the fan and speaker are a single '''fan/speaker assembly''', held into the bottom case by a latch at each end: release one latch, lift slightly, release the other, lift the assembly out.<ref name="ss-lcser" /> The LC&nbsp;II and later use a separate fan with its own cable.<ref name="ss-lcser" />

Apple's expansion connector carries a '''FAN''' signal, and a card that grounds it digitally raises the fan speed to improve thermal conditions inside the case.<ref name="dn-lc" /> A machine whose fan runs faster than you expect with a card fitted is doing what the card asked for.

== Connectors and sockets ==

Oxidised contacts are the commonest cause of intermittent faults on a machine this age, and the cheapest to put right.

* '''SIMM sockets.''' Clean with isopropyl alcohol on a swab and reseat. Do not take an abrasive to a SIMM's gold fingers — once you are through the plating, the base metal oxidises and then transfers to every socket the module touches.
* '''VRAM sockets.''' Same treatment. Video faults that come and go when the case is knocked usually start here.
* '''Expansion slot.''' Check for bent contacts and debris before a card goes home.
* '''Logic-board power connector.''' Look for browning or a distorted housing. A discoloured power connector is a warning, not a cosmetic problem.
* '''SCSI and floppy headers.''' Reseat, and check the ribbon for cracked conductors where it folds.

A contact cleaner such as DeoxIT D5 earns its place on genuinely corroded contacts. It is not a preventive treatment and it does not belong on clean gold.

== Expansion slot ==

The LC's 96-pin connector supplies '''+5&nbsp;V at 800&nbsp;mA, −5&nbsp;V at 20&nbsp;mA and +12&nbsp;V at 200&nbsp;mA''', and Apple limits a card to '''4&nbsp;watts total''' however it is drawn across the three rails. Apple's warning is explicit: a card dissipating more than 4&nbsp;watts may overheat and damage the computer's circuitry or make it inoperable.<ref name="dn-lc" />

Those numbers are also a diagnostic. The −5&nbsp;V rail is budgeted at 20&nbsp;mA at the slot precisely because it is a weak rail on this design — it exists mainly to feed the RS-422 serial drivers — so a failed or reversed capacitor on it pulls it down rather than destroying anything, and shows up as modem and printer-port trouble and nothing else.

== Capacitors ==

Fifteen surface-mount electrolytics on logic board '''630-0309''': eight 10&nbsp;µF 16&nbsp;V, five 47&nbsp;µF 16&nbsp;V, one 100&nbsp;µF 6.3&nbsp;V and one 1&nbsp;µF 50&nbsp;V.<ref name="console5" /> The per-designator list, the revision note about C9, the board photograph and the full procedure are on [[Macintosh LC Capacitor Replacement Guide]].

Sound goes first on these boards, then intermittent starting, then visible residue. A leaking surface-mount electrolytic does not have to look swollen — the usual failure is a seeped seal, and the evidence hides under the can. See [[Capacitor Failure Symptoms]].

== Floppy drive ==

'''The 1.4&nbsp;MB Apple SuperDrive is direct drive. It has no belt.''' Advice to fit a new belt to a sluggish or non-ejecting SuperDrive is wrong: there is nothing there to replace. What these drives actually suffer is hardened grease on the head carriage and eject rails, dust in the mechanism, and dirty or worn heads.

* Clean the heads with isopropyl alcohol on a lint-free swab, supporting the upper head arm so it is not sprung.
* If the rails are stiff, re-lubricate with a '''silicone''' grease — not white lithium grease, which gums up as it ages.
* Apple's own replacement notes: remove the dust shield, if present, before fitting a replacement SuperDrive, and replace drives like for like, auto-inject for auto-inject and manual-eject for manual-eject.<ref name="ss-lcser" />

See [[Macintosh Floppy Drive Maintenance]].

== Hard disk ==

The original SCSI mechanisms are thirty years old and the usual failures are a stuck spindle, dried head-park grease and dead controller electronics. Solid-state replacements — BlueSCSI, ZuluSCSI, SCSI2SD — are quieter, cooler and considerably more reliable, and they let you keep the original drive on a shelf as a spare.

Whatever you fit, get the termination right: the internal drive on these machines is the end of the bus and must be terminated, and the computer itself is always SCSI ID 7. See [[Macintosh HDD Maintenance]].

== Storage ==

* '''Take the battery out.'''
* Store dry and at room temperature. Not a loft, not a garage.
* If the logic board comes out, bag it anti-statically and lay it flat.
* Nothing needs periodic running. "Power it up every few months to keep the capacitors formed" is repeated widely and supported nowhere for machines of this kind. The real hazard to a stored Macintosh is the cell in the battery holder, and removing it costs nothing.

== Related pages ==
* [[Macintosh LC]]
* [[Macintosh LC Capacitor Replacement Guide]]
* [[Macintosh LC Troubleshooting]]
* [[Macintosh LC Series/ Quadra 605 Service Source]]
* [[Macintosh LC Developer Note]]
* [[Recommended Tools]]

== References ==
<references />

[[Category:Apple Vintage Computers]]
[[Category:Apple Maintenance Guides]]
{{Navbox-AppleVintage|state=collapsed}}