Apple II General Maintenance

Apple II with Case Open

The Apple II General Maintenance guide covers procedures for preserving and maintaining Apple II, Apple II Plus, and Apple IIe computers. Regular maintenance prevents common failures that develop after decades of use, particularly socket oxidation, dust and heat damage, and degradation of the switch-mode power supply. This guide addresses cleaning procedures, component inspection, chip reseating and preventive measures specific to the Apple II family.

Where this page gives a number, it comes from the Apple II Reference Manual or from Apple's own Astec power supply service package, both hosted on this wiki. Where Apple never published a figure, this page says so rather than offering one.

Safety Precautions

Working on Apple II computers requires attention to electrical safety and to protecting components from static discharge.

Electrical Safety

Before performing any maintenance:

• Disconnect the mains lead from the computer — not just the rocker switch on the supply, which only breaks the AC input
• Remove all peripheral cards from expansion slots before working on the motherboard
• Disconnect the keyboard cable at the motherboard connector to prevent accidental shorts

The real hazard in an Apple II is the primary side of the power supply. Apple's own wording in the Apple II Reference Manual is that "there are dangerous high voltages inside the power supply's case" and that "much of the internal circuitry is not isolated from the power line". That second half is the part that matters and the part most people miss: the primary side of this supply floats at mains potential. Clipping an ordinary earthed oscilloscope ground to it will put a short across the mains through your probe lead. If you intend to take measurements on the primary side, use an isolation transformer and a differential probe, or do not probe it live at all.

The primary reservoir capacitors are C5 and C6 on the AA11040/B (C2–C5 on the earlier AA11040), rated 47 µF 250 V each. They are not the 2200 µF part that hobbyist lists sometimes describe — that value belongs to the low-voltage secondary side. Discharge them through a resistor of a few kΩ rated for the energy, never by shorting them with a screwdriver, and confirm with a meter that they have actually come down before you work on the board.

The supply also has a class-X capacitor across the mains input: C1, 0.1 µF, specified as a 250 VAC metallised part on the AA11040/B and a 0.1 µF 400 V polyester part on the AA11040. These are the parts that crack, smoke and fill the room with a fish-market smell. See the note under Capacitor Replacement below.

Static Protection

The NMOS and TTL parts in an Apple II are damaged by electrostatic discharge, and the discharge that does it is usually one you never felt. Human perception of a spark from a fingertip starts at roughly 3 kV; device damage starts far below that. Under the current classification standard, ANSI/ESDA/JEDEC JS-001, a component is Class 1A if it fails between 250 V and 500 V, Class 2 between 2 kV and 4 kV, and Class 3A between 4 kV and 8 kV. So a discharge well under the threshold at which you notice anything can sit inside the sensitivity range of the most fragile parts on the board.

Essential precautions:

• Use an anti-static mat when working on circuit boards, connected to a proper ground point
• Wear an anti-static wrist strap — the resistor in the strap cord is there for your safety, so never substitute a plain wire
• Store chips in anti-static foam or conductive bags when removed from sockets
• Handle chips by their edges only, never touching the pins directly
• Avoid very dry conditions — dry air is what lets a charge build up on you in the first place. Do not go the other way and work in a damp room either; condensation and corrosion are their own problem, and the storage figures further down this page are the ones to aim for
• Avoid wearing polyester clothing or working near plastic materials

When anti-static equipment is unavailable, touch a grounded metal surface before handling chips, and keep touching the chassis while you work. Anti-static bags from electronic components can serve as a temporary work surface, but never power the computer while it is sitting on conductive material.

Chip Reseating

Poor socket connections are one of the most common problems with Apple II computers, because the Apple II and II Plus have nearly everything socketed and the sockets have had forty years to oxidise.

Identifying Problem Connections

Symptoms of oxidised connections include:

• System fails to boot or displays garbage characters
• Random crashes during operation
• Keyboard keys not responding or producing wrong characters
• Memory errors appearing intermittently
• Video display problems including colour fringing or missing text

The oxide forms an insulating layer between chip pins and socket contacts, creating high-resistance connections that prevent proper signal transmission.

Proper Reseating Technique

For systematic reseating:

1. Document chip positions before removal — photograph the motherboard or create a diagram showing chip orientations
2. Use a proper IC extractor — insert the tool ends under opposite corners of the chip
3. Rock gently while lifting — never pull straight up, which can bend pins
4. Inspect each chip for bent or corroded pins before reinsertion
5. Clean pins if oxidised using a pencil eraser or fibreglass pen
6. Align carefully — ensure all pins enter the socket before pressing down
7. Press firmly and evenly using thumb pressure on the centre of the chip

Work methodically through one row at a time. On the Apple II and II Plus the board is laid out as a grid, with row letters down one edge and column numbers along the other, so chips are identified as F12, E11, C1 and so on. The three rows of RAM are C, D and E, with row C frontmost, and the six ROM sockets sit above them.

Special Considerations for Different Models

Apple II and Apple II Plus:

• The three memory configuration blocks at D1, E1 and F1 are 14-pin jumper blocks, not ICs. They strap each RAM row into a place in the memory map, and all three must be strapped identically. Pull them, clean them and put them back the same way round — a swapped or missing block produces a machine that boots to garbage or reports the wrong memory size
• The 74LS138 at F12 selects the individual ROMs; if all ROMs appear dead, suspect it before you suspect six ROMs
• 4116 RAM (16K × 1) needs three supplies — +12 V, +5 V and −5 V. This is why the Apple II supply has a −5 V rail at all. A missing or sagging −5 V or +12 V rail presents as memory failure, not as a power fault, so check the rails before you start pulling RAM
• Do not substitute 2716 EPROMs for the mask ROMs. Apple states that the ROMs are similar to the 2316 and 2716, "however, the chip selects on most of these PROMs are of a different polarity, and they cannot be plugged directly into the Apple board". The manual gives the 9316B pinout as the reference

Apple IIe:

• The IIe grid runs A–F down the side and 1–14 along the bottom. The 6502B is at B4; the MMU at D4, the IOU at D6 and the HAL at D1; the video ROM at F4, the CD (Applesoft) ROM at D10, the EF (monitor) ROM at D8, the keyboard ROM at D12 and the AY-3600 keyboard decoder at D14. The eight 64K × 1 DRAMs occupy F6–F13
• The custom parts — MMU, IOU and HAL — are the ones to be careful with, both because they are static-sensitive and because they are the hardest to replace

Internal Cleaning

Dust accumulation inside Apple II computers traps heat and holds moisture against the board.

Motherboard Cleaning

For routine dust removal:

1. Use compressed air held at an angle to avoid forcing dust deeper into sockets
2. Work from top to bottom allowing dust to fall away from cleaned areas
3. Focus on heat-generating areas around the power supply connector
4. Clean between expansion slots where dust accumulates heavily

For thorough cleaning of heavily contaminated boards:

1. Remove all socketed ICs and store safely in anti-static foam
2. Wash with warm water and a little detergent using a soft brush for stubborn areas
3. Rinse thoroughly with distilled water to remove all detergent residue
4. Shake vigorously to remove water from sockets and from under components
5. Dry completely — at least 48 hours in a warm, dry place before reassembly, longer if the board has sockets
6. Flood with isopropyl alcohol (99%) afterwards to displace trapped water

Water washing removes decades of contamination but only works if the board is genuinely dry before power is applied. Trapped water under a socket will corrode quietly for months. Do not wash the keyboard assembly or anything with a sealed switch or a paper label this way.

Keyboard Maintenance

Apple II keyboards accumulate debris that causes sticky or non-responsive keys.

Keycap cleaning:

1. Remove keycaps carefully using a keycap puller
2. Soak in warm soapy water
3. Scrub with a soft brush to remove ingrained dirt
4. Rinse and dry completely before replacement

Keyswitch cleaning:

1. Apply 99% isopropyl alcohol to the switch mechanism using a squeeze bottle
2. Work the switch repeatedly to distribute the cleaner and break through oxide
3. Allow complete evaporation before testing
4. Repeat if necessary for stubborn switches

The Apple II and II Plus keyboard is built around an MM5740 keyboard decoder ROM, whose outputs are buffered by a 7404 and taken to the keyboard connector on the main board. The scanning oscillator is three sections of a 7400 at keyboard location U4, and the 10 Hz auto-repeat comes from a 555 at U3; the repeat rate is set by R3, a 220 kΩ resistor. The Apple IIe uses an AY-3600 decoder at D14 instead. Both decoders are static-sensitive and neither is easy to source, so ground yourself before touching either.

Case Maintenance

The injection-moulded plastic cases yellow and become brittle with age, and need careful cleaning to avoid damage.

Basic Cleaning

For routine case cleaning:

• Warm water with a little washing-up liquid on a soft cloth removes most surface grime
• Use cotton swabs for cleaning around the raised Apple logo and ventilation slots
• Rinse with clean water and dry thoroughly
• Do not use household bleach. Sodium hypochlorite attacks ABS, is no use against the bromine-driven yellowing these cases suffer from, and produces chlorine gas if it meets an acidic or ammonia-based cleaner. If you want to reverse yellowing, use the peroxide method below
• Avoid silicone-based furniture polishes. They leave a residue that is difficult to remove and that interferes with later retrobrighting or painting

Removing Stubborn Stains

For persistent marks:

• Isopropyl alcohol removes adhesive residue and ink marks
• Melamine foam ("Magic Eraser") gently abrades surface contamination — it is an abrasive, so it will dull a textured finish if you lean on it
• Anything gritty will leave scratches. Test in a hidden area first and accept a dull patch as the likely outcome

Painted cases require extra care — test cleaning products on hidden areas first. The paint on Bell & Howell black Apple II Plus models is particularly fragile.

Retrobrighting

Main article: Retrobrite

Severely yellowed cases can be treated with hydrogen peroxide. The process, its risks, and the fact that results are not permanent are covered on the Retrobrite page; read it before committing a case to it.

Expansion Slot Maintenance

The Apple II, II Plus and IIe have eight peripheral slots, numbered 0 to 7. (The IIe reassigns slot 0 to the auxiliary connector.) Oxidation in the slots prevents cards from working properly and is a far more common cause of a dead card than a genuinely faulty card.

Cleaning Procedures

For each slot:

1. Spray contact cleaner into the slot opening
2. Insert and remove a sacrificial card several times to scrub the contacts
3. Allow the cleaner to evaporate completely before installing cards
4. Apply a contact enhancer if you use one, sparingly

Card Edge Connector Treatment

Expansion cards require similar maintenance:

• Clean edge connectors with isopropyl alcohol and a lint-free cloth
• Polish with a pencil eraser for stubborn oxidation, then clean off the eraser crumbs
• Never use sandpaper or a fibreglass pen on gold fingers — the plating is microns thick and does not come back
• Check for worn contacts appearing as dark or coppery patches where the gold has gone

Note also that the INH (ROM inhibit) line runs to every slot, and a card that pulls it low disables every ROM on the main board. A machine that boots with all cards out and produces nothing with one card in is worth checking against that before condemning the motherboard.

Power Supply Maintenance

The Apple II power supply is an Apple design — U.S. Patent 4,130,862 — built for Apple by Astec, and it is the machine's characteristic failure. You are allowed to work on it; just understand what is in there first (see Electrical Safety above).

Published specification

Apple's figures, from page 92 of the Apple II Reference Manual:

Parameter	Apple's published figure
Input voltage	107–132 VAC, or 214–264 VAC (switch selectable on supplies that have the selector)
Supply voltages	+5.0 V, +11.8 V, −12.0 V, −5.2 V
Full-load output	+5 V at 2.5 A; −5 V at 250 mA; +12 V at 1.5 A (about 2.5 A intermittent); −12 V at 250 mA
Power consumption	60 W maximum at full load; 79 W maximum intermittent
Operating temperature	55 °C (131 °F)

Two things are worth pulling out of that table. First, the nominal for the "+12 V" rail is +11.8 V and the nominal for the "−5 V" rail is −5.2 V; a supply reading 11.85 V is on specification, not low. Second, Apple published no per-rail tolerance band — not in the Reference Manual, not in the Astec service package. Figures such as "+5 V should read 4.85 V to 5.15 V" circulate widely and have no manufacturer source behind them.

Voltage Verification

Measure at the motherboard power connector with the system running and a representative set of cards fitted. In the absence of an Apple tolerance figure, the defensible check is the one the load imposes: the board is full of 74LS-series TTL, which is specified for a 5 V supply at ±5 per cent, so 4.75 V to 5.25 V on the +5 V rail is the range in which every part on the board is being run inside its own datasheet. Aim for 5.00 V and treat drift upward as worse than drift downward, because it costs chip life for nothing.

For the other three rails, compare against Apple's nominals of +11.8 V, −12.0 V and −5.2 V. A rail that is out by more than a few per cent, or that visibly moves when a drive spins up, is worth investigating. A rail that is dead is usually a failed secondary rectifier or a dried-out output capacitor rather than a failed supply.

Also check ripple with an oscilloscope on AC coupling if you have one. A supply that measures correctly on a DC meter and still crashes the machine is normally a supply with a dried output capacitor and tens of millivolts of switching noise riding on the rails.

Load Testing

The supply can be tested off the machine, but it needs a load. Apple's rated currents give the resistor values:

Rail	Nominal	Rated current	Resistor for about half rated load	Dissipation
+5 V	+5.0 V	2.5 A	4 Ω	about 6 W
+12 V	+11.8 V	1.5 A	15 Ω	about 9 W
−5 V	−5.2 V	250 mA	47 Ω	about 0.6 W
−12 V	−12.0 V	250 mA	100 Ω	about 1.4 W

Rate the resistors generously. A 15 Ω resistor across 11.8 V dissipates close to 9 W; a "10 W" wirewound running at 9 W gets hot enough to scorch the bench and drift in value. Use at least double the calculated dissipation, mount the resistors clear of anything flammable, and do not leave the test running unattended.

Understand what the supply does into a fault before you condemn it. Apple describes the behaviour explicitly: if one of the outputs is short-circuited, a feedback circuit stops the oscillator and cuts all outputs, the supply pauses for about a second, and then it tries to start again. The result is the familiar tick-tick-tick. A ticking Apple II supply is a supply doing its job — it is telling you something downstream is loaded or shorted. Pull every card, disconnect the drives, and try again before assuming the supply is the fault.

Visual Inspection

When the case is open, check:

• The class-X mains capacitor (C1, 0.1 µF) — any crazing, cracking, swelling or brown staining of the epoxy means it goes now
• Bulging or leaking electrolytics on the secondary side
• Burn marks or discoloured board around the switching transistor and the secondary rectifiers
• Corroded connections at the output connector
• The inrush thermistor (R1) and the mains varistor (VDR1, 260 VAC) for cracks

Capacitor Replacement

Apple's own Astec component listings give the values, so there is no need to guess. For the AA11040/B:

• C1 — 0.1 µF, 250 VAC metallised (class-X, across the mains)
• C3, C4 — 2200 pF, 400 VAC ceramic (class-Y)
• C5, C6 — 47 µF 250 V electrolytic (primary reservoir)
• C7 — 220 µF 10 V
• C12, C13, C14, C19 — 1000 µF 10 V
• C15, C16 — 220 µF 10 V
• C20 — 680 µF 16 V
• C21, C22 — 330 µF 16 V
• C24, C25 — 47 µF 250 V
• F1 — 2.75 A 125 V fuse; VDR1 — 260 VAC varistor; R1 — 4 Ω or 5 Ω inrush thermistor

The earlier AA11040 differs: C1 is a 0.1 µF 400 V polyester part, C2–C5 are the four 47 µF 250 V primary electrolytics, C6 is a 22 µF 16 V tantalum, C9/C10/C13/C15 are 1000 µF 10 V, C11/C18 are 330 µF 16 V, C12/C16 are 220 µF 10 V, C17 is 680 µF 16 V, and F1 is a 2.75 A 250 V fuse. Check which board you have before ordering.

Priorities:

• The class-X capacitor first. A cracked 1970s or 1980s X capacitor is the single most likely thing to fail dramatically in an Apple II. Replace it with a modern X2-rated part of the same value. Replaced once with a current part, it does not need replacing again on any schedule — the advice to swap safety capacitors every year or two has no basis
• The primary reservoir capacitors next, since a dried 47 µF 250 V part makes the supply unstable under load
• Then the secondary electrolytics, where 105 °C low-ESR replacements are a genuine improvement over the originals

ROM and RAM Identification

ROM sockets

The Apple II board has six ROM sockets above the RAM rows, and they are silkscreened with the address range each one covers rather than with a socket number: D0, D8, E0, E8, F0 and F8. What is fitted depends on the machine:

Apple II (Integer BASIC):

• Integer BASIC and its support code occupy the E0, E8 and F0 sockets; the Mini-Assembler, the Floating-Point Package and the SWEET-16 interpreter live in the Integer BASIC ROMs
• F8 holds the monitor (original Monitor or, later, Autostart)
• D0 and D8 are often empty on an Integer machine. The Programmer's Aid #1 ROM goes at D0. An empty socket here is not a fault

Apple II Plus (Applesoft):

• Applesoft II BASIC occupies D0, D8, E0, E8 and F0
• F8 holds the Autostart Monitor
• The Mini-Assembler, Floating-Point Package and SWEET-16 are not present on a II Plus, because they lived in the Integer ROMs that Applesoft replaced

Apple IIe:

• Two ROMs only — CD at D10 and EF at D8 — plus a separate video ROM at F4

RAM Configuration

The Apple II and II Plus take three rows of eight RAM chips, rows C, D and E, front to back. Each row must hold eight of the same type, though different rows may hold different types.

• 4K parts are the Mostek 4096 family, marked MK4096 or MCM6604
• 16K parts are the 4116 type, marked MK4116 or µPD4160
• Date codes are in YYWW form (year and week of manufacture)

Apple supported nine memory configurations built from combinations of those two types: 4K, 8K, 12K, 16K, 20K, 24K, 32K, 36K and 48K. The three memory configuration blocks at D1, E1 and F1 tell the machine which row is which; all three must be strapped the same way. A Language Card takes a 48K machine to 64K.

The Apple IIe is 64K as standard from eight 64K × 1 DRAMs at F6–F13, and goes to 128K with an auxiliary-slot card.

On-board voltage regulation

There is none, and this is worth stating because guides sometimes describe servicing it. The Apple II, II Plus and IIe main boards take all four rails directly from the power supply — the supply itself regulates them, by comparing the +5 V output against a reference and adjusting the oscillator. There are no 78xx or 79xx linear regulators on these boards and no regulator heat sink to inspect, re-paste or replace. If a rail is wrong at the board, the fault is in the supply, in the connector, or in something on the board pulling the rail down.

Preventive Maintenance Schedule

Most Apple II failures are caused by storage, not by use. The schedule below reflects that.

Occasionally, if the machine is in use

• Check the rails at the motherboard connector if you have a meter
• Exercise all the keys
• Look and listen for anything new — a tick from the supply, a smell, a display that takes longer to settle

Annually

• Open the case and clean the interior
• Reseat the socketed chips that matter: CPU, ROMs, the memory configuration blocks, and the F12 ROM decoder
• Inspect the power supply's class-X capacitor and the secondary electrolytics
• Clean expansion slots and card edges
• Measure and write down the rail voltages, so that next year's reading has something to be compared against

Before and after long storage

• Take out any batteries in peripherals before storing
• On return to service, inspect before powering: rodent damage, corrosion around battery holders, anything that has grown in the case
• Power up for the first time with all cards removed

Note on "exercising" equipment: running a machine occasionally does no harm, and it does give a dried capacitor a chance to announce itself while you are watching. But the idea that a fixed monthly run prevents capacitor deterioration is folklore, not a manufacturer recommendation, and no such schedule appears in any Apple documentation for this machine.

Storage Guidelines

Environmental Conditions

Aim for:

• Temperature: 15–24 °C (60–75 °F)
• Humidity: 30–50% relative humidity
• Light exposure: avoid direct sunlight and fluorescent lighting — UV is what drives the case yellowing
• Dust protection: dust covers or sealed containers

Silica gel in sealed containers helps control humidity. High humidity accelerates corrosion; very low humidity makes static a bigger problem when you come to handle the machine again.

Preparation for Storage

1. Clean thoroughly inside and out
2. Remove batteries from any peripherals — see Battery Explosion, Capacitor or Corrosion Damage for what happens if you do not
3. Wrap in anti-static material rather than ordinary plastic bags
4. Document condition including any known issues
5. Store on its base or on edge, supported, so the board is not flexing under the weight of cards
6. Include desiccant packets

Reactivation After Storage

1. Inspect for rodent damage to cables and boards
2. Check for corrosion particularly around battery holders on cards
3. Clean and reseat chips before first power-up
4. Test the supply on a dummy load before connecting it to the motherboard
5. Power up with no cards fitted, then add cards one at a time
6. Run diagnostics to verify proper operation

Troubleshooting Common Problems

No power, or a ticking supply

1. A tick-and-retry cycle means the supply has detected a fault and is protecting itself. Remove all cards, disconnect the drives, and retry
2. If it still ticks with nothing connected, the fault is in the supply or on the motherboard
3. If it now starts, add cards back one at a time to find the loaded one
4. Measure all four rails at the motherboard connector against Apple's nominals

No boot, garbage screen

1. Reseat the ROMs and check the 74LS138 at F12 that selects them
2. Reseat the RAM, and check the three configuration blocks at D1, E1 and F1 are present, correct and identically strapped
3. Check the −5 V and +12 V rails before blaming the 4116s — a missing bias rail looks exactly like bad RAM
4. Check whether any card is pulling the INH line low
5. Reseat the character generator ROM if text is garbled but graphics behave

Video problems

1. All timing on the board derives from the 14.31818 MHz master oscillator, which also produces 7.159 MHz, the 3.58 MHz colour reference and the two 1.023 MHz system clock phases
2. If the machine runs but video is unstable, check that oscillator first
3. Note that the 14 MHz and colour-reference signals are not present on the peripheral connectors, so a video card cannot be the source of a fault in them

Keyboard problems

1. Clean affected keyswitches with alcohol
2. Check the keyboard connector at the motherboard
3. Reseat the encoder — MM5740 on the II and II Plus, AY-3600 at D14 on the IIe
4. Check cable continuity

Disk drive issues

1. Clean drive heads with isopropyl alcohol
2. Check cable connections and orientation
3. Clean the controller card's edge connector
4. See Floppy Drive Repair for drive-side work

Test Equipment Recommendations

Basic maintenance requires:

• Digital multimeter for voltage measurements
• Anti-static mat and wrist strap
• IC extraction tool
• Contact cleaner
• 99% isopropyl alcohol
• Compressed air
• Soft brushes and cotton swabs
• Power resistors for load-testing the supply, rated well above the calculated dissipation

Advanced troubleshooting benefits from:

• Oscilloscope — the fastest signal you need to see is the 14.31818 MHz master clock, so a 50–100 MHz instrument is comfortable and anything faster is a luxury
• Logic probe for digital signal testing
• EPROM programmer for ROM replacement — remember the chip-select polarity problem noted above
• ESR meter for capacitor testing

See Recommended Tools for the wiki's general bench kit.

Related pages

• Apple II Reference Manual — Apple's own manual, hosted here
• Apple Astec Power Supplies Service Package — Apple's power supply schematics and component listings
• Battery Explosion, Capacitor or Corrosion Damage
• Capacitor Failure Symptoms
• Retrobrite