Apple II General Maintenance

Inside an Apple II Plus: power supply on the left, cards in the slots, RAM rows in front

Routine maintenance of the Apple II, Apple II Plus and Apple IIe deals mostly with oxidised sockets and slots, dust, and ageing capacitors in the switch-mode power supply. The figures below come from Apple's Apple II Reference Manual, the Apple IIe Reference Manual, Apple's Astec power supply service package and Apple's service Technical Procedures, all hosted here.

Safety precautions

Electrical safety

Before starting:

• Unplug the mains lead. The rocker switch on the supply only breaks the AC input.
• Remove all peripheral cards before working on the motherboard.
• Disconnect the keyboard cable at the motherboard connector.
• Apple's take-apart procedure says to touch the power supply case before touching anything inside, to discharge yourself.

The real hazard in an Apple II is the primary side of the power supply. The Apple II Reference Manual warns: "There are dangerous high voltages inside the power supply's case. Much of the internal circuitry is not isolated from the power line, and special equipment is needed for service." The primary side floats at mains potential, so clipping an earthed oscilloscope ground to it shorts the mains through the probe lead. To measure the primary side, use an isolation transformer and a differential probe, or do not probe it live.

The AA11040B supply has four 47 µF 250 V electrolytics, C5, C6, C24 and C25, and the earlier AA11040 has four at C2 to C5. Discharge the reservoirs through a resistor of a few kΩ rated for the energy, never with a screwdriver, and confirm with a meter that they are down before working on the board.

The supply also has a class-X capacitor across the mains input: C1, 0.1 µF, a 250 VAC metallised part on the AA11040B and a 0.1 µF 400 V polyester part on the AA11040. Old X capacitors of this kind crack and can smoke; see Capacitor replacement below.

Static protection

The NMOS and TTL parts in an Apple II can be damaged by an electrostatic discharge too small to feel. A spark from a fingertip becomes noticeable at roughly 3 kV, while under ANSI/ESDA/JEDEC JS-001 a Class 1A part fails between 250 V and 500 V and a Class 2 part between 2 kV and 4 kV.

• Work on a grounded anti-static mat and wear a wrist strap. The strap's series resistor is there for your safety; never replace it with a plain wire.
• Store removed chips in conductive foam or bags, and handle them by the body, not the pins.
• Very dry air lets charge build up. A damp room brings condensation and corrosion instead.
• Without anti-static equipment, touch a grounded metal surface before handling chips. Never power the computer while it sits on conductive material.

Chip reseating

The Apple II and II Plus have nearly everything socketed, and forty-year-old sockets oxidise. Oxidised contacts show as a machine that will not boot or shows garbage, random crashes, keys that give the wrong character, intermittent memory errors, and video faults.

1. Photograph the board before removing anything, so every chip goes back in the same place and the same way round.
2. Lever chips out with an IC extractor or a small screwdriver under alternate ends, rocking gently. Pulling straight up bends pins.
3. Inspect each chip for bent or corroded pins; clean light oxidation with a pencil eraser.
4. Align all the pins with the socket before pressing down, then press firmly and evenly on the middle of the chip.

The Apple II and II Plus 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 RAM rows are C, D and E, with row C frontmost, and the six ROM sockets sit above them. Work one row at a time.

Apple II and II Plus

• The memory configuration blocks at D1, E1 and F1 are 14-pin jumper blocks, not ICs. They strap each RAM row into the memory map, and all three must be strapped identically. Clean them and refit them the same way round: a swapped or missing block gives a machine that boots to garbage or reports the wrong memory size.
• The 74LS138 at F12 selects the individual ROMs. If all the ROMs appear dead, suspect it before the ROMs.
• The 4116 16K RAM chips need +12 V and −5 V as well as +5 V, so a missing or sagging −5 V or +12 V rail shows up as a memory failure. Check the rails before pulling RAM.
• Do not fit 2716 EPROMs in place of the mask ROMs without adapting them. Apple says the ROMs resemble 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 6502 is at B4; the MMU at D4, the IOU at D6 and the HAL at D1; the video ROM at F4, the two main ROMs (CD and EF) at D8 and D10, the keyboard ROM at D12 and the AY-3600 keyboard decoder at D14. The eight 64K × 1 DRAMs occupy F6-F13.
• The MMU, IOU and HAL are custom parts: static-sensitive and the hardest to replace.

Internal cleaning

Dust traps heat and holds moisture against the board.

For routine dust removal, blow the board out with compressed air held at an angle, working from the top down, and paying attention to the gaps between the expansion slots.

A heavily contaminated board can be washed:

1. Remove all socketed ICs and store them in anti-static foam.
2. Wash the board with warm water and a little detergent, using a soft brush.
3. Rinse with distilled water.
4. Shake out the water from the sockets and from under components, then flush with 99% isopropyl alcohol to displace what is left.
5. Let it dry completely in a warm, dry place before refitting chips or applying power. Water trapped under a socket corrodes it.

Do not wash the keyboard or anything with a sealed switch or a paper label.

Keyboard

Remove keycaps with a keycap puller, wash them in warm soapy water and dry them fully before refitting. For a sticky or dead switch, work 99% isopropyl alcohol into it, operate it repeatedly, and let it evaporate before testing.

The Apple II and II Plus keyboard uses an MM5740 keyboard decoder, buffered by a 7404, feeding 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, with the repeat rate set by R3, 220 kΩ. The IIe uses an AY-3600 decoder at D14. Both decoders are static-sensitive and hard to source. Apple's service manual has a keyboard and keyswitch identification appendix for the II and II Plus.

Case cleaning

Clean the case with warm water and a little washing-up liquid on a soft cloth, cotton swabs around the logo and vents, then rinse and dry.

• Do not use household bleach. Sodium hypochlorite is no remedy for the yellowing of these cases, and it gives off chlorine if it meets an acidic or ammonia-based cleaner.
• Avoid silicone furniture polish, which leaves a residue that is hard to remove before retrobrighting or painting.
• Isopropyl alcohol removes adhesive residue and ink. Melamine foam is an abrasive and dulls a textured finish if pressed hard. Test anything on a hidden area first.

For yellowed cases, see Retrobrite.

Expansion slots

The Apple II, II Plus and IIe have eight peripheral slots, numbered 0 to 7 (the IIe replaces slot 0 with the auxiliary connector). Oxidised slot contacts stop cards working.

For each slot, spray contact cleaner into it, insert and withdraw a spare card several times, and let the cleaner evaporate before fitting cards. Clean card edge connectors with isopropyl alcohol and a lint-free cloth, or a pencil eraser for heavier oxidation, and brush off the crumbs. Do not use abrasive paper or a fibreglass pen on gold fingers: the plating is very thin.

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 does nothing with one card in may have that card holding INH low.

Power supply

The Apple II power supply is an Apple design, U.S. Patent 4,130,862, built by Astec. Read the electrical safety section above before working on it.

Apple's specification

Apple II power supply (Apple II Reference Manual, p. 92)

Parameter	Apple's figure
Input voltage	107-132 V AC, or 214-264 V AC (switch-selectable on supplies with 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)

The nominal "+12 V" rail is +11.8 V and the "−5 V" rail −5.2 V, so a supply reading 11.85 V is on specification. Apple gives no tolerance for the Apple II and II Plus rails in the Reference Manual or the Astec package. For the IIe, Apple does: Table 7-2 of the Apple IIe Reference Manual gives +5 V ±3%, +11.8 V ±6%, −5.2 V ±10% and −12 V ±10%, with the same current ratings and 60 W continuous, 80 W intermittent.

Voltage checks

Measure at the motherboard power connector with the machine running and a representative set of cards fitted. For the II and II Plus, which have no Apple tolerance, a useful bound for +5 V is the range the logic on the board is specified for: 74LS-series TTL is rated for 4.75 V to 5.25 V. Aim for 5.00 V. Compare the other three rails with Apple's nominals, and investigate a rail that visibly moves when a drive spins up. If a supply reads correctly on a DC meter but the machine still crashes, look at the rails with an oscilloscope for switching noise from a dried output capacitor.

Load testing

The supply can be tested off the machine, but it needs a load on its outputs. From Apple's rated currents:

Dummy load for about half of Apple's rated current

Rail	Nominal	Rated current	Resistor	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

Use resistors rated at least twice the calculated dissipation, mount them clear of anything flammable, and do not leave the test running unattended.

If one output is short-circuited, a feedback circuit stops the oscillator and cuts all outputs; the supply pauses for about a second and then tries to restart, repeating until the short is removed. That is the Apple II's tick-tick-tick: the supply is protecting itself against a load fault. Pull every card and disconnect the drives before condemning it.

Apple's later replacement supply (661-0455) is 1.5 inches longer than the original and fits any Apple II or II Plus. If it fouls the speaker, Apple's procedure moves the speaker about an inch back on the base pan with contact cement; if its mains cable is too short to reach, the procedure pulls more cable through the strain relief.

Visual inspection

With the supply open, check:

• the class-X mains capacitor (C1, 0.1 µF) for crazing, cracks, swelling or brown staining of the epoxy;
• the secondary electrolytics for bulging or leakage;
• the board around the switching transistor and secondary rectifiers for burn marks or discolouration;
• the output connector for corrosion;
• the inrush thermistor (R1) and the mains varistor (VDR1, 260 VAC) for cracks.

Capacitor replacement

Apple's Astec component listings give the values. For the AA11040B:

Astec AA11040B (Apple component listing, pp. 14-15)

Reference	Value	Notes
C1	0.1 µF 250 V AC	Metallised, class-X across the mains
C3, C4	2200 pF 400 V AC	Ceramic, class-Y
C5, C6	47 µF 250 V	Primary reservoir electrolytics
C7	220 µF 10 V	Electrolytic
C12, C13, C14, C19	1000 µF 10 V	Electrolytic
C15, C16	220 µF 10 V	Electrolytic
C20	680 µF 16 V	Electrolytic
C21, C22	330 µF 16 V	Electrolytic
C24, C25	47 µF 250 V	Electrolytic
F1	2.75 A 125 V	Fuse
VDR1	260 V AC	Varistor
R1	4 Ω or 5 Ω	Inrush thermistor

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

Order of work:

1. The class-X capacitor first. Replace it with a current X2-rated part of the same value. Once replaced, it needs no scheduled replacement.
2. The primary reservoir capacitors next. A dried 47 µF 250 V part makes the supply unstable under load.
3. Then the secondary electrolytics, using 105 °C low-ESR types.

ROM and RAM identification

ROM sockets

The six ROM sockets are identified by the address each covers: D0, D8, E0, E8, F0 and F8. The F8 (monitor) ROM sits at board location F3.

On an Apple II with Integer BASIC:

• Integer BASIC occupies E0, E8 and F0, and those ROMs also hold the Mini-Assembler, the Floating-Point Package and the SWEET-16 interpreter.
• F8 holds the monitor (the original Monitor or, later, the Autostart ROM).
• The Programmer's Aid #1 ROM goes at D0. D0 and D8 may be empty; that is not a fault.

On an Apple II Plus:

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

The Apple IIe has two main ROMs, CD and EF, plus a video ROM at F4. Apple's layout drawing puts the CD ROM at row 8 and the EF ROM at row 10, CD to the left of EF seen from the front; the community guide has them the other way round. Check the part number on the chip before replacing it.

RAM

The Apple II and II Plus take three rows of eight RAM chips, rows C, D and E. Each row must hold eight of the same type; different rows may differ.

• 4K parts are the 4096 type, marked MK4096 or MCM6604.
• 16K parts are the 4116 type, marked MK4116 or (as Apple prints it) UPD4160.

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

The Apple IIe has 64K as standard in eight 64K × 1 DRAMs at F6-F13, and 128K with an auxiliary-slot card.

On-board voltage regulation

There is none. The Apple II, II Plus and IIe main boards take all four rails straight from the supply, which regulates them itself by comparing the +5 V output against a reference and adjusting its oscillator. There are no 78xx or 79xx regulators and no regulator heat sink on these boards. A wrong rail at the board means a fault in the supply, the connector, or something on the board loading the rail.

Preventive checklist

1. Measure and note the four rails at the motherboard connector, so later readings have something to compare with.
2. Open the case and clean the interior.
3. Reseat the CPU, the ROMs, the memory configuration blocks and the F12 ROM decoder.
4. Inspect the supply's class-X capacitor and secondary electrolytics.
5. Clean the expansion slots and card edges.
6. Take batteries out of any peripheral cards before storing the machine. See Battery Explosion, Capacitor or Corrosion Damage.

Returning a stored machine to service

1. Inspect for rodent damage and for corrosion, especially around battery holders on cards.
2. Clean and reseat the chips.
3. Test the supply on a dummy load before connecting it to the motherboard.
4. Power up with no cards fitted, then add cards one at a time.
5. Run the Apple II diagnostics to check the machine.

Store the machine dry, out of direct sunlight, with dust covers, and supported so the board does not flex under the weight of cards.

Troubleshooting

Apple's troubleshooting chart

Apple's service chart for the Apple II lists probable causes in order of likelihood; check or replace them in that order.

Apple II Troubleshooting Chart (Apple, rev. Sep 82)

Symptom	Probable causes, in order
Will not boot; drive comes on	RAM row E; RAM on the Language Card at E2; motherboard
Programs run erratically, often crash	RAM; motherboard
No beep and no message; random characters on screen at power-on; drive does not come on	RAM row C; "F8" ROM at F3 on the motherboard; "F8" ROM on the Language Card at E2; motherboard
Peripheral does not work properly	Motherboard
Keys give the wrong character in the diagnostic's keyboard test	Keyboard cable; keyboard electronics; keyboard mechanism; motherboard
Applesoft or Integer BASIC fails or is erratic	ROM; motherboard
Game I/O port malfunction (check with the diagnostic)	Game paddles; motherboard
All video malfunctions (graphics and text)	Motherboard
Cassette interface malfunction	Motherboard
System dead: no beep, no video, no power light	Power supply; motherboard
System dead: no beep, no video, power light on	Power supply; motherboard
Speaker malfunction	Speaker; motherboard
No video display	Video cable; video pot adjustment; motherboard

Apple's chip swapping chart

Apple's chart names the chips to swap, by board location, for each symptom. It is for the Apple II and II Plus main board.

Apple II Chip Swapping Chart (Apple, rev. Sep 82)

Symptom	Location and chip type
Dead system (power-on light lit)	A2 74LS00, B1 74S174, B2 74S86, B13 74LS02, C1 74LS153, C2 74LS195
No RESET or no response	A13 555, B5 74LS174, B6 74LS257, B7 74LS257, B8 74LS174, B11 74LS08, C14 74LS32, E11-E13 74LS153, F12 74LS138, F13 74LS138, F14 9334, H1 74LS08, H3-H5 8T97, H8 6502, H10-H11 8T28, H14 74LS251
Apparent ROM problems	F12 74LS13, H1 74LS08
Apparent RAM problems	A2 74LS00, B5 and B8 74LS174, C14 74LS32, D2 74LS20, E2 74LS139, E11-E13 74LS153, F2 74LS139, H1 74LS08
No video (speaker does beep)	A2 74LS00, A8 74LS257, A9 74LS151, A10 74LS194, B2 74S86, B10 74LS74, B13 74LS02, C2 74LS195, C11 74LS04, D11-D14 74LS161
No text mode	A3 74166, A5 1513, A8 74LS257, A9 74LS151, A10 74LS194, B2 74S86
HIRES or LORES problem	A0 74LS194, A8 74LS257, A9 74LS151, A11 74LS74, B4 and B9 74LS194, B10 74LS74, C11 74LS04, C12 74LS257, F14 9334, H1 74LS08, J1 74LS257
Dark screen	A2 74LS00, B1 74LS174, B2 74S86, C1 74LS153, C2 74LS195
V or H sync fails	C13 74LS51, C14 74LS32, D11-D14 74LS161
Wrong page or video mode	B5 and B8 74LS174, B11 74LS08, B12 74LS11, B13 74LS02, C11 74LS04, C12 74LS257, E11-E13 74LS153, E14 74LS283, F2 74LS139, F14 9334, H1 74LS08, J1 74LS257
Wrong or bad characters	A3 74166, A5 1513, B5 and B8 74LS174, B6 and B7 74LS257
Bad cursor	A3 74166, B2 74S86, B11 74LS08, B13 74LS02
Bad graphics	A8 74LS257, A9 74LS151, A10 74LS194, A11 74LS74, B4 and B9 74LS194
No colour	B12 74LS11, B13 74LS02, C13 74LS51
Game paddles problem	F13 74LS138, H13 558, H14 74LS251
Cassette loading problem	F13 74LS138, H14 74LS251, K12 741 op amp
Cassette saving problem	F13 74LS138, K13 74LS74
Speaker problem	F13 74LS138, K13 74LS74
Keyboard problem	A12 74LS02, B6 and B7 74LS257, B10 74LS74, C11 74LS04, F13 74LS138
Peripheral card in a slot will not work	H2 and H12 74LS138

Apple's chart prints the character generator at A5 as "1513"; the Reference Manual describes it as a type 2513 character generator at A5. It prints H14 as "74LS5251" in the first entry and "74LS251" elsewhere.

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 try again.
2. If it still ticks with nothing connected, the fault is in the supply or on the motherboard.
3. If it now starts, add the cards back one at a time to find the one that loads it.
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 that the 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.
4. Check whether any card is pulling INH low.
5. If text is garbled but graphics are fine, reseat the character generator at A5.

Video problems

All timing on the board comes from the 14.318 MHz master oscillator, which also gives 7.159 MHz, the 3.58 MHz colour reference and the two 1.023 MHz clock phases. If the machine runs but video is unstable, check that oscillator. The 14 MHz and colour-reference signals are not on the peripheral connectors (except COLOR REF on slot 7), so a card cannot be the source of a fault in them.

Keyboard problems

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

Disk drive problems

Apple's preventive maintenance for the Disk II: clean the read/write head and the guide rails with isopropyl alcohol whenever the drive is serviced, and do not grease the rails; replace the mechanical assembly if the head ceramic shows worn or dull spots or the carriage binds; replace a worn or dirty head load button; and check the motor drive belt for cracks, slipping and lost elasticity. Check the cable and its orientation, and clean the controller card's edge connector. See Disk II and Floppy Drive Repair.

Tools

• Digital multimeter
• Anti-static mat and wrist strap
• IC extractor
• 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
• For deeper work: an oscilloscope (the fastest signal on the board is the 14.318 MHz master clock), a logic probe, an EPROM programmer (remember the ROM chip-select polarity), and an ESR meter

See Recommended Tools.

Related pages

• Apple II
• Apple II Plus
• Apple II Reference Manual
• Apple Astec Power Supplies Service Package
• Battery Explosion, Capacitor or Corrosion Damage
• Capacitor Failure Symptoms
• Retrobrite