Disk II
| Disk II | |
|---|---|
 |
|
| Two Disk II drives (All About Apple museum, CC BY-SA 3.0) | |
| Manufacturer | Apple Computer, Inc. |
| Type | 5.25-inch floppy disk drive |
| Release date | July 1978 |
| Price | US$495 with controller card if ordered before stock arrived; US$595 thereafter |
| Interface | 20-pin ribbon cable to the Disk II controller card |
| Compatible | Apple II, Apple II Plus, Apple IIe, Apple IIGS |
| Part number | Mechanical assembly 661-92012; analog card 661-92001 (Apple service parts) |
| Media | 5.25-inch single-sided diskettes, 35 tracks |
The Disk II Floppy Disk Subsystem is Apple's 5.25-inch floppy disk drive and controller card for the Apple II, designed by Steve Wozniak. It became available in July 1978 with DOS 3.1, the first full version of Apple DOS, at US$495 including the controller card for customers who ordered before Apple had stock, and US$595 otherwise.[1] Each controller card runs two drives.[2]
Origin
[edit | edit source].jpg)
At Apple's executive meeting in December 1977, Mike Markkula put a floppy disk drive at the top of the company's goals; his checkbook program took two minutes to load from cassette and another two for its data. Steve Jobs asked Shugart Associates for drive mechanisms without the usual read/write electronics, head load solenoid, track zero sensor or index hole sensor. Shugart called these stripped-down units the SA390 and supplied 25 prototypes. Apple engineer Cliff Huston made the analogue electronics work reliably and wrote the adjustment procedures for the production line.[1]
Wozniak's controller replaced the 40 or so chips of the S-100 controllers of the time with nine, later eight when two 555 timers were replaced by one 556. He first raised the FM format from nine sectors per track to ten, then moved to group coded recording at thirteen sectors, giving a formatted capacity of 113K, 23K more than Shugart's own figure. Early production was two people building about thirty drives a day. Within a couple of years Apple had Alps Electric design a cheaper version of the mechanism.[1] Apple's parts list for the drive carries write-protect actuators for both the Alps and the Shugart mechanisms.[3]
Format and capacity
[edit | edit source]| Software | Sectors per track | Capacity per side |
|---|---|---|
| DOS 3.1 to 3.2.1 | 13 | 116,480 bytes (113K); Apple: "over 116,000 characters" |
| DOS 3.3 (August 1980), Apple Pascal | 16 | 143,360 bytes (140K) |
All formats use 35 tracks of 256-byte sectors on one side of the diskette.[4][2] The move to 16 sectors with DOS 3.3 did not change the drives: only the ROM on the controller card was replaced, as part of the DOS 3.3 upgrade.[4] The Apple III kept the same 35-track, 16-sector disk format.[4]
Connecting the drive
[edit | edit source] | A wrongly fitted ribbon cable can damage the drive. Apple's application note: "If the cable from the disk drive to the controller card is not plugged into the controller's printed circuit card correctly, considerable physical damage can be done to the disk drive unit and its electronics", and on its warning page, "YOU CAN PERMANENTLY DAMAGE THE DISK DRIVE IF YOU ATTACH THE CABLE INCORRECTLY."[2] |
Apple's rules:[2]
- The cable leaves the connector on the side away from the card. If the cable has to be jammed between the connector and the card, it is the wrong way round.
- Every pin must go into its matching hole. Apple names failing to centre the connector as one possible error.
- Plug the cable into the controller card before putting the card into the computer, so that you can see the pins go in.
The first drive goes on the upper set of pins on the controller, marked DRIVE 1; a second drive goes on the lower set.[2]
Apple's application note also says that the DOS COPY program works only if the speeds of the two drives are matched to "something like one-half of one percent", even though every drive Apple shipped was within its speed tolerance.[2]
Service
[edit | edit source]Apple's Disk II Technical Procedures (rev. Feb 87) treat the drive as three exchangeable modules, the interface cable, the analog card and the mechanical assembly, plus a few parts and the four socketed ICs on the analog card.[3]
Symptom chart
[edit | edit source]| Symptom | Corrective action, in Apple's order |
|---|---|
| Drive comes on but will not boot; I/O errors in normal use | Clean the read/write head; adjust DSPEED; exchange the interface cable; the analog card; the mechanical assembly |
| Drive will not boot; drive does not come on | Exchange the interface cable; the mechanical assembly; the analog card |
| High-pitched whining | Exchange the mechanical assembly |
| Writes when the diskette is write-protected | Adjust the write-protect switch; exchange the analog card; the mechanical assembly |
| Reads but does not write | Exchange the analog card |
When swapping modules, Apple's method is to fit a known-good module, and if the fault remains, refit the original before trying the next one. Run Apple's 5.25-inch Disk Drive Diagnostic as the final check.[3]
Analog card
[edit | edit source]Apple's analog card test puts the suspect card on a known-good mechanical assembly connected as drive 2, with a known-good drive 1 and the controller in slot 6. Inspect the card first. Burned or melted ICs can be replaced; a card with a damaged socket, or with a burned or exploded C4 (the large capacitor at the corner of the card) or other damaged components, went back to Apple. Do not clean the gold contacts with an eraser: use a liquid or spray contact cleaner and a clean cloth.[3]
| Test | Symptom | ICs (location and type) |
|---|---|---|
| Card on drive 2, boot from drive 1 | Drive 1 will not boot | D4 2003, B4 74LS125, A3 CA3146, B1 3470 |
| DSPEED diagnostic | Speed indicator does not respond to the adjustment | B1 3470, A3 3146, B4 74LS125, D4 2003 |
| CATALOG,D2 | Head does not move | D4 2003 |
| Disk does not turn | D4 2003 | |
| Drive recalibrates repeatedly | B1 3470 | |
| I/O ERROR | B1 3470, A3 3146, B4 74LS125, D4 2003 | |
| UNLOCK HELLO on drive 2 | File will not unlock | B4 74LS125, D4 2003, A3 3146 |
| Write-protected diskette on drive 2 | No WRITE PROTECT ERROR | B4 74LS125 |
Replace the chips one at a time, skipping any already replaced, and repeat the test after each. If all four have been replaced and the fault remains, refit the original ICs; Apple's instruction was to return the card.[3]
Adjustments
[edit | edit source]- Drive speed (DSPEED): run the DSPEED test of Apple's 5.25-inch Disk Drive Diagnostic from a known-good drive 1, with the drive to be adjusted as drive 2 and its cover off. The adjustment is the potentiometer on the motor control board at the back of the mechanism, not the potentiometers on the analog card. Keep the drive flat, turn the screw very slowly, and set the speed within the "good" range and as close to 0 as possible. A drive that cannot be brought into range needs a new mechanical assembly.[3]
- Write-protect switch: with a scratch diskette fully inserted and the door open, set the switch with its two setscrews (the far one is the pivot, the near one sets the position) so that it is disabled with the diskette fully in and enabled with the diskette withdrawn about an inch.[3]
Preventive maintenance
[edit | edit source]Apple's procedure, to be done whenever the drive is serviced:[3]
- Remove the case and the analog card.
- Clean the head guide rails with isopropyl alcohol (80 % alcohol, 20 % water). "Do not use grease."
- Inspect the head for worn or dull spots in the ceramic; if there are any, replace the mechanical assembly.
- Clean the head with isopropyl alcohol on a cotton swab.
- Move the head assembly along its full travel by hand and check for blockage or friction; if there is any, replace the mechanical assembly.
- Replace the head load button if it is worn or dirty. Some buttons are glued in; Apple sent those assemblies back for service.
- Check the motor drive belt for cracks, slippage and loss of elasticity, and replace it if it is dry, cracked or slipping.
The analog card's two front screws can be either standard or metric thread; keep them with the drive they came from.[3]
Parts
[edit | edit source]| Part | Apple part number |
|---|---|
| Mechanical assembly | 661-92012 |
| Analog card | 661-92001 |
| Disk II cable assembly, 15 inch | 590-0031 |
| Drive belt (Disk II and Disk III) | U880-0002 |
| Load button | U815-0064 |
| Collet hub | U815-0067 |
| Write-protect switch | U705-0005 |
| Write-protect actuator, Alps mechanism | 815-0377 |
| Write-protect actuator, Shugart mechanism | U815-0073 |
| Door and hinge assembly | U815-0066 |
| ICs: 2003A, MC3470, 3146, 74LS125 | 327-2003, 355-3470, 351-3146, 306-0125 |
DuoDisk
[edit | edit source]Apple describes the DuoDisk as "effectively two disk drives in one case", both attached to a single analog card, with the left-hand drive as drive 1. Its analog card carries a different set of chips from the Disk II card and has its own chip-swapping chart.[5] Read the engineering number on the card first: symptoms 1 to 4 apply only to cards numbered 676-[ ]101, and symptom 5 to 676-[ ]101 and 676-[ ]102.[5]
| Symptom | Location and chip, in Apple's order |
|---|---|
| 1. Motor runs but the LED is off; will not boot | A1 3469, B4 74LS32, B5 74LS07 |
| 2. Motor and LED on; will not boot | B1 CA3141, B3 74LS125, A1 MC3469, C1 MC3470, B2 74LS33, B5 7407, C3 74LS74, C4 74LS02, C6 ULN2068, C7 ULN2068 |
| 3. Reads but does not write | A1 MC3469, B1 CA3141, B2 74LS33, B3 74LS125, C5 74C86, B5 7407 |
| 4. Writes to write-protected diskettes | A1 MC3469 |
| 5. Data damaged when rebooting with Open Apple-Control-Reset, or with some copy-protected software, on a unit that passes the Drive Acceptance Program | Capacitors C29 (A1) and C30 (B1): remove both, do not replace |
Before replacing any chip, Apple says to inspect the card for melted or broken components, "particularly the 74LS125 and C21. If you notice fuzz on the card, return the card to Apple. This usually means that the card was connected to a computer with the power on, and capacitor C21 has exploded."[5] Connect and disconnect a DuoDisk only with the computer switched off.
Related pages
[edit | edit source]- Apple II
- Apple II General Maintenance
- Apple Floppy Disk Drive
- Floppy Drive Repair
- Recommended Tools
- Apple Disk II Technical Procedures
References
[edit | edit source]- ↑ 1.0 1.1 1.2 Steven Weyhrich, Apple II History, chapter 5, "The Disk II", apple2history.org, retrieved 2026-10-01.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Apple Computer, Disk II Floppy Disk Subsystem Installation and Operating Manual, 030-0011-00, 1978, Introduction (capacity; DRIVE 1 and second-drive pins; centring the connector) and Disk II Application Note, 30 July 1978, pp. 34–35 (cable fitting; COPY speed matching; warning page). Hosted as File:Apple Disk II Floppy Disk Subsystem Installation and Operating Manual.pdf.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 Apple Computer, Disk II Technical Procedures (rev. Feb 87), from Apple Service Technical Procedures: Apple II/Apple III Archived Products, Volume One (072-0231): take-apart pp. 1.3–1.6; symptom chart p. 2.3; analog card troubleshooting pp. 2.4–2.8; adjustments pp. 3.3–3.5; preventive maintenance pp. 4.2–4.4; illustrated parts list pp. 5.3–5.7. Hosted as File:Apple Disk II Technical Procedures.pdf.
- ↑ 4.0 4.1 4.2 Steven Weyhrich, Apple II History, chapter 15, "DOS 3.3 & Beyond", apple2history.org, retrieved 2026-10-01: DOS 3.3 in August 1980, 16 sectors and 140K, controller ROM change only; DOS 3.0 to 3.2.1 timeline; Apple III and Pascal disk format.
- ↑ 5.0 5.1 5.2 5.3 Apple Computer, DuoDisk Technical Procedures, Section 1, Troubleshooting (rev. Aug 85): general information p. 1.2, card inspection and engineering numbers p. 1.4, chip swapping chart p. 1.5. Bound in the Apple Service Support Training Programs binder described at Service Support Training Programs LaserWriter Technical Procedures Jan 1985 (PDF, PDF pp. 165–170).