Apple Floppy Disk Drive: Difference between revisions

| image = [[File:Apple Floppy Disk Drive.jpg]]

| caption = Macintosh 800K External Drive (Model M0131)

| manufacturer = Apple Computer, Inc. (Sony mechanism)

| compatible = Macintosh Plus and later; see below

The '''Macintosh 800K External Drive''' (model M0131) is Apple's double-sided 800 KB external 3.5-inch drive. It reads and writes both '''800 KB double-sided and 400 KB single-sided''' floppies.<ref name="gmfh9">''Guide to the Macintosh Family Hardware'', second edition, Apple Computer, Inc. / Addison-Wesley, 1990 — hosted on this wiki as [[:File:Apple Guide to the Macintosh Family Hardware 2nd Edition 1990.pdf]]. Chapter 9, "Floppy Disk Interfaces": the description of the 400K drive as a single-sided version of the Apple 800K drive; Table 9-1, drive type against disk type, capacity, file system and encoding method; the GCR/NRZI and MFM encoding rules; Tables 9-2 and 9-6, which Macintosh models take which drive and how many internal and external drives each supports; the IWM and SWIM interface ICs, their C8M (7.8336 MHz) and C16M (15.6672 MHz) clocks, the maximum data rate of approximately 500 kbit/s and the effective GCR rate of approximately 375 kbit/s; Figure 9-3 and Tables 9-3 and 9-4, the 20-pin internal connector pinouts; Figure 9-4 and Table 9-5, the '''DB-19''' external connector pinout; the warning that all devices connected to a Macintosh Plus must not draw more than 600 mA at +12 V, 700 mA at +5 V and 10 mA at −12 V, that a single-sided floppy drive requires 500 mA at +12 V and 500 mA at +5 V and that an Apple 800K drive requires 600 mA at +12 V and 360 mA at +5 V; the PWM motor-speed-control line, used only by 400K single-sided drives and generated by a PAL on the Macintosh Plus and the BBU on the Macintosh SE from values in the disk-speed buffer in RAM, with the statement that the 800K drive controls its own motor speed and ignores the signal; the statement that '''the SWIM does not support the single-sided floppy disk drive'''; the statement that an external 800K drive may be connected to any model that supports an external FDHD drive; and the Hard Disk 20 pass-through arrangement, whose DB-19 pinout is identical to the computer's.</ref>

The interface IC is the '''IWM''' (Integrated Woz Machine). It converts between the NRZI serial data used to talk to drives and the 8-bit parallel data used by the CPU; the Disk Driver software converts between GCR and ordinary bytes.<ref name="gmfh9" />

The IWM's clock is '''C8M, 7.8336 MHz''' on the Macintosh Plus and earlier, and '''C16M, 15.6672 MHz''' on the Macintosh SE and II — twice as fast. During startup, software sets a bit in the IWM to divide the faster clock by two when using the 800K drive, the single-sided 400K drive or the Hard Disk 20.<ref name="gmfh9" />

Maximum data rate to the drive is approximately '''500 kbit/s'''; because four bytes of GCR correspond to three bytes in RAM the '''effective maximum is about 375 kbit/s'''.<ref name="gmfh9" />

== It Controls Its Own Speed ==

This is the structural difference from the [[Apple 400K Drive|400K drive]]: '''the 800K drive controls its own motor speed and ignores the PWM speed-control signal''' on pin 10 of the connector.<ref name="gmfh9" /> The 400K drive depends on that signal being generated by the host.

Because of that, the 800K drive works on machines that provide no speed-control line — and Apple states explicitly that '''on all Macintosh models that support an external FDHD drive, you can connect an external 800K drive instead'''.<ref name="gmfh9" /> That makes the M0131 the most widely compatible external floppy drive Apple sold.

| Macintosh II || 1 or 2 || 0 — '''no external floppy connector'''

Plus, per the note above, any model that supports an external FDHD drive.<ref name="gmfh9" />

On the Macintosh Plus and SE the external connector also accepts a 400K drive or an Apple Hard Disk 20; the Hard Disk 20 has a pass-through DB-19 with an identical pinout so both can be used together.<ref name="gmfh9" />

'''An Apple 800K drive requires 600 mA at +12 V and 360 mA at +5 V.'''<ref name="gmfh9" /> The combined load of everything connected to a Macintosh Plus must not exceed '''600 mA at +12 V, 700 mA at +5 V and 10 mA at −12 V'''.<ref name="gmfh9" />

An 800K drive therefore uses the Macintosh Plus's '''entire''' +12 V allowance on its own. If you are chasing an intermittent fault on a Plus with several things plugged in, start here.

== The Apple 3.5 Drive Mechanism ==

 

The mechanism Apple later shipped as the [[Apple 3.5 Drive Service Source|Apple 3.5 Drive]] is the same family and is properly specified in its own Service Source, which is useful because the M0131's own manual is not:<ref name="ss35">''Apple 3.5 Drive Service Source'', Apple Computer, Inc. — hosted on this wiki as [[:File:Apple 3.5 drive.pdf]]. Specifications: disk diameter 3.5 in., 2 recording surfaces, 80 tracks per inch; seek time track-to-track 6 ms maximum, settle time 30 ms maximum, drive startup time 600 ms maximum; head position accuracy ±0.035 mm; formatted capacity 800K and unformatted 1,246K, with the note that disks should be certified double-sided media; the list of directly supported computers and the note that one additional drive can be daisy-chained on the Apple IIGS; operating temperature 40–122 °F (5–50 °C), storage ‒40 to 140 °F with no condensation, relative humidity 5–90%; electrical +12 V standby 10 µA, typical 120 mA, peak 600 mA during eject only for a 2-second maximum, and +5 V standby 10 mA, typical 360 mA; size 2.01 × 4.72 × 7.87 in. (51 × 120 × 200 mm) and weight 2.8 lb (1.3 kg). Troubleshooting symptom charts, including the yellow-versus-red logic-board-to-drive cable checks and the CXD1085A/CXD1085B daisy-chain gate-array revision.</ref>

| Seek time, track to track || '''6 ms maximum'''

| Settle time || '''30 ms maximum'''

| Drive startup time || '''600 ms maximum'''

| Head position accuracy || '''±0.035 mm'''

| +12 V || Standby 10 µA; typical 120 mA; '''peak 600 mA during eject only, 2 seconds maximum'''

== Two Faults With Non-Obvious Causes ==

These come from Apple's own symptom charts and are the kind of thing that costs hours if you do not know them.

 

'''If an Apple 3.5 Drive 800K mechanical assembly is being used as a Macintosh internal drive, the logic-board-to-drive cable must be YELLOW, not RED.'''<ref name="ss35" />

 

The related symptom is unmistakable: '''an internal 3.5-inch drive on a Macintosh Plus that ejects continuously''' — Apple's remedy is to "verify that cable has yellow stripe, not red stripe".<ref name="ss35" /> A drive that spits out every disk you feed it is almost certainly wearing the wrong cable, not failing.

 

'''Symptom:''' one or more Apple 3.5 drives are daisy-chained to a DuoDisk or to one or more UniDisk 5.25 drives, and the drives suddenly start to spin and can no longer be accessed by the [[Apple IIGS]].<ref name="ss35" />

 

'''Cause and fix:''' check the part number on the gate array on the '''daisy-chain interface board'''. If it reads '''CXD1085A''' that is a Revision A board; replace it with a Revision B board, '''CXD1085B'''.<ref name="ss35" />

An obscure but genuinely useful procedure from Apple's own manual. '''When an Apple 3.5 mechanism is installed in an 800K drive, you cannot eject a disk by holding down the mouse button during boot up.'''<ref name="ss800">''Apple 800K Drive Service Source'', Apple Computer, Inc. — hosted on this wiki as [[:File:Apple 800k drive.pdf]]. Take Apart: four screws in the bottom cover; a screw in the clamp holding the interface cable; two screws releasing the drive assembly from the cover and four holding the drive in its housing. Additional Procedures, "Restoring Mouse Eject": the procedure for an Apple 3.5 mechanism fitted in an 800K drive, and the identification of the wire to remove and insulate.</ref>

Apple's correction:<ref name="ss800" />

# Orient the cable connector as shown in the manual. Locate '''the last wire on the left side in the lower row'''; the pin above it is empty.

# Look at the bottom and locate the '''spring clip''' under that wire.

# '''Push in on the spring clip''' and gently pull the wire to remove it.

# '''Wrap the connector end of the wire with electrical tape''' to prevent electrical contact.

 

 

 

 

 

Four bottom screws distinguishes this drive from the [[Apple 400K Drive|400K drive]], which has six.

Apple's symptom charts for this family:<ref name="ss35" />

|+'''Symptom charts'''

| Drive does not come on; LED flashes once or does not light || If an Apple 3.5 Drive 800K mechanical assembly is fitted internally, '''verify the cable is yellow, not red'''; then drive mechanism, external drive cable, LED assembly

| Internal 3.5-inch drive on a Macintosh Plus ejects continuously || '''Verify the cable has a yellow stripe, not a red stripe'''

| Apple 3.5 drives daisy-chained to a DuoDisk or UniDisk 5.25 spin up and become inaccessible on an Apple IIGS || Replace a Revision A '''CXD1085A''' daisy-chain gate array board with Revision B '''CXD1085B'''

Note the ordering principle Apple uses throughout: '''cure in order of most likely first, and if a replaced module does not fix the symptom, reinstall the original before moving on'''.<ref name="ss35" />

=== Head cleaning ===

A 3.5-inch head-cleaning disk. Do not over-clean; the heads wear.

=== Will not eject ===

 

 

 

 

== Apple's DuoDisk chip-swapping chart ==

 

 

<templatestyles src="Template:StyledTable/styles.css" />

{| class="wikitable styled-table"

Apple qualifies the chart: symptoms 1 to 4 apply '''only''' to analogue cards with engineering number

'''676-[ ]101''', and a fifth symptom applies to 676-[ ]101 or 676-[ ]102. Find the engineering

number on the card first.<ref name="lwtp85" />

'''A self-inflicted fault with a named component.''' Apple: inspect the card for melted or broken

components before replacing any chip, "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'''." Do not hot-plug one of these

drives.<ref name="lwtp85" />

== See Also ==