Shugart/Alps 5.25 in mechanism, a four-chip analog card and a 20-wire ribbon to an eight-chip controller in slot 6.
| Chip | Where | Role |
|---|
| ULN2003 / µPA2003 seven Darlington driver | D4 on the analog card (socketed, Apple 327-2003) | Seven-channel Darlington driver (stepper and motor drive) |
| MC3470 floppy disk read amplifier | B1 on the analog card (socketed, Apple 355-3470) | Read amplifier, peak detector and pulse shaper |
| 74LS125 quad 3-state buffer | B4 on the analog card (socketed, Apple 305-0125) | Drive-side 3-state gates: write protect, read data, write data, write request |
| CA3146E transistor array (write driver) | A3 on the analog card (socketed, Apple 351-3146) | Head write driver and write/erase current switch |
| P6 state-sequencer PROM 341-0028 (256 × 8, 6309 type) | B3 on the Disk II Interface Card, marked PROM P6 | Logic state sequencer program (the "state machine") |
| P5 boot PROM 341-0027 (256 × 8, 6309 type) | D3 on the Disk II Interface Card, marked PROM P5 | Controller boot code at $Cn00-$CnFF |
| 74LS323 8-bit universal shift/storage register | C3 on the Disk II Interface Card | Controller data register (shifts disk bits in and out) |
| 74LS259 8-bit addressable latch (9334) | C2 on the Disk II Interface Card (9334, 74259 or 74LS259) | Controller soft switches $C080-$C08F,X: phases, motor, drive select, Q6, Q7 |
| 74LS174 hex D flip-flop | A3 on the Disk II Interface Card | Sequencer state latch and read-pulse synchronizer |
| Rail | Expect | Measure at |
|---|
| +5 V | +5 V (Sams: 5.0 V at C4 +) | 3470 pin 11; 74LS125 pin 14; disk2-ribbon pins 11, 12 |
| +12 V | +12 V nominal (Sams: 11.6 V at Q1 emitter) | 2003 pin 9; 3470 pin 18; disk2-ribbon pins 13, 15, 17, 19 |
| +12 V gated | About 11.6 V with the drive enabled; 0 V off | Q1 (MPSU51) collector; edge contacts 10, 11, 12 |
| -12 V | -12 V (Sams: -12.0 V at C5 -) | disk2-ribbon pin 9; C5 |
| Controller +5 V (switched) | +5 V only while a drive is on | P6 pin 20; 74LS174 pin 16 |