Commodore 1581 disk drive
3.5 in 800 KB MFM drive on an external brick. Reliable; the brick and the DOS ROM are the usual faults.
Open the Commodore 1581 disk drive in Retro Bench- Also
- 1581 board 250471 (schematic 252380 rev. 4)
- Year
- 1987
- CPU
- 6502A @ 2 MHz
- RAM
- 8 KB (8K × 8 SRAM)
- ROM
- 32 KB DOS 10 (23256 312558 or 27256 EPROM 318045)
- Video
- none
- Sound
- none
- OS
- Commodore DOS 10
Chips
| Chip | Where | Role |
|---|---|---|
| WD1770 / WD1772 floppy disk controller | U4 (WD1770, or WD1772 with J1 removed; $6000-$6003) | Single and double density floppy disk controller with built-in data separator and write precompensation. |
| MOS 8520 / 8520A CIA | U5 ($4000-$400F) | 1581 serial bus, fast-serial shift register, LEDs, device number, disk-change and motor lines |
| 6502 / 65C02 CPU | U1 (6502A 2 MHz) | CPU |
| 23256 mask ROM 32K x 8 | U2 (DOS 10: 312558 mask ROM or 318045 27256 EPROM; socketed) | 32K x 8 mask ROM in the 27256 pinout. |
| 7406 hex inverter buffer/driver (open collector) | U8, U12 | Serial bus line drivers (CLK, DATA, ATN acknowledge), stepper phase and LED drivers |
Ports and connectors
- Serial bus (IEC) in / out, DIN-6 × 2 (wired in parallel)
- Power in, 4-pin DIN socket (CN6)
- Power out to the mechanism (CN1), 4-pin 0.1 in SIL header
- Disk drive data cable (CN2), 34-pin dual-row header (Shugart-style)
Power rails
| Rail | Expect | Measure at |
|---|---|---|
| +5 V | About +5 V, steady under load | 6502 pin 8; 8520 pin 20; 1770 pin 15; 1581-power pin 1 (CN6) |
| +12 V | About +12 V | 1581-power pin 4 (CN6); CN1 to the mechanism |
Symptoms
- Random errors after warm-up, works cold
- Activity LED stays on after power-up, no access: check 23256, 8520
- LEDs flash a code at power-up: check 23256
- Directory corruption, intermittent FILE NOT FOUND: check 1770
- Intermittent DEVICE NOT PRESENT
- Mechanism dead or burned after reassembly
- Locks the bus on a C64 with a Datasette connected
- Power jack dead or intermittent