Commodore 1541 Floppy Disk Drive — Newtronics Mechanism — For Parts/Repair

Condition: For parts or not working. Sold as-is with a known speed-control fault on the analog board. See full description below.

What's included:

• Commodore 1541 floppy disk drive (Newtronics-Mitsumi mechanism)
• Original cream/beige plastic case with green activity LED
• Original 1540/1541 analog board (Commodore part number 251854 REV A)
• Original Mitsumi spindle motor and Newtronics mech assembly

NOT included: No IEC power cable, no serial cable, no original box, no manual.

The fault

The drive powers on and the controller responds to host commands. The 1541 built-in diagnostic test boots and the head steps through all 40 tracks reporting data without crashing.

However, the spindle motor runs at 555 RPM — well above the 300 RPM spec. This likely points to a fault in the speed-control sub-PCB, though we have not opened the unit to confirm. Possible causes include the VR1 trim pot drifted out of spec, an issue with the tach response path, or a problem with the motor driver stage (per the 1540/1541 Service Manual PN-314002-01). The drive cannot read or write disks reliably until the speed is corrected.

Based on the diagnostic test, the controller board, head assembly, motor, and mech all appear to be functional — they just can't operate at the wrong RPM. We have not done component-level troubleshooting on the speed-control sub-PCB, so the exact cause has not been verified.

Parts of value

• Original case: Clean cream/beige plastic, original green activity LED intact, all four rubber feet present, flip-lever door mechanism intact. The plastic Commodore "C" badge that sits over the drive door is missing (cosmetic only, the drive functions identically without it). Minor scuffs and a small scratch on the top consistent with 40+ year old use. No cracks, no broken plastic, no yellowing of note. Photos show the actual condition.
• Back panel: Clean IEC C14 power inlet, working rocker power switch ("I-on" / "O-off"), fuse holder (with spare fuse holder next to it), two DIN-5 IEC serial ports for daisy-chaining. No rust, no bent tabs, no damage.
• Controller board (Commodore assembly 251854 REV A): Boots the diagnostic test, responds to host, head stepping works through all 40 tracks. Chip set: 6502 CPU, 6522 VIA x2, 6532 RIOT, 2332 DOS ROM, 2364 character ROM, MN4216-20 Matsushita RAM, 74LS logic.
• Head assembly:The head has not been independently read-tested due to the speed fault, so a buyer should retest after repair.
• Newtronics-Mitsumi mech: Belt-driven spindle with Mitsumi DC 12V motor (visible on motor label "DC 12V / MITSUMI").
• Power supply (transformer + analog board regulators):Two Nichicon 6800µF 25V filter caps on the analog board are visibly intact (no bulging, no leaks).

What's wrong (parts to repair or inspect)

• Speed-control circuit on the dedicated Newtronics speed-control sub-PCB. The most likely culprit is the VR1 trim pot (speed adjustment) drifted out of spec. VR1 is visible and accessible on the sub-PCB, and a non-metallic screwdriver adjustment is a no-cost first thing to try — the 1541 built-in diagnostic test can be used to monitor the speed while adjusting. If VR1 adjustment does not bring the speed back to spec, other possibilities to investigate include an open solder joint on the tach response path or a failed driver transistor. The 1540/1541 Service Manual covers the relevant troubleshooting paths.

Provenance and production

This drive was manufactured in Hong Kong at the Commodore factory. The FCC ID label on the back reads BR96081541. The controller/analog board assembly is Commodore 251854 REV A. The Newtronics-Mitsumi mech dates from the 1985-1986 production run. Factory QC stickers ("PASS" and "NI BURN") are still visible on the mech chassis.

Shipping

Ships via USPS Ground Advantage. Lower 48 US states only Tracking is included. Item will be shipped within 2 business day of payment.