Tech Flashback: Citizen 3.5″ Floppy Drive

I just managed to find an old Citizen drive that’s a bit borderline, and a head-clean didn’t help, so I thought I’d throw it out – but before I do that, I’ll open its guts for all to see.

This drive is manufactured by Citizen in China. It is a bezel-less drive from a Compaq Deskpro SFF PC. This drive is rated at 5v 936mA. It’s manufactured fully enclosed (unlike some other drives where the spindle is externally visible, and the top case is removable without screws). Removing the screws and taking the lid off, we can see the drive’s internals.

Visible is the tray which the floppy sits on, the plastic arm that levers open the protective door on the floppy. The heads are visible, separated due to the lack of a disc. Bottom right, we can see the track zero sensor, the stepper motor (which moves the head along the rail). In the top left, we see the flexible ribbon that connects the heads to the main-board in the back of the drive. From another angle …

… we can see the Track Zero sensor which is an optical type in this drive, interrupted by the metal plate attached to the head sled. In some other drives, it’s mechanical microswitch based. Upon inserting a floppy, the heads are loaded onto the disk like so:

Disassembling the drive further, we can see the controller board.

And the spindle motor, with controller. The spindle itself has a slightly springy nub which engages with the metal disk plate inside the 3.5″ disks. You can see the springy switches which detect density and write protect status.

Update: I managed to dismantle this further – so we get to see what’s inside the motor itself:

It is a three-phase motor, with three hall effect sensors. The spindle itself is surrounded by a flexible thick fridge-magnet like material on the outer edge, as the fixed magnet part of the motor. Since it wasn’t working properly anyway, I decided to take it all apart and dispose of it. So lets examine the head really closely.

We can see what appears to be the main head, flanked with two trailing tunnel erase heads. This was part of the floppy standards – the tracks are written slightly wider than they need to be, and then a guard band is erased around the edges of the track. This “improves interchangeability”. For those with more interest in various floppy formats – I found this web page which had further information which was quite interesting.

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