Service manual

OVERVIEW

The drive itself an independent memory device. THe drive is composed of a media clamp rotating

mechanism, a head positioning mechanism and an eject mechanism. All positioning operations,

excluding insertion and removal of diskettes, are controlled by the internal guide mechanism. Closing

the front door causes the media clamp mechanism to operate. Two operations are performed in the

following order:

The diskette is centered.

The diskette is clamped and retained between the spindle and the hub.

The spindle and hub rotates at 300 r.p.m. through a closed/loop control circuit employing a D.C

motor/tachometer. It is important that the relationship between the head and the media is maintained

correctly during operation. For this purpose, a pressure pad is used to hold and press down the

media (about 12g) from the opposite side of the head. This head assembly is coupled by a metal

band to a four base stepping motor which performs the track positioning. One step of the stepping

motor corresponds to a 1/2 track movement. The control circuit on the logic board selects the

direction and number of steps to the desired track.

The Read/Write head uses a glass-bonded, ferrite/ceramic head. Track-to-track erasing is

accomplished by the straddle erase method. The surface of the Read/Write head is mirror-ground to

minimize wear of the head and media. Also, the head is designed in such a way that the maximum

signal can be obtained from the media surface.

The spindle drive motor operates on 12 VDC and turns the spindle, through a belt drive, at 300

revolutions per minute. The speed of the drive motor is controlled by a feedback signal from a

tachometer, which is housed in the drive motor assembly. The feedback signal controls a servo amp

that supplies the 12 VDC drive current.

FLASH CODE

The 1541, upon power-up, goes through its own internal diagnostic. If an electronic problem is

detected, it's indicated by flash code. The led's will blink a number of times, pause, and then flash

again until the problem is corrected.

Number of flashes

Possible failure

Zero page

3,4

DOS ROM's

5,6,7,8

RAM

Circuitry associated with these components can also cause the failure code. Therefore, it should be

suspected as the next possible defect.