Epson SD320 (5.25 inch floppy drive) notes

Tony Duell ard at
Sat Mar 4 17:13:59 CST 2006

SD320, SD321 drive dismantling

Remove the logic board : 
Undo the 4 screws fixing the logic board. The rear left is a long machine
screw, rear right a short machine screw, centre right and front centre are
(short) self-tapping screws. Lift the logic board to disconnect the 3 pin 
connector at front left (index/write protect sensors), 10 pin 
(positioner)  and 3 pin (spindle motor) connectors at rear. Turn logic 
board over towards right side of the drive. Free the head cables from the 
clamps on the logic PCB, unplug the head connector. Set the logic board 

On SD320 (with head load solenoid), dismantle the head load mechanism :
Remove the screw and washer on top of the head load solenoid. Loosen the 
screw fro the rear bearing of the head load flap (this screw is on the 
left side of the drive chassis) until the bearing can be turned away from 
the pivot pin. Free the hard load flap from its front bearing, remove it, 
note how the compression spring fits over a peg on the base of the linear 
positioner.  Remove the conical spring from the top of the head load 
solenoid, remove the solenoid armature. Remove the screw and bearing 
(loosened earlier). Remove the screw holding the head load solenoid to 
the chassis, lift out the solenoid and 'stick' it to the linear 
positioner magnet. When reassembling this section, note that the screw on 
top of the solenoid should not be fully tightened. Adjust it so that the 
heads load correctly when the drive is tested on an exerciser.

Remove the linear positioner (voice coil assembly) :
Undo the 2 screws + springs and the single countersunk screw fixing the 
linear positioner to the main chassis. Free the head cables from the 
clips on the right-hand disk guide. Place a piece of paper between the 
heads, lift the positioner from the rear and slide it out

Remove the disk clamp :
Unhook and remove the tension spring for the frontpanel button linkage. 
Mark the position of the index sensor on the disk clamp bridge to aid 
reassembly. Remove the 3 screws holding the bridge in place, lift it up 
and turn it over towards the left side of the drive (take care not to 
damage the index phototransistor wiring. Remove the 3 spacers from the 
slots in the disk guides. Free the index phototransistor wiring from the 
hooks on the bridge, remove the screw holding the phototransistor mount 
in place and remove the bridge completely.

Remove the spindle motor and spindle : 
Remove the 2 screws holding the spindle motor in place. Remove the motor, 
slipping the belt off the pulley. Remove the belt from the idler and 
spindle. Remove the idler (one central screw, washer on top of bearing). 
Remove the central screw from the spindle hub, lift off the spindle hub 
and remove the bearings (crinkle washer under top bearing). If possible 
remove the washer from the fixed spindle in the chassis

Remove the front panel :
Remove the 2 screws and slide the panel out, taking care not to damage 
the index LED wiring.

Remove the disk guides : 
Remove the right hand disk guide (2 screws). Remove the index LED 
mounting (1 screw), then remove the screw holding the left hand disk 
guide. Remove the guide. Undo the screw holding the sensor PCB to the 
guide and remove it.

Dismantle the interlock lever : 
Unhook the tension spring from the eject linkage. Remove the E-circlip 
from one end of the interlock lever pivot, slide out the pivot rod and 
remove the lever. Recover the compression spring.


Dismantling the spindle motor 

Do NOT dismantle the spindle motor unless absolutely necessary. Most 
electronic repairs can be performed without dismantling the mechanical 
section. However, should it be necessary to dismantle it, proceed as follows.

Clean off the silicone rubber over the FG (frequency generator) coil 
wires. Try to avoid damaging the wires. Desolder them from the PCB pads.

Bend up the 4 tabs on the bottom of the motor and pull off the housing 
complete with the FG coil.

Support the motor on a bench vice with the pulley between the jaws. Using 
a hammer and pin punch, tap the spindle downwards until it is free from 
the rotor. Remove the rotor from the top of the motor. Remove the 
spindle, washer, and lower bearing. Push out the upper bearing.

If the FG wires were damaged when the cover was removed, carefully 
scrape away the tops of the 3 heat stakes retaining the coil former 
inside the housing. Pull out the former (and lower pole piece), and 
either unwind one turn to give a longer end of wire for reassembly, or 
re-wind the coil. Put the former back in place, if you have been careful 
in removing it, it will snap in place without further fixing.

Motor Protection Circuit : 
The circuit round Q33 removes the drive from the motor if the control 
voltage from IC10 rises too high (either because the motor is overloaded, 
or because the FG signal is missing). If this triggers too easily (the 
motor stops after a few seconds), decrease R76 to 56k


Dismantling the positioner

On an SD-320, desolder the head load solenoid leads from the positioner 
connector PCB and set the solenoid aside

Undo the PCB retaining screw and allow the PCB to move away from the rear 
of the positioner.

Undo the screw holding the graticule to the carriage. Remove the clamp 
plate under the screw, then with the heads fully 'out', free the 
graticule from the carriage and slide it out of the optical block. 

Straighten the end 2 tabs on the underside of the unit (these retain the 
cover on the velocity transducer). Remove the cover.

Remove the rear section of the voice coil core, which is retained by a 
single screw under the rear of the positioner.

Remove the 2 screws holding the voice coil and velocity transducer coil 
to the carriage. With the heads 'out', remove the pole piece from the 
middle of the velocity transducer coil (this is retained by magnetism only).

Retract the heads, then lift the coils off the carriage. Leave them 
hanging on the flexible PCB

Remove the clamps from the rear end of each head rail (1 screw each). 
Slide out the front clamp, then lift out the head carriage and remove the 


Dismantling the disk-inserted levers

(These are the linkages on the left-hand disk guide.)

Unhook the torsion spring and slide out the eject interlock flap. Remove 
the spring

Unhook the torsion spring on the latch lever (top rear of the guide). 
Remove the E-circlip, the torsion spring and the latch lever

Unhook the torsion spring on the disk-present lever (under the front of 
the guide. Remove the E-circlip, the torsion spring and the disk-present 

Remove the E-circlips on the mounting posts for the frontpanel button 
slide. Remove the 2 washers, lift off the slide and recover the following 
parts : 2 spacers and 2 washers from the mounting posts ; 2 rollers from 
the slide ; 1 reaction plate from the guide


Dismantling the disk clamp assembly

Pull the disk clamp lever away from the bridge by hand until the disk 
clamp cone is free of the spindle. Slide the clamp cone out of the end of 
the lever. 

Unhook the torsion spring. Remove the E-circlip from the end of the pivot 
spindle, slide out the spindle and remove the torsion spring. Separate 
the clamp lever from the bridge.

Unclip the 2 halves of the disk clamp cone and remove the compression 
spring. Press out the bearing. Remove the circlip and slide the bush out 
of the centre of the bearing.


Clamp Bearing
ID : 4.6mm
OD : 9.5mm
Thickness 3.17mm (1/8")

Motor Bearings and Belt Idler
ID : 3mm
OD : 8mm
Thickness : 4mm

Spindle Bearings
ID : 4.75mm
OD : 9.5mm
Flange OD : 10.8mm
Total Thickness : 3.15mm
Flange Thickness : 0.75mm


SD320 links : 

SS1 (6 position DIP switch)
1 : Drive select 0
2 : Drive select 1
3 : Drive select 2
4 : Drive select 3
5 : Head load from pin 4 of interface connector   *
6 : Head load from drive select 

SS2 : 
HS : Load controlled by head-load signal   *
MS : load controlled by motor enable 

SS3 : 
DS : In-use LED controlled by drive select
HL : In-use LED controlled by head load drive  *


Testpoints : 
1 : Ground

2 ) Differential outputs of read amplifier
3 )

4 ) Differential inputs to comparator
5 )

6 Index sensor 

7 Index pulse

8 Drive Select/

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