The Duodisk is added to this chapter related to the fact that this unit was introduced during the period of the Apple II+ to the market and the Duodisk was intended to be the regular sold set of 2 DiskII systems with the computer. In that days the storage capacity still was limited by the fact that 1 Floppydisk only contained 140 kByte of Data and 1 Disk contained the operation system ( at the right side as Drive 1 ) and maybe a program and the second disk ( as Drive 2 at the left side ) was intended to be used for storage of the data ( bearing in mind that a long period of time only diskdrives offered singleside mechanic ).

Other factors in that days have been limited by the fast that important components for the mechanic in that days have been limited too: The head positioning mechanic was too expensive and at the time of introduction the stepping motors got miniaturized and first stepping motors offered construction of so called "halfheight" drives saving space and reducing the track problems still caused by the mechanical positioning of the read/write head and its mechanical wearout.

This page  is focused on the service and splits  in two sections:
first section displays details about mounting / dismounting the drive and cables as well as locating the electronic components
and second sections displays the circuitplan and electronic details comparing the duodisk with the DISK II. The similarities demands to also read the previous pages of the DISK II because from view of the service still a lot of procedures still remain similar to the former drives.

It contains two single drives inside, each in a kind of Faraday-cage - which i call in the further part of the text a "RFI-protection-cage"  ( acting as shielding ).

The internal drives are locked each by 4 screws to the bottomshell.

Pay attention to the 2 small holes in the bottom shell each for access to the trimmer of the
internal drive tht controls the speed of the drive.  In that case a very small screwdriver is a important demand and the  screwdriver should look a bit like one of the ones displayed here:

TIP: to avoid electronic shortcut between PCB and grounded RFI protection cage the major part of the metal of the screwdriver should be covered except a tiny tip of the screwdriver blade with isolating shrink hose.

The 2 screws at the rear of the topshell fixe it at the bottomshell where that topshell is in place by support of the groove in the bottomshell.

Important info: the connector at the rear for the attachment of the cable from the Computer is NOT locked by any screws to the topshell. It is only locked in its place by screws to the internal cage of the internal drive!

At the bottom each internal driveframe and its bottom

cage is attached in its position at the bottom part of the caseshell with four screws to the bottom part of the

outer case.

Each bottom part of the two RFI protection cages is attached at the alternating sides by two screws to the frame of the internal drive mechanic. 

Before attaching the top part of the RFI-ptotection cage pay attention to the protection sleves at the cables that shall protect the cable wires against contact / shortcuts with the grounded shield cage and lead then to the outer electronic PCB on top above the drive 2.

Then the top part of the RFI protection cage is mounted to the bottom part by slipping into the two clamps at the bottom part of the RFI protection cage.

Both RFI-cage parts must have good and firm electronic contact with the grounding cable at the rear of the drives which is attached with screws and lead the grounding rail to the shielding of the cable connector at the rear of the duodrive.

While in the old system a Disk with grove and gliding
steel-ball ( see page 3 ) was used for movement here now is a steel-band fixed to the read/writehead to perform direct movement.

Except the location of the trimmer related to the speed adjustment the procedure of the speed adjustment itself is same like explained at page 2 for the DISK II !

the Block-shema

The major part of the the electronic at the Duodisk is similar to the DISK II - the remarkable difference results to the fact that a set of electronic switches has been added: That switches ensure that the signals from the Drivecable at the rear splits apart in 2 sections and detects to which internal drive the signals shall be sent - either Drive 1 - or Drive 2 - but never both drives  at the same time.

a second switch just splits between the function at the MC3470 - either read or write mode.

At the moment the first switch has not been completely analyzed. This will be added to this page in a later stage in several weeks in detail. At the moment its for service in general important to publish that parts, that are similar to the DISK II  and the minor differences to that drive.

The color markings and the capitals used in this block shema are same color and capitals I used in the following circuitplan and PCB-pictures.

At  part A the circuit is allocated to the CA3146 and the writecoil within the Read/Write head responsible for writing data to disk.

At part B of the plan the MC3470 is responsible for the amplification and "fashioning" of the signals from the read-coil reading data from disk.

Part C is buffering and cleaning the supplyvoltage and shall block spikes of away from the electronics.

Part D and E are sections for switching between read and write mode and indicating activity at the drive.

Part F related to the ULN2003 is responsible for buffering the handshakesignals between controller and the drives. Similar is valid to the 74LS125.

The remaining 6 chips that have been left without colormarking belong to the switching between Drive 1 and Drive 2.

At  part A the circuit is allocated to the CA3146 and the writecoil within the Read/Write head responsible for writing data to disk.

At part B of the plan the MC3470 is responsible for the amplification and "fashioning" of the signals from the read-coil reading data from disk.

Part C is buffering and cleaning the supplyvoltage and shall block spikes of away from the electronics.

Part D and E are sections for switching between read and write mode and indicating activity at the drive.

Part F related to the ULN2003 is responsible for buffering the handshakesignals between controller and the drives. Similar is valid to the 74LS125.

The remaining 6 chips that have been left without colormarking belong to the switching between Drive 1 and Drive 2.

Beware of the orientation of the missing pins at the plugs of the Read/Writeheads at the connectors to Drive 1 and Drive 2 !