
W R E N   I I H H   9 4 2 0 5 - 5 1    CDC
NO MORE PRODUCED                                      Native|  Translation
                                                      ------+-----+-----+-----
Form                 5.25"/HH              Cylinders     989|     |     |
Capacity form/unform    43/   52 MB        Heads           5|     |     |
Seek time   / track  28.0/ 5.0 ms          Sector/track   17|     |     |
Controller           MFM / ST506           Precompensation   128
Cache/Buffer               KB              Landing Zone
Data transfer rate    0.625 MB/S int       Bytes/Sector      512
                      0.625 MB/S ext
Recording method     MFM                            operating  | non-operating
                                                  -------------+--------------
Supply voltage     5/12 V       Temperature *C        10 50    |    -40 70
Power: sleep              W     Humidity     %         8 80    |      5 95
       standby            W     Altitude    km    -0.305  3.048| -0.305 12.210
       idle          18.0 W     Shock        g         2       |     32
       seek          20.0 W     Rotation   RPM      3597
       read/write         W     Acoustic   dBA
       spin-up            W     ECC        Bit
                                MTBF         h      40000
                                Warranty Month
Lift/Lock/Park     YES          Certificates     CSA,FCC,IEC380,UL478,VDE


**********************************************************************
                        L   A   Y   O   U   T
**********************************************************************
SEAGATE  ST253  PRODUCT MANUAL 77738213-E

  +------------------------------------------------------+
  |                                                      |XX Power
  |                                                      |XX
  |                                                      |
  |                                        Terminator++  |X1 Control
  |                                        Resistor  ||  |XX Cable
  |                                                  ||  |XX Connector
  |                                                  +1  |XX
  |                                                      |XX
  |                                          Drive   +-+ |XX
  |                                          Select  | | |XX
  |                                          Jumper  | | |
  |                                                  +-+ |X1 Data
  |                                                      |XX Cable
  |                                                      |XX Connector
  |                                                      |XX
  |                                                      |XX
  +------------------------------------------------------+



**********************************************************************
                      J   U   M   P   E   R   S
**********************************************************************
SEAGATE  ST253  PRODUCT MANUAL 77738213-E

 Jumper setting
 ==============

 Drive Select Jumper
 -------------------

      +------------+--------------------+
      |            | 1  2  3  4  5  6  7|
      +------------+--------------------+
      |Drive 1     | X  o  o  o  o  o  o|
      |            | X  o  o  o  o  o  o|
      +------------+--------------------+
      |Drive 2     | o  X  o  o  o  o  o|
      |            | o  X  o  o  o  o  o|
      +------------+--------------------+
      |Drive 3     | o  o  X  o  o  o  o|
      |            | o  o  X  o  o  o  o|
      +------------+--------------------+
      |Drive 4     | o  o  o  X  o  o  o|
      |            | o  o  o  X  o  o  o|
      +------------+--------------------+
      |Radial      | o  o  o  o  X  o  o|
      |            | o  o  o  o  X  o  o|
      +------------+--------------------+
      |Reserved    | o  o  o  o  o  X  o|
      |            | o  o  o  o  o  X  o|
      +------------+--------------------+
      |Reserved    | o  o  o  o  o  o  X|
      |            | o  o  o  o  o  o  X|
      +------------+--------------------+




 WREN Interface Control Cable
 ----------------------------
                  Signal Direction    Signal Direction
   +-----------+                                      +-------------+
   |           |                                      |Signal Ground|
   |           | Terminated                           |No.    No.   |
   |           +------------------------------------->|  2     1    |
   |           | Head Select 2(2)                     |             |
   |           +------------------------------------->|  4     3    |
   |           | Write Gate                           |             |
   |           +------------------------------------->|  6     5    |
   |           | Seek Complete                        |             |
   |           |<-------------------------------------+  8     7    |
   |Controller/| Track 0                              |             |
   |Host       |<-------------------------------------+ 10     9    |
   |Interface  | Write Fault                          |             |
   |           |<-------------------------------------+ 12    11    |
   |           | Head Select 2(0)                     |             |
   |           +------------------------------------->| 14    13    |
   |           | Reserved  to J3 pin 7                |             |
   |           +--------------------------------------+ 16    15    |
   |           | Head Select 2(1)                     |             |
   |           +------------------------------------->| 18    17    |
   |           | Index                                |             |
   |           |<-------------------------------------+ 20    19    |
   |           | Ready                                |             |
   |           |<-------------------------------------+ 22    21    |
   |           | Step                                 |             |
   |           +------------------------------------->| 24    23    |
   |           | Drive Select 1                       |             |
   |           +------------------------------------->| 26    25    |
   |           | Drive Select 2                       |             |
   |           +------------------------------------->| 28    27    |
   |           | Drive Select 3                       |             |
   |           +------------------------------------->| 30    29    |
   |           | Drive Select 4                       |             |
   |           +------------------------------------->| 32    31    |
   |           | Direction In                         |             |
   |           +------------------------------------->| 34    33    |
   |           |                                      |             |
   +-----------+                                      +-------------+
                                                       WREN Control
                                                       Cable Connector

   All signals in the control cable are single ended signals.

 Pin 2 in the control cable (Head Select 2(3) is defined as Reduced
 Write Current in the Seagate ST412 interface. The WREN II HH controls
 write current internally, and thus the line is not needed for this
 function and is terminated.


 DC 506 Interface Data Cable
 ---------------------------
                  Signal Direction    Signal Direction
   +-----------+                                      +-------------+
   |           |                                      |Pin No. Type*|
   |           | Drive Selected                       |             |
   |           |<-------------------------------------+  1      SE  |
   |           | Ground                               |             |
   |           +--------------------------------------+  2          |
   |           | Reserved                             |             |
   |           +--------------------------------------+  3      SE  |
   |           | Ground                               |             |
   |           +--------------------------------------+  4          |
   |Controller/| Motor On (Option)                    |             |
   |Host       +--------------------------------------+  5      SE  |
   |Interface  | Ground                               |             |
   |           +--------------------------------------+  6          |
   |           | Reserved  to J4 Pin 16               |             |
   |           +--------------------------------------+  7          |
   |           | Ground                               |             |
   |           +--------------------------------------+  8          |
   |           | Reserved                             |             |
   |           +--------------------------------------+  9          |
   |           | Reserved                             |             |
   |           +--------------------------------------+ 10          |
   |           | Ground                               |             |
   |           +--------------------------------------+ 11          |
   |           | Ground                               |             |
   |           +--------------------------------------+ 12          |
   |           | +MFM Write Data                      |             |
   |           +------------------------------------->| 13      DIFF|
   |           | -MFM Write Data                      |             |
   |           +------------------------------------->| 14      DIFF|
   |           | Ground                               |             |
   |           +--------------------------------------+ 15          |
   |           | Ground                               |             |
   |           +--------------------------------------+ 16          |
   |           | +MFM Read Data                       |             |
   |           |<-------------------------------------+ 17      DIFF|
   |           | -MFM Read Data                       |             |
   |           |<-------------------------------------+ 18      DIFF|
   |           | Ground                               |             |
   |           +--------------------------------------+ 19          |
   |           | Ground                               |             |
   |           +--------------------------------------+ 20          |
   |           |                                      |             |
   +-----------+                                      +-------------+
                                                       Data Cable
                                                       Connector

 * SE   = Single Ended Signal
   DIFF = Differential Signal


 Drive Select 1-2-3-4
 --------------------
 These lines are used to activate a device's drivers and receivers for
 up to four drives in a daisychained operation. The following
 characteristics apply to the DRIVE SELECT lines:

  1.   Logical unit designation is accomplished at the time of
       installation by setting the jumper plug located on the
       baseboard assembly.

  2.   All command cable lines are gated with Drive Select. No data
       cable signal lines are gated with Drive Select.

  3.   Drive Select must remain active during any communication with
       the host controller.

  4.   When the radial select jumper is installed, the drive will be
       selected all the time.

  5.   The drive should not be selected until 1 second after DC power
       is applied. The Ready input will be valid within 500 ns
       after the drive is selected (Drive Selected true) and after the
       power on delay.

  6.   The drive will be selected within 1  s after the activation of
       Drive Select, if the power on sequence is complete. The drive
       will be the deselected within 1  s after the deactivation of
       Drive Select.

  7.   The drive will activate the Drive Selected signal within 1  s
       after receipt of Drive Select if the drive is selected. The
       drive will deactivate Drive Selected within 1  s after the
       Drive Select signal is deactivated.

  8.   Drive Select must be valid 100 ns minimum before the first step
       pulse is received and 100 ns minimum after the last step pulse
       is received.

  9.   At the completion of a write operation, Drive select must
       remain active for 1  s.

 10.   When the Drive Select line is activated, a head change will
       occur, thus requiring a delay of 5  s before a read or write
       operation can be initiated.




 DC Power and pin connector assignments
 --------------------------------------
      +------------+   pin 1    +12 VDC
      | 1  2  3  4 |   pin 2    +12 Volts Return
      +------------+   pin 3    + 5 Volts Return
                       pin 4    + 5 VDC



**********************************************************************
                      I   N   S   T   A   L   L
**********************************************************************
SEAGATE  ST253  PRODUCT MANUAL 77738213-E

 Notes on installation
 =====================

 Drive mounting
 --------------

     horizontally             vertically
   +-----------------+   +--+             +--+ +------------------+
   |                 |   |  +-----+ +-----+  | |                  | x
   |                 |   |  |     | |     |  | x+----------------+x
 +-+-----------------+-+ |  |     | |     |  | ||x              x||
 +---------------------+ |  |     | |     |  | ||  x          x  ||
                         |  |     | |     |  | ||    x      x    ||
      x           x      |  |     | |     |  | ||      x  x      ||
 +------x------x-------+ |  +-----+ +-----+  | ||       xx       ||
 +-+------x--x-------+-+ +--+             +--+ ||     x    x     ||
   |       xx        |                         ||   x        x   ||
   |     x    x      |                         || x            x ||
   +---x--------x----+                         |x                x|
     x            x                           x++----------------++x
      UNACCEPTABLE!                                UNACCEPTABLE!





 Drive Orientation
 -----------------
 The permissible drive mounting orientations include operation in the
 horizonatal plane and in the vertical plane. Mounting with either end
 down (front or rear) is not permissible. An angle of (TBD) is
 acceptable for both horizontal and vertical orientations.

 WREN II HH is designed, manufactured, and tested with a "Plug-in and
 Play" installation philosophy. This minimizes the requirements for
 highly trained personnel to integrate the WREN II HH into an OEM's
 system, wether in a factory or field environment.


 Cooling
 -------
 Cabinet cooling must be designed by the customer so that the ambient
 temperature immediately surrounding the WREN II HH will not exceed
 temperature conditions.

 Interface Cabling Options
 -------------------------

 View A
    +---------------------Host-Controller---------------------+
    |                                                         |
    |Data Command   Data Command  Data Command   Data Command |
    +--+-----+--------+-----+--------+-----+--------+-----+---+
       |     |        |     |        |     |        |     |
       |     |        |     |        |     |        |     |
       |     |        |     |        |     |        |     |
       |     |        |     |        |     |        |     |
    +-++-+--++-+-+ +-++-+--++-+-+ +-++-+--++-+-+ +-++-+--++-+-+
    | |R |  | T| | | |R |  | T| | | |R |  | T| | | |R |  | T| |
    | +--+  +--+ | | +--+  +--+ | | +--+  +--+ | | +--+  +--+ |
    |    WREN    | |   WREN     | |   WREN     | |   WREN     |
    +------------+ +------------+ +------------+ +------------+

    Each command cable length must not exceed 20 feet (6.10m). Each
    data cable length must not exceed 20 feet (6.10m).


   T  indicates terminator resistor pack.
   R  indicates discrete terminator.
   WREN data cables are permanently terminated.


 Radial Configuration
 --------------------
 View A shows each drive interfaced to its own command cable, which
 allows interfacing of any number of drives and a variety of
 system operational techniques. Each drive has its data cable and
 command cable radially connected to the host controller. The length
 of each individual cable must not exceed 20 feet (6.10 meters).
 Terminator resistors must be installed in the host controller for
 each data cable and for each command cable.




 View B
    +---------------------Host-Controller---------------------+
    |                                                         |
    |Data Command   Data          Data           Data         |
    +-+------+-------+--------------+--------------+----------+
      |      |       |              |              |
      |      |       |              |              |
      |      |       |              |              |
      |      +-------+Command+------+Command+------+Command+
    +++-+----+---+ +++-+-----+--+ +++-+-----+--+ +++-+----++-++
    ||R |        | ||R |        | ||R |        | ||R |    | T||
    |+--+        | |+--+        | |+--+        | |+--+    +--+|
    |    WREN    | |    WREN    | |    WREN    | |    WREN    |
    +------------+ +------------+ +------------+ +------------+

    Total command cable length must not exceed 20 feet (6.10m). Each
    data cable length must not exceed 20 feet (6.10m).


   T  indicates terminator resistor pack.
   R  indicates discrete terminator.
   WREN data cables are permanently terminated.


 Daisychain Configuration
 ------------------------
 A daisychain configuration incorporates a parallel interfacing on the
 disc drives on a common command cable.  A maximum of four drives may
 be daisychained on the command cable. Only the drive which is
 selected by the host system has its control and data signals enabled
 through this common interface. View B consists of four WREN II HH
 Disc Drives only. Only the last WREN II HH in the daisychain requires
 a terminator resistor pack for the command cable. Terminator resistor
 packs for the command cable or other drives are removed. The total
 combined command cable length (from the controller to the first
 drive, to the second and subsequent drives) must not be more than 20
 feet (6.1 meters).


 DC Cable and connector
 ----------------------
 The WREN II HH receives DC power through a 4 pin right angle
 connector mounted on the main circuit board. Recommended part number
 for the mating connector are included below, but equivalent parts may
 be used.

 Type of cable:      18 AWG
 Connector:          AMP 1-480424-0
 Contacts:           AMP 60619-4 (Loose Piece); AMP 61117-4 (Strip)


 Device Grounding
 ----------------
 The WREN II HH is shipped with the DC Logic ground and the chassis
 ground joined together. These two ground planes may be separated by
 repositioning the motor control board ground washer.

 Note: If the grounds are to be separated, the washer must be oriented
 so that it does NOT contact the ground run near the screw AT ANY
 POINT.


 Data Cable and Connector
 ------------------------
 The I/O connector for the data interface is a 20 pin board edge
 connector. The odd pins are located on the front side of the
 printed circuit board. The even pins are on the back side of the
 printed circuit board. A key slot is provided between pins 3 and 5.
 CDC recommends keying this connector to prevent the possibility of
 installing it upside down.

 Recommended part numbers for the mating connector are included below,
 but equivalent parts may be used.

 Connector:          20 pin, 3M-3461-0001, AMP 88373-6 or AMP 111109-3
 Cable:              Flat Cable (Stranded AWG 28) 3M-3365-20
                     Flat Cable (Stranded AWG 28) 3M-3517-20 (Shielded
                     Cable)
 Key:                AMP 583274-1, 3M-3439-0000


 Command Cable and Connector
 ---------------------------
 The I/O connector for the command interface is a 34 pin board edge
 connector. The odd pins are located on the front side of the
 printed circuit board and are connected to the ground plane. The even
 pins are on the back side of the printed circuit board. A key
 slot is provided between pin 3 and 5. CDC recommends keying this
 connector to prevent the possibility of installing it upside down.

 Recommended part numbers for the mating connector are included below,
 but equivalent parts may be used.

 Connector:          34 pin, 3M-3463-0001, AMP 88373-3 or AMP 111109-3
 Key:                AMP 583274-1, 3M-3439-0000
 Cable:              Flat cable (Stranded AWG 28) 3M-3365-34
                     Flat cable (Stranded AWG 28) 3M-3517-34 (Shielded
                     Cable)
                     Spectra Strip Twist'n Flat 455-248-34 (Stranded
                     AWG 28 Twisted Pair)


 Interface Drivers/Receivers
 ---------------------------
 The WREN II HH uses both single ended and balanced differential
 signals on the I/O. The data signals use balanced differential
 drivers and receivers. All other signals use single ended drivers and
 receivers.

 Single Ended Drivers/Receivers
 -------------------------------
 Transmitter Characteristics
 The WREN II HH uses the 74F38 open collector quad-2-input driver to
 transmit status to the host. This driver is capable of sinking a
 current of 48 mA with a low-level output voltage of 0.4V.

 Receiver Characteristics
 The WREN II HH uses the 74LS14 Hex Inverter with hysteresis gate as a
 line receiver. The input of each receiver is terminated in a 220/330
 ohm resistor network.

 Terminator Characteristics
 The terminator consists of a resistor module which plugs into a
 socket in the last drive in a daisychain. Each drive is furnished
 with a terminator. Terminators must be removed from all except the
 last drive on the cable prior to daisychain operation. The terminator
 can be easily removed with tweezers or needlenose pliers. Terminator
 installation will, however, require some disassembly of the drive.
 An equivalent terminator must be provided in the controller on each
 input signal line from the drive to the controller. Only the Command
 cable resistor module is removable.


 Balanced Differential Drivers/Receivers
 ---------------------------------------
 Transmitter Characteristics
 The WREN II HH uses 75158 type balanced differential driver. Logic 1
 on the interface is defined when the "+" output is more positive than
 the "-" output.

 Receiver Characteristics
 ------------------------
 The WREN II HH uses 75157 type balanced differential receivers.
 Logic 1 on the interface is defined when the "+" input is more
 positive than the "-" input.

 Terminator Requirements
 -----------------------
 Each differential receiver in the drive is terminated with a 100 ohm
 resistor. An equivalent terminator must be provided in the controller
 on each input signal line from the drive to the controller.


 Digital Interface Signal Definitions
 ------------------------------------
 The WREN II HH uses the two cable (command and data) interface for
 information transfer between it and the controller/host system.
 (All single ended signals are true when the interface voltage level
 is less than 0.4 volts.)


 Remote Motor Start Option
 -------------------------
 The WREN II HH will support remote start control capability via a
 user specified option. This option utilizes a reserved line on the
 data cable (pin number 5) to enable the motor ON routine in the
 drive. If this option is not selected, Pin 05 will be open and non-
 functional. If this option is installed, Pin 05 will start the
 spindle concurrent with a high level.



**********************************************************************
                      F   E   A   T   U   R   E  S
**********************************************************************
SEAGATE  ST253  PRODUCT MANUAL 77738213-E

 Standards
 ---------
 The 94205-XX WREN II HH has been developed as a system
 peripherals to the highest standards of design and construction. The
 WREN depends upon its host equipment to provide adequate power and
 environment in order to achieve optimum performance and compliance
 with applicable industry and governmental regualations. Special
 attention must be given in the areas of safety, power distribution,
 shielding, audible noise control, and temperature regulation.

 The WREN II HH is a UL Recognized component per UL478 and a CSA
 Certified product per CSA C22.2, No. 154-M1983. It also meets the
 requirements of DIN IEC 380/VDE 0806/8.81.

 The WREN II HH, as delivered, is designed for system integration
 before use. It is supplied as a Class A Computing Device per the FCC
 Rules and Regulations, Part 15, Subpart J governing EMI of computing
 devices. However, the WREN II HH has been tested and found to comply
 with the Class B requirements of the referenced FCC Rules and
 Regulations when installed in a typical commercial computing system.

 The head, disc and actuator chamber (HDA) is environmentally sealed
 at the factory. Air is recirculated within the HDA and passes through
 a nonreplaceable filter to ensure the maintenance a contamination
 free disc/actuator environment.

 The WREN II HH uses a dedicated landing zone at the innermost
 radius of the media thus eliminating the possibility of destroying or
 degrading data by landing in the data zone.

 The WREN II HH incorporates an automatic shipping look which
 prevents potential damage to the heads and disks caused by movements
 during shipping and handling. The shipping lock is automatically
 disengaged when power is applied to the drive.

 The WREN II HH decodes Track 0 location from the dedicated servo
 surface thereby eliminating mechanical transducer adjustments and
 related reliability concerns.

 The WREN II HH uses a high performance actuator assembly
 consisting of a low inertia, balanced, straight arm driven by a
 by a highly efficient pancake coil assembly. This actuator mechanism
 (patent pending) provides excellent performance with minimal power
 dissipation.


 Media Description
 -----------------
 The media used on the WREN  has a diameter of approximately 5
 inches (130 mm). The aluminum substrate is coated with lubricated
 ferrous oxide which permit the heads to contact the surface when
 starting and stopping.

 Each data surface has total of 989 tracks and is capable of record-
 ing 10,301,424 bytes of unformatted data.

 Media defects are characterized as beeing either correctable or
 uncorrectable as a function of the type and magnitude of the media
 flaw. Various error correction codes may be implemented to correct
 errors in the data read from the disk. However, the code chosen
 should be consistent with Control Data media testing and
 certification methods. In the WREN II HH media certification is
 performed using the following standards:

            An error burst of 11 bits or less is a correctable error.

            An error burst greater than 11 bits in length is an un-
            correctable error.

 Host systems using the WREN II HH should have, as a minimum, resident
 capabilities to recognize and map defective tracks and perform track
 reallocation routines.

 At the time of shipment from the point of manufacture, the WREN II HH
 recording surfaces will meet the following requirements.

       1. 989 total tracks per surface.

       2. Track 0 to be error free on each data surface.

       3. 15 defects per surface maximum.

       4. Accumulative defects not to exceed 1 per megabyte, based on
          total available unformatted drive capacity.


 Driver/Receiver Characteristics
 -------------------------------
 Logic Level                   Drive Output         Receiver Input
 --------------------------------------------------------------------
 High (false/deactivated) (0)     2.5 V;   5.25 V      2.0 V;   5.25 V
 Low (true/activated)     (1)     0.4 V;   0.0 V       0.5 V;   0.0 V

 The difference in the voltages between input and output signals is
 due to the losses in the cable.


 Seek Time
 ---------

                                          | WREN II|
        ----------------------------------+--------+
        Track-to-Track         msec. typ. |   5    |
                               msec. max. |   8    |
                       Average msec. typ. |  28    |
                       Average msec. max. |  32    |
        Maximum Seek Time      msec. typ. |  65    |
                               msec. max. |  70    |
        Latency                msec. avg. |   8.34 |
        ----------------------------------+--------+

 Seek time is defined as the elapsed time from the receipt of a seek
 command by the WREN II HH until the drive signals the controller that
 it is ready to perform another seek, or a read/write function on the
 new cylinder. Average seek time is determined by dividing the sum of
 the time for all possible movements by the total number of movements.


 Start/Stop Time
 ---------------
 The WREN II HH will become ready less than 35 seconds after
 application of DC power. Stop time will be less than 30 seconds after
 removal of DC power.

 There is no power control switch on the drive.

 Spindle Speed and Latency
 -------------------------
 The spindle speed is 3597   0.5% r/min. The speed tolerance includes
 motor performance and motor control circuit tolerances.

 The average latency time is 8.34 milliseconds, based on a nominal
 disc speed of 3597 r/min. The maximum latency time is 16.76 milli-
 seconds based on a maximum disc speed of 3579 r/min.


 Read Data Transfer Rate
 -----------------------
 The nominal read serial data transfer rate is 5.0 Mbits per second.


 Air Cleanliness
 ---------------
 The WREN II HH is designed to operate in a typical office environment
 with minimum environmental control.



 Power Sequencing
 ----------------
 Power sequencing is not required for the WREN II HH. It protects
 against inadvertent writing during power up and down. Daisychain
 operation requires that power be maintained on the terminated unit to
 ensure proper termination of the peripherals I/O.


 Heat/Power Dissipation
 ----------------------
 Each WREN II HH will typically dissipate 20 watts (68 BTU per hour)
 of power during operation (seeking). Idle mode power dissipation is
 less than 18 watts, typically.


 Temperature
 -----------
 50*F to 122*F (10*C to 50*C) operating ambient with a maximum
 gradient of 18* F (10* C) per hour. Above 1000 feet (305 metres)
 altidude the maximum temperature is derated linearly to 112* F
 (44*C) at 10,000 feet (3048 metres). Cabinet packaging designs must
 provide ample air circulation around the WREN II HH to make sure
 environmental limits are not exceeded as a result of heat transfer
 from other system components. Operating ambient for specification
 purposes is defined as the environment immediately surrounding the
 WREN II HH. The temparature of the HDA is restricted to a maximum of
 143*F (62*C) during operation.

 Write Precompensation
 ---------------------
 MFM Write Data must conform to the conventional MFM encoding rules
 and must be write precompensation by  12 ns per the industry standard
 MFM data write precompensation rules. Write precompensation is
 recommended on all tracks; however, write precompensation must be
 performed on tracks greater than Track 128.


 Reliability
 -----------
 The following reliability specifications assume correct host/drive
 operational interface has been implemented, including all interface
 timings, power supply voltages, environmental conditions, and
 appropriate data handling circuits in the host system.

 MTBF                     40,000 hours
 Service Life             5 years
 Preventive Maintenance   None required


