the Mountain Computer Expansion Box
   a legendary expansion to the Apple ][ series
  reverse engineered and de-mystified

    Page No.:H054-4
 
     
      Copyright note: The pictures used in this page, have been taken from members gsmcten, macnoyd* and Keatah ( all members at the Applefritter Forum )
                              * the pictures from macnoyd, result from the ebay offer he successfully won
                                 Therefor the copyrights of the pictures displayed at this page remain of course to the members at AF whom the units belong.
                                 The other pictures here resulting from the reengineering process remain with their copyright to me and none of the contents from this
                                 page may be used ( not even partially ) in any other webpage without the permission of the copyright owners.

 		  
     
 		  
   
    
  Well in this page i want to link the theory together with the "real world" by displaying pictures of details from the mainboard in conjunction
  with the function groups explained in the previous page. I will use the same notations and the same numberings to enable a comparing view
  of both parts besides eachother ( if printed and placed besides eachother ).

   Within the thread at AF there has been mentioned, that there are in general 2 versions of the box. The comparing of the differences will be performed
   also within this page.
 
   

 part 1 and 2 the oscillators within the powersupply

             
  this is the "standard" version in older boxes:   this is the "alternate" version in newer boxes:  
     
  part 3 and 4 the Power MOS FETs within the powersupply      
  this is the "standard" version in older boxes:   this is the "alternate" version in newer boxes:  
     
    part 5 the "switching coil" within the powersupply - itīs from plain view same in both versions:    
 
 the data from the switching coil
 will be explained later in a own
 page.  That page contains the
 data upon the material used for
 the coil itself as well as - based
 to measurements - the data to
 the amount of windings.

 The 2 primary windings at the
 bottom of this picture are kind
  of "centertapped" and the
  opposing ends are tied to the
  Power MOS FETs.
 
  The secondary side at the top
  of the picture consist of 4 in-
  dependant windings that end
  up at rectifying diodes and the
  voltage getīs smoothened by
  the added electrolytic capaci-
  tors. Those voltages with
  stronger current ( +5 Volt and
  +12 Volt ) then are filtered with
  coils that operate as "low pass"
  blocking away the high frequen-
  cy from the positive trace of the
  circuitary.





 
part 6 "the primary rectifing part" within the powersupply upfront of the regulating IC in part 7
 - itīs from plain view same in both versions:
      The "big caps" may be from different manufacturers - the
people at Mountain
Computer used capa-
citors from: Mallory
and other brands.
When replacing them
by repair the only
limitation will be to ensure that both "big caps" should be from very same kind and therefor they should allways be replaced as pair - even also if only one capacitor has been damaged.
When replacing of course the polarity must be correct - otherwise this capacitors will		       
    explode like bombs !    
part 7 "the first regulation of the voltage" within the powersupply upfront of the "switching powersupply"
 - itīs from plain view same in both versions:

The SG340K 24 is a fixed 24 Volt positive IC Voltage regulator for regulation of up to 1,5 Ampere.

If it must be replaced you must be sure that the replacement is able to
handle up to 50 Volt maximum inputvoltage  and it must be able to handle in normal operation at least
1,5 Ampere !
 
part 8 is the "apple II power up detection" unit within the powersupply
 - itīs from plain view same in both versions:

 the "Apple II powered up detection" makes
 sure, that the Mountain Computer Expansion
 Box can only be used while the Apple II is
 powered up - this parts here detect, if at the
 Apple II the power is switched on by
 detecting at the +12 Volt - if power is present
 - if not this parts make sure that the
 oscilators ( part 1 and part 2 ) donīt start
 swinging and therefor then the parts behind
 the powersupply of the box ( behind the
 "switching coil" remain without power.

 
part 9 is partialy the "apple II power up detection" unit and the other part of the IC is responsible for the frontpanel
 - itīs from plain view same in both versions:
   
  As explained in the picture right sided - the common
  connection of resistor R17 and R18 lead to pin 6 at U8.

  Pin 3 of U1 ( the NE555 ) leads to pin 6 of the frontpanel-
  plug and then within the yellow cable to the top of the
  "in Use"-LED.

  Pin 4 of U1 ( the NE555 ) leads up to pin 2 of U11.

  The left side of the resistor R14 gets information from
  pin 2 of the Frontpanel-plug and the red cable from the
  center of the "select / deselect switch" and leads up to
  pin 9 of U7.

  And finally the left side of the resistor R13 gets info
  from pin 1 of the frontpanelplug that has connection
  by the brown cable to the "select / deselect switch"
  and then leads up to the pin 13 of U7.

  This four lines together mentioned in the previous page
  as the "special-lines" or claimed at AF to be the "Riddle"
  interact together with the line from the previous point of
  part 8 ( detecting the +12 Volt from the Apple II as "power
  up" signal ) as the complate Apple II detection circuit and
  the functionblock that is responsible to determine if the
  activity is to be performed by the Apple II or by the box -
  depending to the status of the "select / deselect" switch !

   The "trick" of selecting among the slots of the box and
   the slots of the Apple II is executed by the selection of
   "soft-switches" within the reserved adressing I/O range
   of the Apple II.		         
         
part 10 is the connector to the frontpanel
 - itīs from plain view same in both versions:
         
  The left picture displays the "front-
  panel plug" connector in the very
  right front of the mainboard.
 
  The picture at the left below displays
  the plug from the wiring at the front-
  panel inserted in that connector.

  the upper right picture displays the
  cables at the backside of the
  frontpanel and the wiring.

  The picture at the lower right side
  displays the frontview of the related
  part of the frontpanel of the box -
  with the 2 indication LEDīs above the
  "select / deselect" switch.		          
         
part 11 is part of the powersupply behind the "switching coil" and itīs responsible for the + 12 Volt
 - itīs from plain view same in both versions:

  The 2 outer pins of D5 ( C8212-004 ) are connected to the
  endings of one of the coils ( the 12 Volt one, consisting of
  the thicker wire ) within the "switching coil" unit ( part 5 )
  and then the rectified voltage is released at the centered
  pin of D5 leading to the positive pin of the electrolytic
  capacitor C8 that smoothens the voltage before it is
  passed over to the Coil L2 which shall filter the high-
  frequency noise away from the + 12 Volt branch and then
  the voltage is delivered to the rest of the box ( in general
  to the slots ) .
 
part 12 is part of the powersupply behind the "switching coil" and itīs responsible for the + 5 Volt
 - itīs from plain view same in both versions:

  The 2 outer pins of D4 ( C8212-004 ) are connected to the
  endings of one of the coils ( the 5 Volt one, consisting of
  the thicker wire ) within the "switching coil" unit ( part 5 )
  and then the rectified voltage is released at the centered
  pin of D4 leading to the positive pin of the electrolytic
  capacitor C7 that smoothens the voltage before it is
  passed over to the Coil L2 which shall filter the high-
  frequency noise away from the + 5 Volt branch and then
  the voltage is delivered to the rest of the box ( in general
  to the slots  and to the ICīs U1 till U11) .
 
part 13 is part of the powersupply behind the "switching coil" and itīs responsible for the - 5 Volt
 - itīs from plain view same in both versions:

  The 2  pins of D7 and D3  are connected to the
  endings of one of the coils ( the 5 Volt one, consisting of
  the thiner wire ) within the "switching coil" unit ( part 5 )
  and then the rectified voltage is released at the common 
  connected pins of D7 and D3  leading to the negative pin
  of the electrolytic capacitor C10 that smoothens the
  voltage before it is passed over to the resistor R20 which
  shall filter the high-frequency noise away from the - 5 Volt
  branch and then the voltage is delivered to the rest of the
  box ( in generalto the slots ) .
 
part 14 is part of the powersupply behind the "switching coil" and itīs responsible for the - 12 Volt
 - itīs from plain view same in both versions:

 
  The 2  pins of D6 and D2  are connected to the
  endings of one of the coils ( the 12 Volt one, consisting of
  the thiner wire ) within the "switching coil" unit ( part 5 )
  and then the rectified voltage is released at the common 
  connected pins of D6 and D2  leading to the negative pin
  of the electrolytic capacitor C9 that smoothens the
  voltage before it is passed over to the resistor R19 which
  shall filter the high-frequency noise away from the - 5 Volt
  branch and then the voltage is delivered to the rest of the
  box ( in generalto the slots ) .
 
 part 15 is the part of the "control line function block" within the "Apple part" of the box
 - itīs from plain view same in both versions:

   the control-line function block consists of the ICīs
   from U7 to U11.

   U11 ( 74LS04 ) can be viewed as a kind of "amplifier" -
   it only stregthens the signals that have been 
   "weakened" by the resistance ot the resistorpack at the
   IFcard and the length of the 50 pin flatribboncable up to
   powerfull signals again.

   The same is valid to U10 ( also 74LS04 ).

   The resistorpack RP7 operates as a network of "pullup-
   resistors" that interact with signals at U11 and U10.

    The ICīs U9 ( 74LS125 ) act like a collection of 4
     "pass through"-gates each also having own kind
     of "enable"-pin that permits to lock or unlock a gate.

    U8 ( 74LS02 ) and U7 ( 74LS08 ) perform the "logic-
    knitting" where some signals are linked together and
    act like a kind of "logical-switches" that permit the use
    of the box-slots or disables them. here is the logic of
    the "soft switches" integrated together with the inter-
    action with the "select / deselect" switch and the lines
    that lead to the indication of the "status of the box"
    at the frontpanel displaying if the the Apple II is "power
    up" and the box is "selected" or not.
part 16 is the part of the "data line function block" within the "Apple part" of the box
 - itīs from plain view same in both versions:

  U6 is a bus transciever ( 74LS245 ) - it can be compared
   to a valve with 2 functions: one function permits the
   water to flow or to be shut ( this is performed by the
   pin 19 - CE = Chip Enable ) if that pin gets 5 Volt it 
   permits the flow of the data and if at pin 19 is 0 Volt
   present the chip "shuts communication" and behave
   to be "invisible" in both directions.

   the second part of the control may be compared to 
   valves, that permit either the warm water or the cold
   water to flow. At the IC this is performed by the pin 1
   which is at the IC called DIR and that controls the
   direction in which communication may flow
    - it determins if the information is from slot of the box
    to Apple II or from Apple II to the slots of the box.

    The chip controls 8 lines ( D0 to D7 ) which represent
    the entire databus.
part 17 is the part of the "adressing line function block" within the "Apple part" of the box
 - itīs from plain view same in both versions:

  U5 and U4 are bus transcievers ( 74LS245 ) - they can be
   compared to a valve with 2 functions: one function
   permits the water to flow or to be shut ( this is performed
   by the pin 19 - CE = Chip Enable ) if that pin gets 5 Volt it 
   permits the flow of the data and if at pin 19 is 0 Volt
   present the chip "shuts communication" and behave
   to be "invisible" in both directions.

   The second part of the control may be compared to 
   valves, that permit either the warm water or the cold
   water to flow. At the IC this is performed by the pin 1
   which is at the IC called DIR and that controls the
   direction in which communication may flow
    - it determins if the information is from slot of the box
    to Apple II or from Apple II to the slots of the box.

    U5 and U4 control the entire adressing bus.

    The chip U4 controls 8 lines ( A0 to A7 ) which represent
    the lower half of the adressingbus.   
    The chip U5 controls 8 lines ( A8 to A15 ) which represent
    the upper half of the adressingbus.
part 18 is the part of the "device select function block" within the "Apple part" of the box
 - itīs from plain view same in both versions:

  The device select function block operates by delivering
  the DEVSEL to one slot at a time - that is performed by a
  demuxer chip - in this case a 74LS138 that recives 3
  adressinglines at the one input pin group and the other
  group of input disables or enables the chip from decoding
  the adressing lines if the correct settings are given. Then -
  if decoding is enabled one of the 8 output lines of the
  chips is set to low. This part is performed by the IC U3.
part 19 is the part of the "I/O selection function block" within the "Apple part" of the box
 - itīs from plain view same in both versions:
  The device select function block operates by delivering
  the I/O SEL to one slot at a time - that is performed by a
  demuxer chip - in this case a 74LS138 that recives 3
  adressinglines at the one input pin group and the other
  group of input disables or enables the chip from
  decoding the adressing lines if the correct settings are
  given. Then - if decoding is enabled one of the 8 output
  lines of thechips is set to low. This part is performed by
  the IC U2.
part 20 is the part of the "Apple slots block" within the "Apple part" of the box
 - itīs from plain view same in both versions:

   The block of the 8 Apple slots are absolutely a copy of
   the slots in the Apple II, with the exact same decoding
   and absolut same signals as at the Apple II. The only
   difference is given by the fact that by a switch of the box
   the user may decide if the slot is enebled at the Apple II by
   deselecting the box or disabled by selecting the box.

   But none of the slots within the box is usable unless
   the Apple II is connected correct and powered up.

   The electrolytic capacitors located between the slots just
   buffer the voltages at the slots to avoid any kind of
   dropout resulting from heavy loads.

 

  
     
    
         
         
       
     
   
   here is the link to the next page - where the story is continued =>
 		  
 
 <= here is the link back to the previous page

  		 
 
 <= here is the links to turn back to the indexpage of the Applebox
 		  
     
 
         
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 I hereby declare no responsibility to any "deep links" resulting from the links in this page. I have no influence to the pages linked hereby in this page and the
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