=*=*=›      ATARI 1050 DISK DRIVE REPAIR›      Defective Head Park Switches›                  By D. R. HAULSEE›      Reprinted  from M.A.G.I.C.'s›      Newsletter  by  OL' HACKERS,›      with thanks!›› (I downloaded this article from one of› the  bulletin  boards that I visit.  I› can't remember which  one  or  when  I› found  it.   I have absolutely no idea› if this mod works so  you're  on  your› own.  -  Grant  -  8  BIT Librarian of› MAGIC.) (Editor, DITTO! OHAUG  AND  I,› are  not  responsible  if  it  doesn't› work! A.P.)› › DESCRIPTION››      One  possible failure of an ATARI› 1050   disk   drive  that  will  cause› endless boot errors is  a  failure  of› the  sensor  that  detects if the read› head   is   parked.   This  sensor  is› currently NOT reaadily AVAILABLE as  a› replacement  part,  but  MUST  be   in› working  order  for   the   drive   to› operate.   This  article will help you› to   replace  it  with  more  commonly› available parts.›› TOOLS NEEDED››   #2 Phillips head screwdriver›   #1 Phillips Head screwdriver›   30 watt maximum soldering iron›   Small flat blade screwdriver›   Small needle nose pliers›   Epoxy or equivalent glue›   Xacto Knife›› COVER REMOVAL››      Turn the 1050  on  its  back  and› remove  the  6  phillips head screws. › Carefully turn the drive back onto its› feet and set it down.  Gently lift the› back   of   the  cover  and  slide  it› forward. The front bezel will come off› with it.›› DIAGNOSIS››      The  head  assembly   slides   on› tracks  and  is  driven  by  a stepper› motor located to the right of the disk› platter.  The head assembly has an arm› that sticks out to the left.  This arm› slides into a u shaped sensor when the› head is retracted.›      Connect power to the drive but do› not  attach  it to the computer.  Turn› the drive on (do not put a disk in the› drive).   As  the  drive  powers up it› must find the  location  of  the  read› head.   If the head is parked, it will› index the head forward until it clears› the sensor and then repark it.  If the› head was not parked, it  will  retract› the head until it is parked.›      If  the  sensor  is bad, the head› will index forward  1/4  of  inch  and› stop.   Every time the drive is turned› on   the  head  will  index  forward. › Eventually the head runs out of travel› and  will  bang  repeatedly   on   the› forward  stop.   When  connected  to a› computer, you get a boot error because› the  drive  cannot   find   the   boot› sectors.›      As  a  final test, disconnect the› J10 connector on the  circuit  board. › Do not pull on the wires!!!!!  Use the› needle nose pliers.  It is the next to› last connector on the back left of the› circuit board.  When the connector  is› removed, 4 pins will be exposed on the› circuit board.   Jump  the  front  two› pins on the board together and turn on› the  drive.   If  everything  else  is› alright   the   head   will  begin  to› retract.  As soon as the  head  begins› moving,  turn the drive off and remove› the jumper.  If the head did not  move› backwards  then  the problem is in the› circuit board or the  stepper  motor. › That  is  beyond  the  scope  of  this› article.›› DESCRIPTION OF THE SENSOR››      The  sensor  is  composed  of  an› infrared  LED  and  an  infrared photo› transistor.  Either one  of  the  pair› could be bad.  I have not found direct› replacements for  them,  but,  a  pair› made  by  Radio  Shack will work.  The› LED is part number  276-143A  and  the› receptor  is  part  number   276-145. › Please  note,  these  parts are larger› than the original parts and  will  not› fit into the existing sensor housing. › You will have to fabricate  a  housing› for them.›› PROCEDURE›› 1.  Remove the sensor from the drive. › The wire tie  to  the  frame  must  be› cut.›› 2.   Cut  the  sensor from the wires. › Orient the plug  as  it  goes  in  the› drive.   Place  shrink tubing over the› wires and then solder the parts to the› wires  as  follows.  The order is from› front to back.›› 1st wire-emitter of part 276-145›› 2nd wire-collector of 276-145›› 3rd wire-cathode of 276-143A›› 4th wire-other lead of 276-143A››       After  soldering,  position  the› shrink tubing over exposed connections› and heat it.›› 3.   Plug  the J10 connector back into› the circuit board.›› 4.    Fabricate   a   mounting    that› positions  the  LED vertically looking› down.  The mounting must have fore and› aft  adjustment  and  position the LED› above the arm on the head  unit.   The› arm  on  the head unit must pass under› the LED.  Ideally,the photo transistor› pair    should   face   each   other. › Unfortunately,  there  is  not  enough› room under the arm for thr  receptor. › By  trial  and error I discovered that› the receptor  can  be  placed  on  its› side.   The  LED  though  must   shine› directly into the receptor.›› 5.     Fabricate   a   mounting   that› positions  the  receptor  horizontally› looking toward  the  head  mechanism. › The  mounting  must  have fore and aft› adjustment and allow the  arm  on  the› head  unit to pass over it.  I cut the› original housing into pieces and glued› the  LED and receptor to halves of the› mounting.  I then  used  standoffs  to› set the parts to the correct height.›› 6.  Turn  the drive  on.  As the drive› powers up it will  position  the  head› over  the  sensor  pair.   If the head› will not position, check to make  sure› that    the    wires    are   properly› connected.›› 7.  Now that the head is being parked,› make  sure  that  it  is parked in the› proper place.  As a starting  position› the  back  end  of  the head mechanism› should be 3/8  of  an  inch  from  the› inside  boss  that holds the arms that› the head slides on.  If  the  location› is  wrong, turn the drive off and move› the sensor pair as required.  When the› drive is turned back on it will repark› the head.  Continue moving the  sensor› pair until you get the 3/8 dimension. › The sensor pair is only moved with the› drive powered off.›› 8.   Connect the drive to the computer› and attempt to boot a disk.  SPARTADOS› is  less  sensitive  to  head location› than DOS 2.5.  If the disk boots,  run› some  programs to check that the drive› can read all  disk  sectors.   If  the› drive can not read all sectors or will› not boot then move the sensor  pair  a› little  forward  or backwards.  My two› drives both held a dimension  of  7/32› of inch on the gap referenced above.›› 9.   Be  patient.  Eventually you will› get the correct gap.   Reassemble  the› drive cover and you are finished.›               =-=-=››