Disk III Analog PCB Troubleshooting

Disk III Analog PCB Troubleshooting

DESCRIPTION: Use this procedure only if a Disk III Analog PCB problem is
confirmed.  To obtain the procedure to confirm a Disk III problem, search on
"HTS and Disk III and General".
 
YOU WILL NEED:
1. The following Disk III Analog PCB chips:
   * IC 2003 (APN 327-2003)
   * IC 74LS125 (APN 305-0125)
   * IC CA3146 (APN 351-3146)
   * IC 3470 (APN 355-3470)
   * IC 74LS74 (APN 305-0074)
   * IC 74LS32 (APN 305-0032)
2.  Disk alignment aid
3.  Level I Tech Procedures binders
 
BEFORE YOU START:
1.  Refer to the Technical Procedures if removal/replacement or adjustment
    procedures are needed.
 
 
2.  Before replacing a component on the Analog PCB, make sure that the power
    is off and remove the Analog PCB.
 
 
3.  If replaced module/part doesn't fix the problem, reinstall the original
    module/part.
 
INSTRUCTIONS:
1.  Remove the problem drive's case to expose the Analog PCB.
2.  Examine the Analog PCB for:
    * R32 at location D1 missing (send to Apple)
    * IC 74LS74 at location E1 missing (replace)
    * Jumper wires soldered to back (send to Apple)
    * Damage (e.g., burns, cracks, etc.) if board is beyond repair, throw
      it away. Examine each chip and its socket.
    * If repair is possible but it can't be made by replacing a socketted chip
      send the Analog PCB to Apple.
3.  Find the PROBLEM below and perform appropriate FIX.
 
   PROB: Known good internal Disk III in test bed Apple III won't boot when
         the problem drive is installed externally
    FIX: Recheck for the problem after each of the following steps
     (1) Replace IC 2003 at location C4
     (2) Replace IC 3470 at location B1 and IC 74LS125 at location G2
         then if it boots, perform the comparator offset adjustment
     (3) Replace IC 3146 at location A3
     (4) Replace IC 74LS74 at location E2
     (5) Send the Analog PCB to Apple
 
   PROB: Drive will not perform the D-Speed adjustment
    FIX: Recheck for the problem after each of the following steps
     (1) Replace IC 3470 at location B1 and IC 74LS125 at location G2
         then perform the comparator offset adjustment
     (2) Replace IC 3146 at location A3
     (3) Replace IC 2003 at location C4
     (4) Replace IC IC 74LS74 at location E2
     (5) Replace IC 74LS32 at location F1
     (6) Send the Disk III Analog PCB to Apple
 
   PROB: Drive does not come on.
    FIX: Recheck for the problem after each of the following steps
     (1) Replace IC 2003 at location C4
     (2) Replace IC 74LS125 at location G2
     (3) Send the Disk III Analog PCB to Apple
 
   PROB: Drive with the problem Analog PCB installed reads but doesn't write
    FIX: Recheck for the problem after each of the following steps
     (1) Replace IC 74LS125 at location G2
     (2) Replace IC 2003 at location C4
     (3) Replace IC 3146 at location A3
     (4) Send the Disk III Analog PCB to Apple
 
   PROB: Drive writes when the disk is protected
    FIX: Recheck for the problem after each of the following steps
     (1) Replace IC 74LS125 at location G2
     (2) Send the Analog PCB to Apple
 
   PROB: None of the symptoms above match those of the problem
    FIX: Recheck for the problem after each of the following steps
     (1) Perform the D-Speed adjustment
     (2) Replace IC 3470 at location B1 and IC 74LS125 at location G2
         then perform the comparator offset adjustment
     (3) Replace all socketted chips one at time
            * IC 2003 at location C4
            * IC 3146 at location A3
            * IC 74LS74 at location E2
            * IC 74LS32 at location F1
     (4) Every chip on the PCB has been replaced.  If it still doesn't
         work, send the Analog PCB to Apple.

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