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Disk II Analog Card: What am I Missing?


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#1 DistantStar001 OFFLINE  

DistantStar001

    Star Raider

  • 77 posts

Posted Fri May 18, 2018 12:03 AM

I recently acquired two Apple Disk II drives for my Apple //e.  I was able to determine that both drives work, except one (now drive 2) has a bad analog board (I swapped the boards to make that diagnosis).  When I examined the defective board, I noticed that a chip (74LS125) had a big chunk of it missing.  I've replaced the chip, but there's been no improvement.  I was told that the kind of damage the chip suffered could have been caused by a short, but I couldn't find any.  All the capacitors seem good, and I can't find any broken traces.  I'm kind of at a loss now.  I mean one drive is better than no drive, but I'd like to get both working if I can.  Maybe someone can spot something I missed.  (The first photo pre-repair.Attached File  IMG_0120.jpg   1.45MB   3 downloadsAttached File  IMG_0128.jpg   1.4MB   3 downloadsAttached File  IMG_0131.jpg   1.42MB   3 downloads 



#2 trash_44fr OFFLINE  

trash_44fr

    Space Invader

  • 34 posts

Posted Sun May 20, 2018 8:17 AM

Hello,

In fact, the LS125 will blow up if it takes 12 Volts instead of 5 which happens when the 20 pin connector is not correctly plugged in the Disk II controller card (ie shifted by one pin).

Since you have one working card, I suggest you tried every single IC of the defective one on it. There is good chance you'll spot more damaged ICs.

Cheers,


Edited by trash_44fr, Sun May 20, 2018 8:18 AM.


#3 Keatah ONLINE  

Keatah

    Missile Commander

  • 21,586 posts

Posted Sun May 20, 2018 8:31 AM

Ensure all your connectors and contacts are clean.



#4 DistantStar001 OFFLINE  

DistantStar001

    Star Raider

  • Topic Starter
  • 77 posts

Posted Sun May 20, 2018 2:16 PM

Good to know, I've actually done that before.

#5 DistantStar001 OFFLINE  

DistantStar001

    Star Raider

  • Topic Starter
  • 77 posts

Posted Sun May 20, 2018 9:24 PM

Hello,

In fact, the LS125 will blow up if it takes 12 Volts instead of 5 which happens when the 20 pin connector is not correctly plugged in the Disk II controller card (ie shifted by one pin).

Since you have one working card, I suggest you tried every single IC of the defective one on it. There is good chance you'll spot more damaged ICs.

Cheers,

Thank You Space Invader!  I was able to narrow it down to the chip marked MC3470P Motorola 8045.  Can you believe that someone actually threw these things away for what's likely to be less than $4 in repairs.  Whoever it was kept the Apple II, but couldn't be bothered to fix the drives!?!  I don't get it :-\



#6 Osgeld OFFLINE  

Osgeld

    Quadrunner

  • 5,765 posts
  • Location:Nashville, TN

Posted Sun May 20, 2018 9:42 PM

I get atari consoles all the time "broken" that just requires jiggling the power switch ... if people are not going to wiggle a switch they sure are not going to sit down and trace a circuit fault





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