Apple Disk II Schematics

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Apple Disk II Schematics

I noticed one of my disk speed is 40% slow according to APTEST. I attempted to tweak it up by adjusting one of the two potimeters on the circuit board, however, it seems with it all the way counter clockwise won't allow it to get better than the 40% slow.

Anyone having a good quality schematic of that circuit board in the disk II drive? If you have the ability to force the schematic color so it is white on black background that would be most helpful.

Also, what does the other potemeter do?

Thanks
-RocketScientists

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Apple Disk II Schematics

Apple published the schematics of both the Disk ][ controller and the Analog card in "The DOS Manual" (pages 145 and 146). According to Jim Sather in "Understanding the Apple II" (page 9-9) when Apple updated DOS from 3.2 to 3.3 the 2us delay between peak detection and read pulse output turned out to be too short for the new format so Apple replaced R21 with a potentiometer and this is adjusted for ~3us delay. I don't think adjusting this will help with your speed problem.

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Thanks for this info

Thanks for the explanation. I found the correct pot (on back of the drive itself) and adjusted both to the 200ms mark.

Both trip potometers needed some "clean" wiping. When doing this, I used a "reference" Apple Disk to get them back to alignment. without an oscilloscope, I was able to get this with some trial and error.

Thanks again for the publication pointers. I will look at them. I did notice the 3us had the one-shot timer chip+mica capacitors. I figured they were timing elements.

Thanks again,
-RocketScientists

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