Tonight I'm doing an in-depth diagnostic of one of my early DISK II drives.

[Keatah]

Tonight I'm doing a diagnostic of one of my early DISK II drives. It is not the very first one I had, but one purchased a year later.

 

This is to be an in-depth physical examination and performance analysis.

 

DIAGNOSTIC DISK TESTS:

Speed

Write protect

Speed consistency at inner, middle, and outer tracks

Noise tolerance

Write, then read at inner, middle, and outer tracks.

Track alignment for tracks 0-23

Sector skew

Positioner backlash hysteresis

Disk clamping

Walking bit test, including complement

Half track positioning

Quarter track positioning

Erase crosstalk

Half track crosstalk

Sync mark test

Weak signal read

Write protect switch test

Intertrack timing consistency

Sector latency test

Zero write

Frame bit test

 

SCOPE AND DMM TESTS:

Read pulse shape verification

Write amp output level test

Read amp input/output level test

Data register and logic state sequencer test

PCB voltage level test

Stepper motor voltage and resistance test

Drive motor voltage and resistance test

Head resistance test

Controller clock test

Device Select test

General logic levels verify

Crossover distortion

Pulse width duration

Azimuth adjustment check

Electrolytic capacitor test

 

INTERNAL PHYSICAL INSPECTION:

Electrical connectors/contacts cleanliness inspection

Head cleanliness

Overall solder condition

Carriage rail inspection and OEM re-grease

Pressure pad fluffiness and cleanliness

Drive belt exam and cleaning

Head carriage inspection

Check for frayed or chaffed wires

IC socket and seating inspection

 

STANDARD REAL WORLD TESTS WITH COMMON DISKS:

13/16 sector boot and read/write

Fast dos test load/save files (Hyper-DOS, David-Dos, Pronto-Dos)

Standard format in DOS 3.2 , 3.3, Pro-Dos.

Read 30+ year old disks (written by other drives)

Read 30+ year old disks (self written)

Locksmith bit copy test

Nibble test

 

MATERIALS, TOOLS, REFERENCE MANUALS, DISKS:

Dmm

Oscilloscope

OEM grease

Eraser

Contact cleaner

Fluorescent light

Standard screwdriver set

Loc-tite and enamel paint

Sams ComputerFacts packet for Disk Drive Apple II Model A2M0003

Understanding the Apple II Jim Sathers

Locksmith owner’s manual

Beneath Apple DOS

Verbatim Datalife Analyzer Disk

Dysan Analog Alignment Disk

Dymek Recording Interchange Diagnostic Disk

Apple service alignment disk

Various standard disks from back in the day (See above)

 

Results to be posted shortly.

[RobertLM78]

Very comprehensive. I don't even own an Apple II and I'm interested. Sounds like you have some nice equipment to boot.

[Keatah]

I'm about 1/3rd of the way through more or less and things are looking stellar indeed. I don't know the format of any report I might make up, or perhaps just make an OK checkbox, with space to record anything out of specification.

[Keatah]

I'm totally blown away by the results! And yet not surprised. Everything was well within specification, no doubt due to the metal construction and quality components. And conservative design. So forgiving that if things were mis-adjusted the drive would likely continue to function. The electronic components and waveforms and levels seemed to be spot on. The diagnostic disks had not a one failure. Contacts required minimal if any cleaning. Head characteristics all in order. And it got a good cleaning. Track alignment spot on and linear throughout the entire range 0-23. Speed exactly as I recall setting it years and years ago.

 

All the various floppies read just fine with no re-calibration knock or having to re-seat the disk hub/center.

 

Timings and clock signals all just fine.

 

Lots of consistency and little to no hysteresis in electromagnetic, electronic, and mechanical aspects. Except where it's supposed to be.

 

No parts needed replacement but I do have spare drive belts and pressure pads on hand. 2 spares each for each of my Disk II drives, and no more. Yet.

 

More impressive was the amount of use and abuse and vibrations from transporting and BBS operations way back in the day. I always feared this would have shortened the life of the drive. But from the looks of it I'd say it's got another 34+ years with moderate use from time to time. As far as I'm concerned, it performs like brand spank'n new. Remarkable.

 

I would feel completely comfortable using it as modern-day, light-duty, storage device. However it would be impractical to do so with the 143K bytes per side capacity. It would take 15 disks, using both sides, to store 1 compressed image from a contemporary DSLR. But for journals and things like that it would still be suitable.

 

I'm totally convinced that simplicity and conservativeness in design are key points for longevity. And the Disk II drive is a shining example. The lightweight all-metal frame construction and overall generous spacing of componentry certainly contribute to that longevity and as a bonus - makes it easy to work on something. Nothing interferes with other stuff. Parts aren't smashed against each other, or press & snap fitted. Lot's of room to mess around inside.

 

The internal Analog Controller and Speed Controller boards are elegant. Even more so the External Interface Card. This storage sub-system is infused with so much minimalism one is amazed that it works at all. Every component serves a purpose. And it's fast, especially when compared against other drives of the era.

 

It feels fast, too, because there is zero overhead within the disk drive itself. There are no processors to set-up and synchronize with the host. No complex on-drive programs to run. No firmware as we know it today. The Disk II and it's accompanying interface card sport a total IC count of 12. And like many IC's of the day, they are basic logic gates, little more than simple arrays of solid state relays and switches. Complexity on the level of a 4-function handheld calculator. So.. As soon as the host wants some information, the head is moved to the desired track and that's it. The magnetic domains are stuffed into a set of registers which are then placed on the data bus. A parallel data bus. This drive doesn't suck data through an asthmatic straw. No sir.

 

The way of the Apple II and Disk II is that your main program asks DOS & RWTS to get some information. Two motors are activated and data is then presented to the requesting program or dumped DMA-style right into main memory. No fucking around. This kind of setup can be likened to an external robotic actuator in that a robot arm typically doesn't "think" on its own. It is controlled by a host program. The main disadvantage is the user's program stops executing during disk I/O. The main 6502 is temporarily repurposed and now becomes a controller and director. But you gain plenty of speed with this configuration.

 

What's even nicer is that you have no internal power supply or external power brick to contend with..The drive takes so little power that the host can power it just fine. Furthermore, along with the all the low-stressed electronic and other mechanical components, you get fairly large drive and stepper motors. These are oversized given the job they do and therefore run cool without overheating. I remember disk copying marathons from the days of yore and constant BBS activity. The drives never warmed up. And the little heat that was generated was absorbed and carried away by the frame and housing. In fact most of the little bit of heat produced came from the disk-sleeve and disk-head contact friction. And a high quality disk with good surface properties would come out of the drive (after 45 minutes continuous spinning) noticeably cooler.

 

And there you have it. A non-technical look at why the Disk II is so fast and reliable. To lean more about this extraordinary storage sub-system, see the previously listed reference material.

[RobertLM78]

Very cool!

 

This makes me want to do diagnostics of my two TI SSSD drives, but I don't have the equipment or parts, if I need to replace anything. They too appear to be working like champs though, despite being 30 years old.