Disk II question

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It's been so long, and of course, back in 1980 all I had was my Apple disk II drives so my memory might be fading about how good they were compared to others. I mean, who had 2 or more different computer systems with disk drives back then? However, it seems to me that the venerable Disk II leaves just a little wanting.

My drives will only format about 50% of the brand new, still sealed in the box Memorex SSDD floppies that I got. Neither drive is better than the other and both are very gently used, clean as a whistle and test out just fine with any diagnostics I run on them. Here's the rub, my similar vintage Tandy COCO (uses the same drives as the TRS-80 Model 1 and formats them at a similar capacity to the Apple) has no problem formatting and using the ones the Apple can't cope with. To the COCO they are all just fine and dandy.

Now, I don't doubt Woz for a minute, but is it possible he left a little something on the drawing board when he designed the Disk II system? If so, is there a way to increase their performance?

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speedyG's picture
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Re: Disk II question

Hello BillO,

allthough mentioned several times previously :

http://www.appleii-box.de/H084_1_AppleIIDiskService4.htm

In fact there are several adjustment points to fix problems....

if the speed and track allignment pass without trouble like you mentioned
and which i explained in the pages before the mentioned page above....

there is a chance that the adjustment of the MC3470 might have drifted off the specified limits....
this may be adjusted with use of an oscillscope...
.
in such case its also highly recommended to download the DISKK II Factsheets from SAM´s:
http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Books/Sams%20ComputerFacts%20-%20Disk%20Drive%20Apple%20II.pdf

There are quite good pictures taken from scope while performing measurements and displaying the
way signals should look alike ( and in that manual you can zoom into that pictures )...

In fact the DISK II does not exactly treat disks the same way that other drives do, that have been
launched into the market later.... the later models use MFM method for read/write process and
most later drives perform that with special controller chip....

When DISK II was invented and introduced into the market this chips did not exist
or have been that damn expensive that WOZ used another way of treating the disks
in the drive with simple logic and analog chips instead,
to keep the DISK II at affordable pricing to the customers...

other point is aging of the disks....
allthough you mention them to be new and "right out of the factory box"..
i´m sure you can´t make proof the way they have survived in the storage....
diskettes like to be stored in cool area ( 5 degrees to 10 degrees Celsius - but not below 5 degrees Celsius ! )
and not too dry ( humidity from 20% to 35% )
if it´s too dry or too hot the basic carrier loses over the decades it´s flexibility
and the magnetic coating looses it´s adhesive power to keep at that surface....

the later used MFM method of reading from and writing to disks is rather more tolerant
to weakness of disks aged by storage... DISK II is a bit more critical to that conditions...

speedyG

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Re: Disk II question

Thanks for the information SpeedyG!

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Re: Disk II question

So, here is something other DISK II owners might want to try. I was rummaging through my TTL parts bins looking for de-mux chips and I came across a few 74ATC125 chips. Shrugging at the tiny thought that popped into my head I took one and sauntered over to a DISK II unit I had un-clothed for pre-alignment purposes and replaced the 74LS125 on the analog board with the 74ATC125 and tried to INIT a disk that failed several times before, and voila! It worked! Further, I was able to recover about 60% of the disks that failed earlier. This was all before a pipe spontaneously sprung a leak in the master bedroom en-suite, but that is an entirely different story.

Not 100% verified that the 74ATC125 is better or that the 74LS125 was a marginal unit, but I went ahead and put one in both my DISK II units. Just thought you might like to know. If others can corroborate the effect, it's a real cheap upgrade.

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Re: Disk II question

Hi BillO,

Did you mean 74ACT125 ?

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Re: Disk II question

Yes, 74ACT125, that's the one. A touch of type-too-fast-dyslexia got the better of me.

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Re: Disk II question

OK, 74ACT125 ordered.
I will let you know if my bad originals will lived again !

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Re: Disk II question

Hello,

I have tested the ACT version of the 125.
I see no difference at all with my disks, both dead or working.

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Re: Disk II question

I did a run with a scope. Here's what I found.

One one of my drives (the least reliable initially) I put back in the 74LS125 that I took out and the scope signals we lousy. The chip must have been partially damaged at one time by a bad cable insertion. The original 74LS125 from the other drive exhibited much, much better signals. The 74ACT125 has slightly nicer signals, but not a ton better. I'm guessing any performance increase is purely marginal, it it exists.

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Re: Disk II question

See my responses in:
http://www.applefritter.com/content/a9m0107-intermittent-failure-copy-disks-dos-33-system-master-program

I also noted in some recent DISK II units I worked on that the analog pcb to stepper motor connector seemed a little more prone to developing a high resistance. It's easily cleaned and I did this on one of my first DISK II units when I took it apart for a photo op. I did so because I thought I heard some weakness when the drive wanted to snap the head between tracks. It may have been nothing, but with being 35 years old and all that I figured what the hell. You know? It may have been nothing. But this particular unit ran my AE and BBS in old days practically non-stop.

In any case, a reseating of chips and cleaning of contacts and connectors is a good thing on a heavily used drive that was banged around a lot. It works perfectly and passed a full alignment, diagnostic, and practical test.

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Re: Disk II question

BillO wrote:

I did a run with a scope. Here's what I found.

One one of my drives (the least reliable initially) I put back in the 74LS125 that I took out and the scope signals we lousy. The chip must have been partially damaged at one time by a bad cable insertion. The original 74LS125 from the other drive exhibited much, much better signals. The 74ACT125 has slightly nicer signals, but not a ton better. I'm guessing any performance increase is purely marginal, it it exists.

Bad conduction/oxydation is rather often a problem - dependent to the area the DISK II has been working in the sum of the years.... in areas close to seas and bayareas close to the osean the high humidity and probably also salty humidity even might enforce such trouble..... so cleaning contacts and pins while reseating is always a good idea...

It also turned out - to my measurements at least - that the rainbowcales performed worse than the gray cables that are at leats at on side shielded.... they perform better - and at the grey partially one sided shielding cables you can be sure that they have the precisely determined length. At the rainbow cables i have seen many that have been made "homebrew" with a large renge of variety of lengths not same as the original cables....
cables with length beyond 2 feet do make trouble....

Another trick i´ve learned while making short term practical education - while studying - at Messer Griesheim ( they manufacture commercial transmission satelites ) is to apply some thin amount of baby vasiline to contacts before joining them back together. Sounds simple - but think twice about it - in fact when the contacts get joined together the contacts sweep the vaseline besides and the remaining rest fills area around the contacts and thickens by aging and by that prevents contacts from further later oxydation. This habit was performed every time PCB´s where joined together at satelites to keep electrical contact healthy for years. I perform this treatment too and it served at least for me well during the last decades.... drives that i performed service years ago are still working in perfect condition....

And of course for "long term service" i really recommend the adjustment of the read/write circuitary - it´s a time eating task - but it just must be performed one time each 20 or more years....

and of course a checkout for good grounding contacts....

speedyG

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Re: Disk II question

For those of you that don't know, the DISK II units with the grey cable have a good grounding and RF shield. The grey cable attaches not only to the interface card, but clamps to the backplate of the computer. It was a little tedious to set-up but worked well.

The rainbow cable was longer and provided next to nothing for shielding and ground. It's a wonder they worked at all.

And there was a 3rd party company that sold extension cables, rainbow cables, that were meant to extend the short grey cable. And of course the grey cable's performance was axed by the extension.

And finally we have the DB style cable. Like in the duodisk. OR plastic-housing-disks. It has good electrical performance, but the "pins" in the female part (attached to the controller) IMHO are a little bit flaky. I cleaned and tensioned mine 2 years ago. And this fixed up the obvious intermittent behavior. Been flawless ever since.

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Re: Disk II question

I applied automotive bulb grease, which is essentially a keep-the-water-out dielectric compound. Costs $4.00 and lasts for maybe 30 Disk II refurb jobs.

I'm a little hesitant to use petroleum jelly vaseline because of the petroleum distillates. I don't trust that on all plastics.

It all works by displacing the air and oxygen around a contact. There is always some air and O2 trapped, but it's so minuscule it gets consumed in the oxidation process immediately. Anyways, smear the stuff on and you have a barrier. Now when you make contact, both contacts penetrate each other's jelly shields and form a new one encompassing the touching metal pieces. And the contact never touches atmosphere again. Never corrodes anymore. Never becomes intermittent.

TV tuner/cleaner does something similar but flows into areas you can't get a swab into. But it isn't as long lasting.

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