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zastin17

macrumors newbie
Original poster
Nov 24, 2017
18
9
Ok, I need some serious help with my 1984 Macintosh 128K Guys!!

I put this on a shelf for almost a year. Wishing it worked, but never being able to Re-align the 400k drive again. I am sad
😥


To start off, A few years ago, I found this incredible condition 128K Macintosh set. All Factory stock, black Flyback cup, ect. Brand new condition bag, mouse, keyboard, everything!!

My dream, trophy Macintosh!!

It didn't read disks at all or was misaligned at first.
I also have some later Macintosh with 800k drives.

I made a 400K disk inside of one of those machines, and spent almost a entire day power cycling the 128K Macintosh, while moving the alignment PCB on the 400k by hair amounts using the disk made on the 800k drive.

By some amazing and incredible miracle, one of those attempts resulting is a perfectly aligned drive!! And I mean perfect.
The 400K read and wrote all disks from all the other machines absolutely perfectly for over 2+ years after that! I was happy
😁


This lasted a long time. A year ago, I was doing some projects with a later Macintosh Classic drive to put more software on the 128K. Using the large drive going to the 800k, then into the 400K. U successfully got all the original 1984 software, like Macpaint, or the Demos onto some 400k floppies for the 128K

And while I was swapping disks, the 400k began throwing Read and Write errors. It still managed to boot, but had obviously became ever so slightly "misaligned" having some issues with many of the disks all of the sudden. Cleaning the head did nothing either.

So I made the dumb decision to loosen the Alignment screw AGAIN!!
Expecting myself to hit the lottery again

And guess what, It never worked since.
😥


I need help aligning this drive. I'm so close for this Macintosh to be back at 100% perfect again!!
I do have an Oscilloscope I can use, but I don't know where to start with this drive. Is the drives head just a coil? Do I just probe the head?

Here are some pictures from yesterday I just took, and several from Years ago when the drive was aligned by sheer Luck.

I have the Macintosh ready for when I figure out the best way to go about doing this. I JUST REALLY NEED SOME HELP. THERE IS VERY LITTLE ABOUT THESE DRIVES ONLINE.

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MacTech68

macrumors 68020
Mar 16, 2008
2,387
207
Australia, Perth
Firstly, whilst there is a Gain & Phase adjustment for the read amplifier, I've yet to see one that required any sort of adjustment. The circuit seems to be similar to a Disk II floppy drive (ie, based around an MC3470).

I'd rather point to some potentially simpler checks first.

A video of the head moving from an inner track to track zero might reveal suspect stepper worm drive bearings. A long seek of the heads should be a smooth tone without odd/random stutter (until it reaches the fullest extent). A drop of oil on the bearings (front and back of the stepper motor) should suffice.

The rails that the head assembly run on should be clean and NOT oiled in any way.

Do check that the felt on the head 'clamp' is not missing. Here is what one looks like:

400K drive upper felt pad 2.jpg


Do you have another 400K drive? If so, you could swap it in to check if the RC network "filters" on the motherboard have failed.

Resist loosening the screws on the stepper motor.

Other wise, try aligning the track zero again - use the reset button on the motherboard rather than power cycling. Use a flatblade screwdriver wedged into the notch on the drive chassis below the track zero sensor PCB and lean the screwdriver left or right to slowly move the track zero sensor PCB.

EDIT: In case I've missed anything, have a look here too:


EDIT 2: Just realised, that was YOUR original thread - DOH! :oops: :confused:
 
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