Aligning an Amiga Floppy Drive Using an Oscilloscope

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I didn't give up on the crusty Amiga 1000 drive. Let's try harder to help my friend Brad keep his A1000 original, and at the same time develop a procedure for using an oscilloscope to align floppy drives.
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Опубликовано:

30 сен 2024

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Комментарии : 20

@rafaellarios3707 2 года назад

I remember that TP1 and TP2 are actually the differential outputs of r/w head amplifier. Hook up scope channel 1 to TP1, channel 2 to TP2. I guess channel 2 was "inverted" and both channels "added" together. You needed another test point (index signal) to hook up your external trigger to keep alignment pattern steady. There is only one amplifier because only one r/w head can operate at a time. You should be able to "see" either head on same test points by having the drive exercising software switch r/w head. For proper alignment there used to be analog alignment diskettes by Dysan and Memorex. There was a cat eyes pattern for track alignment. There was also an azimuth alignment pattern somewhere. As long as you don't loosen the screws fastening the upper head, you should be ok by just aligning the fixed head. It's been more than 30 years ago since I did this. Thank you for your video, it brought back some good memories. Rafael

@krnlg 2 года назад

I guess in that case the cycling between stronger and weaker signal shown on the oscilloscope was to do with one head not being as well aligned as the other? Interesting stuff.

@rafaellarios3707 2 года назад

@@krnlg Cat eye pattern looks like two "lobes" resembling a pair of "cat eyes". When R/W head is perfectly aligned, the two lobes exhibit equal amplitude. Maximum misalignment allowed was when smaller lobe had 70% of bigger lobe amplitude. Assuming properly aligned R/W heads, it may happen that one head may exhibit smaller cat eyes pattern amplitude than the other head and yet both R/W heads are OK. My observation back in the day was that the "fixed" head signal was stronger than the "movable" head perhaps due to lower pressure on the surface of the disk. This movable head had to separate from the fixed head at floppy disk insertion and ejection time.

@HelloKittyFanMan Год назад

Also, why can't the stepper motors and TZSes on all these drives, both 3.5" and 5.25," be fastened so hard at the factory with a glue along the screw slots so tightly that the stepper is never strong enough to slide the heads back hard enough to knock either thing out of calibration?

@retrofriends Год назад

I did this video a long time ago, but if I didn't mention it, the screws are actually lock tighted in place at the factory. They are that way on all drives that I've ever seen. But that doesn't help protect against the computer being thrown in a dumpster, or whatever else banging around may have happened.

@HelloKittyFanMan Год назад

@@retrofriends: Oh, sorry if I missed it. But if they are glued with something made by Loctite then what is it that lets something like a Commodore 1541 still break that and re-zero-bang its head out of alignment? How is it not proofed from that?

@HelloKittyFanMan Год назад

Hmm, I was never really aware that 3.5" standard floppy drives could get misaligned. I bet this would be even harder to do with those small horizontal steppers. Way back in the day we first had DSI here in Utah align our Commodore 1541. Then a few years later we found the disk "1541/1571 Drive Alignment," and it instructed me as a mere 11- or 12-year-old to run the software and use that calibrated disk while doing what you're doing there, turning the case and stator of the stepper motor until the software told me I had the stator matched up to about the middle of where the head was on that track... or something like that. But I wish we could've done it with an o-scope! Also, I have a hard time imagining how moving the TZS would work, unless it gets knocked farther back from where a properly adjusted have theirs, because if those don't match from drive to drive then it seems to me like a disk written with one drive won't work on this one, or/and vice versa. How would moving the TZS bring it back to spec.?

@retrofriends Год назад

Either in this video or the previous one, I make the point about the track zero sensor position and the radial position of the motor making the exact same effect. This is true because if you move the track zero sensor you move where the drive thinks track zero is, and all other tracks are skewed along with it. This is exactly the same thing that happens if you rotate the motor.

@HelloKittyFanMan Год назад

@@retrofriends: Hmm, I can't really envision that. Oh wait a minute. Don't drives like Commodore 1541s get misaligned because they _don't_ have a TZS, so they head-bang instead? So you're saying that really the only reason these would get misaligned is because of a hard drop or something like that? How would it be hard enough to break that sealant? And does your other video have a diagram that shows why moving the sensor would not give the drive and alignment that is unique from other drives because it's non-factory?

@retrofriends Год назад

@@HelloKittyFanMan It wouldn't break the sealant as much as cause something else to bend or tweak. Not hard to do since we are talking about micron increments making the drive faulty. There's also other potential causes like temperature and humidity swings, electronic drift caused by aged components, and poor build/qc from the factory. Some drives will be irreparable due to wear, mechanical, and electronic failure. I always kept that in mind when I was trying to get drives to work. Who knows, I could have even gotten a worn drive to work by dialing it in better than it was at the factory.

@TheMcflyster 3 года назад

Great video man! We dident see the testpoints on the drive thou. That would be intresting to know.

@retrofriends 3 года назад

I mention they are clearly labeled, no trouble to find.

@HelloKittyFanMan Год назад

Now please show us how to align a *Zip* floppy drive! Maybe those drives that are harder and harder to find without the "click of death" can be "resurrected" that way!

@HelloKittyFanMan Год назад

"We can go vertically up." As opposed to some sort of "horizontal up"? 😛

@HelloKittyFanMan Год назад

"You're booting off of a ROM." So if you're booting _off of_ a ROM, then what are you booting *from* instead?

@HelloKittyFanMan Год назад

That's pretty cool, thanks for sharing!