Recently I've been doing some maintenance on my Apples, and one of the things I've been having trouble with is tuning up the duodisk. While the Disk ][ has plenty of documentation and techincal manuals, the duo seems to be a bit sparce. I'm aware of the speed pots on the bottom, but what about head alignment/radial adjustment? Carriage limiter? Azimuth?? I do have a copy of APTEST, but I've been unsure as to what screws to turn to adjust the heads. That and the lack of detailed tech docs have left me in the dark. Any thoughts? Thanks!
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Made the obvious discovery that the duodisk is really just two 5.25 unidisk units. Once again confused on how to adjust the head position, and any manual I can find doesn't state how. Hmmm.
I also have a diodisk, and i have so many issues with it, i started to look at docs but couldn't find any. But i am happy that SOMEONE actually asks this question
... what you can do is to replace all the electrolytic capacitors, which after a few decades are the most likely culprit for failures of electronics. Check for corrosion on the PCB traces below or near the electrolytics.
You may also change digital ICs (if socketed). Do not change the read amplifier IC (yet) --- if you do this, it may require some adjustments to trim pots you can't do without the service manual (and other means) you don't have.
You should also inspect the head for dirt - typically, brownish residue. Head can be cleaned with Isopropyl alcohol wetted Q-Tip. Do not use "head cleaning" diskettes - these have deteriorated, too, and may cause damage to the head. Note that trying to load even one deteriorated diskette can easily gum up the head again to an extent that even good diskettes will not read anymore after that, and worse, the "good" diskette may now be scratched and bad, too.
Do not try to adjust anything mechanical like head positioning / head azimuth ... in 40 years refurbishing old computers I have had not one case where azimuth adjustments were necessary. In most floppy disk drives the head is adjusted in the factory and then glued in. No way to adjust anything ! Azimuth adjustment required a specially formatted adjustment diskette which nowadays are unobtainium and would have deteriorated to uselessness anyways.
The head positioning mechanics may be worn out, especially on floppy disk drives having no track zero sensor, and depending on the type a steel band may be involved, which has stretched. This steel band typically is fastended by screws both to the head sled and the stepper motor drive wheel. In some cases the screws can be loosened (depends on the thread glue they may have used) and the band can be re-tensioned. But getting the track positioning right after such a manupulation is very tricky. So, any such manipulation must be a means of last resort and only if a track positioning problem has been proven by measurements, for which you need an oscilloscope and a known good, formatted diskette.
Using these rules of thumb, my success rate for refurbishing floppy disk drives was about 50% or so. These are bad odds. But it is what it is. Beginning with the mid 1980s, floppy disk drives got so cheap that manufacturers stopped furnishing service manuals. It was expected to swap a defective floppy disk drive against a new one and throw the old one away. Consequently, they started to design the floppy disk drives such that they could not be taken apart for repair anymore. I remember some direct drive ones where it was impossible to remove the PCB for the direct drive spindle motor, and so it was impossible to replace bad electrolytics on that PCB. Landfill economy ...
- Uncle Bernie
I'm not exactly sure what is broken or how you tried to test. Apple floppy drives don't typically need much mechanical attention except fort the occasional minor speed tweak. The good news is drive one probably got 80% of the use and drive 2 will seem much "newer ", swap the drive positions and see if that helps. Then you have enough working to better test the more worn drive.
Nothings broken, just wanted to do some general maintenence :) I've only used APTEST, and once I run the test again i'll provide the numbers it gives me. However, if the general concensus is that a speed refinment is all that's needed, I'll only do that.
This is the way to go - make sure the speed is calibrated correctly, make sure the heads are clean and only then check to see if alignment is fine.
I would NOT touch the alignment unless there are read issues between drives - that is, a disk written on one drive is not able to be read on another drive, but a disk written on one drive is able to be read back on the drive that wrote it.
So if you can read all the diskettes you have (especially something commercially produced) then DO NOT ADJUST alignment. You stand a greater risk of making something way worse than before you started.
The alignment utility in APTEST can only test RELATIVE alignment, that is, alignment vs a known quantity. IE: Can it reliably read a disk written by another drive?
(Trying to use APTEST to align a drive using diskettes written using the same drive is a useless exercise.) This shoudl be convered in the instructions included in the APTEST disk.
That said, APTEST's alignment utility is the only comsumer-grade alignment utility that can test alignment without special tools, but you do need known-good disks written by a known-good drive.
100% agree with baldrick here. Alignment is something best not messed with unless it is obviously out of whack.
I would slightly disagree with not messing with the alignment, as with mine I have to sometimes "jumpstart" the drive to get it to read, and even then it's a 50/50 if that works
That may or may not be an alignment issue. Does the drive reliably read diskettes it wrote itself? If you still need to "jumpstart" with self-written disks then alignment is not at fault, but some other mechanical or electronic issue at play.
Well I'm back, I purchased an authentic copy of DOS 3.3. Using APTEST, and using the 3.3 disk, I got Fraction Right=1, Diff Frac= -.04, Diff Frac Going=-.44, and Diff Frac coming=.46 on the left drive and Fraction Right=1, Diff Frac= -.85, Diff Frac Going=-.89, and Diff Frac coming=-.81 on the right drive. Do these sound like acceptable numbers?
The most important number here is "Fraction right" which when it is a value of 1 means it got the track data 100% of the time.
The instructions on APTEST say that the other numbers "going" "coming" are results from trying to read between tracks. They are the fraction of times the higher track was read minus the fraction the lower track was read when the head is advancing (going) or retracting (coming).
The number should be less than 0.1 for a diskette that is aligned perfectly to the drive. Typically a perfectly aligned drive should have these numbers between 0.1 and 0.2, but this is not vital.
Drives can read reliably even with high-ish numbers "going" and "coming".
The instructions also say that if you are getting results greater than 0.9 on the "going" or "coming" test then that means the drive is reading track data when it should be reading the blank area between tracks. So your drives may have slight mislaignments relative to this commercial DOS 3.3 diskette.
If you test the alignment with a diskette that was formatted and written on the same drive you're testing, you should theoretically get "1" for the "Fraction Right" and 0.1-0.2 for the "going" and "coming". This is expected because APTEST only tests RELATIVE alignment based on the diskette you inserted in it.
My opinion on the matter at hand is this: Run the alignement test in APTEST on a large sample of the everyday-use diskettes you have on hand that you plan to use regularly. If your "fraction right" is 1 for all of them then leave the drive alone. You will stand a greater chance of making it worse than making it better if you dick around with alignment.
The worst thing you can do is align your drive to some arbitrary standard and the end result is that you cannot read any of your everyday disks afterwards.