800K Floppy Drive Head Issue — Track 0 Misalignment?

[JDW]

I have been exchanging dialog with a viewer of my YouTube channel who has been servicing his 800K drives in conjunction with my video on that subject.  In particular, he has two 800K drives which show the head moving all the way to the back but then the heads stay there. If the head is then manually moved with a finger, the head will then go all the way back again and stay there.  He made a couple videos for me, which I have combined into a single video here...

After watching that video, would you say it is a Track 0 misalignment problem?  (If so, that will require removal of the screw holding the optical sensor in place and slowly moving that sensor 1/4mm at a time until the head starts to work normally again.)  If not Track 0 misalignment, what other causes are there?  

It's not a lube issue because he relubed the drive, and it is using the correct cable, and the Mac is know good because he has other drives that work fine on that same Mac.

I had proposed to him that it is most likely a Track 0 issue, but he is hesitant to remove that screw, worrying it very well could be another issue, and once you remove that screw for the optical sensor and move it, it's difficult and time-consuming to find the perfect positioning.

Thanks.

 

[bibilit]

I have had some issues while testing drives, when the drive was too close from the CRT, and having the same behavior. 

Not saying this is the problem, but from that day I avoid the method. 

 

[JDW]

Are you saying that when you moved your 800K drive outside the Mac the heads move all the way back and then stopped?  And then when you put the drive back inside the Mac the head moved normally again?

I must say that I've not heard that before.  Hmmm...

 

[bibilit]

Yes, the magnetic field of the CRT is known for having this kind of nuisance. 

Inside, the drive is protected by the bracket in normal use, but hanging the drive the way i see it on the video can be the problem. 

 

[LaPorta]

He wrote the same to me on my channel. I never have seen this behavior before, either. It sounded to me more like an electronics fault issue. 

 

[bibilit]

See above, seen that with 400k drives and 800k as well. 

Again, not saying is your problem, just advising that I have seen that several times. 

I use an external drive loom for testing purposes. 

 

[JDW]

Actually, @bibilit, I am even more confused after having read through that other thread, mainly because it says this in the opening post...
 

when I take out the floppy drive from the mac it works perfectly and inside it does sometimes

Reading the above text at face value, I interpret it to say, "Drive operation is intermittent when the drive is inside the Mac, but upon removing the drive and placing it outside the Mac and testing it, the drive works perfectly."

Now let's consider the case I am speaking of in this thread.  The drive did not work perfectly while inside the Mac, prompting the user to remove it and lube it.  But even after the lube job, what you see in the videos that I posted earlier remains.  And of course, those videos show the drive OUTSIDE the Mac, which is the inverse opposite of what that other thread is saying.  

I can of course have this gentleman place the drive inside it's metal mount and then have him alligator clip that mount to chassis ground, but I suspect that will do nothing at all.  Interference from the CRT might cause intermittent operation or even bad reads and writes, but I cannot see how it would cause a consistent and recurring problem of the head moving all the way back to Track 0 every single time it is powered, nor does it explain why the head moves all the way back when you move the head forward manually with your finger.  So I do not think shielding and grounding will do any good.  Indeed, since there are no other guesses as to what is wrong, my initial guess about the Track 0 optical sensor being misaligned is probably correct.  Even so, I posted here because the gentleman in question is concerned it might be some other problem. I just didn't know what other problem it could be.

 

[CC_333]

I have a pile of drives that do this (regardless of where/how they're installed), and it's driving me crazy because I don't have many other working spares!

I don't have anything useful to add (aside from another test sample, I suppose), but I nevertheless will be following this thread intently to see if anyone can discover a solution I can try!

c

 

[JDW]

I have a pile of drives that do this (regardless of where/how they're installed), and it's driving me crazy because I don't have many other working spares!

I don't have anything useful to add (aside from another test sample, I suppose), but I nevertheless will be following this thread intently to see if anyone can discover a solution I can try!

The following is the advice I offered to the individual who commented on my YouTube Channel (Track Zero Alignment):

https://bit.ly/3cnyKbr

https://bit.ly/3tczCGa



Search this PDF for "Verify the disk drive's general operating" to jump to the right section: https://vintageapple.org/macbooks/pdf/The_Dead_Mac_Scrolls_1992.pdf




 


Please let me know if this helps.

 

[CC_333]

The following is the advice I offered to the individual who commented on my YouTube Channel (Track Zero Alignment):

...

Please let me know if this helps.

Will do!

c