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Can't figure out 360K floppy drive

twolazy said:
If the speed is right, you will see one of the dotted lines seem to almost stand still. Never had to do this to a floppy drive, but have with many turntables.
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Ok, so I tried a new app called Strobe RPM Tachometer Lite, and discarded the pattern, replacing it with just a single rectangle. Can someone else download the app and use it on something they know is a specific RPM to see if the app really works? Because, according to the app, it would appear that the drive is running at 330rpm. Is that within spec? Or would anyone also happen to know which pot to turn to fix that. There are only two on the top, and the one labeled VR2 appears to be secured so it can't be moved. And can it be adjusted while the drive is running, or should I turn it off first and do some trial and error?

mc-20230525_175738.jpg
 
That's what I meant. One of those circular patterns should appear stationary while the other 2 won't.
 
Image Disk can check RPM. But you'd have to have a drive that is somewhat working I would think. Would you be able to run this off of the hard disk? I don't remember what type of system this is for. Can you get to DOS of some form?
 
IMD relies on a readable sector (check the source code) to calculate RPM.

With a 'scope or other timer, the INDEX/ pulse can be sampled to get a value that doesn't depend on a disk having anything readable.
 
Ah, I figured it was something like that. Did not know how it did it. Thanks Chuck.
 
That's one of the differences re the NEC µPD765 family and the WD 17xx family. The NEC chip "hides" the index pulse from direct program observation, while the WD chips even provide an interrupt for it. So the PC-type FDCs have to work around it.
 
Does anyone know if there's a DOS/Win98 equivalent to Speed Test by Zibri? Or is a piece of software like that not even possible for IBM style machines because of the differences in hardware?

I think this would be a lot easier if I had a piece of software that told me the RPM regardless of outside factors.

Also, looking at the 1541 as a very very rough cross reference, I think the pot VR2 is the one that governs the speed of the spindle motor because it has the same blue glue stuff as the pot on the 1541.

Is that assumption fair?
 
I decided to take a video to show you guys the speed. I ran the app at double the speed so it would be easier to see on camera, so the RPM according to the app is doubled.

View attachment 1_20230608_190421.mp4

In the video, I started at 600rpm (300rpm), and then switched to 660rpm (330rpm).

While not perfect, it's clear that the drive is running closer to 330rpm than 300rpm, yeah?
 
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This makes sense. Adjust the pot/screw while the drive is running until it's as close to 300rpm as you can get. Err on the side of slower if you can't get it exactly 300 rpm.
 
No matter what pot I turn, the spindle motor will not speed up or slow down. VR2 appears to control something to do with the head stepper motor, as it gets loud or quiet depending on what position the pot is in. As far as I can tell, it doesn't effect the functionality of the drive. VR1 controls how the data is read in some way, but it doesn't affect the speed whatsoever. moving it to the far left or right makes ImageDisk unable to read the data, and tweaking it in between makes it bounce between 2-4 sectors detected. The speed always stays between 330-335rpm no matter what I do.

In addition, no amount of tweaking the two pots makes a correctly formatted disk readable. It's always just "?" no matter what.

This is all very aggravating.

Now I've turned the only two pots and I have no idea what they really even do 🤦‍♂️
 
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Ah, this is how the fun starts. Turn pots you don't know what they control. Been there, done that. I would have thought one of them would have been for the spindle motor. Somehow we'll get to the bottom of this and figure out what to do. But I am not that smart.
 
I wonder if this would be a good use case for one of those $30 oscilloscope you can get on eBay, from China.
 
Was it common to use feedback to lock rpm? I wonder if somehow the feedback loop is open, and the drive is spinning uncontrolled at a max railed value.

The drive looks to me like the drive is not stably running at 330 rpm.
 
Another thought. If the feedback loop is closed by the wiper on the pot, then it would be possible that the pot wiper has failed open, breaking the feedback loop.

Wiper current must be really low to avoid problems over time.

Anyhow a quick check would be to twiddle the pot while monitoring the voltage on the wiper. If you see the voltage adjusting, the wiper is making contact and probably is ok.
 
Twospruces said:
Was it common to use feedback to lock rpm? I wonder if somehow the feedback loop is open, and the drive is spinning uncontrolled at a max railed value.

The drive looks to me like the drive is not stably running at 330 rpm.
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Do you know how I could check for that? The only tool I have is my multi-meter at the moment.

Twospruces said:
Another thought. If the feedback loop is closed by the wiper on the pot, then it would be possible that the pot wiper has failed open, breaking the feedback loop.

Wiper current must be really low to avoid problems over time.

Anyhow a quick check would be to twiddle the pot while monitoring the voltage on the wiper. If you see the voltage adjusting, the wiper is making contact and probably is ok.
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It seems like the pots are ok. I removed the board from the drive and tested them using my multi-meter. They both display an output and changed when the pot is adjusted. I included a picture of the back of the board.

20230609_170526(1).jpg

VR1 is above and VR2 is below

Side note: does anyone know what the numbers in ImageDisk Alignment test mean? I tried checking the manual and couldn't figure it out. I know that the first number is the sector number, but I don't know what the second and third numbers are. The second number seems to go up the closer to the middle VR1 gets, and then gets gradually lower the further it gets from the center before the disk becomes unreadable. Does it have something to do with stability? And, the third number seems to always stay at 0.
 
I'm not aware that there even is a way to adjust the speed on these drive. I'd expect such a control to be on the motor board, but there is nothing.

I'm still a little suspicious that that even is the problem. Can you get the NFORMAT disk formatter on your system? If you can, try setting the sectors per track to 4 sectors (yes, that will normally work) and see what happens. If that works, increase the number back toward 9 and see if/when it fails.
 
SomeGuy said:
I'm not aware that there even is a way to adjust the speed on these drive. I'd expect such a control to be on the motor board, but there is nothing.

I'm still a little suspicious that that even is the problem. Can you get the NFORMAT disk formatter on your system? If you can, try setting the sectors per track to 4 sectors (yes, that will normally work) and see what happens. If that works, increase the number back toward 9 and see if/when it fails.
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Using a completely fresh DSDD diskette, I get this error:

20230609_181154(1).jpg20230609_181210(1).jpg

It appears to check sector 1 on head 0 before instantly failing.
 
Well, at this point, I wouldn't touch the drive without a 'scope. Since this is a 5.25" drive, the failure doesn't seem to be related to the position of the spindle, as the failure seems to result in the only the last 4 sectors on the track being readable.
 
That first photo still says "sectors: 9". At the menu, highlight "360k", edit the parameters, and change Sectors On Track to 4.
 
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