Sony MP-F75W-01G oscilloscope debugging

[DaveW]

So, I might have buggered my floppy drive in my Color Classic. I got the system at auction a little while ago and to start it would boot fine from the HDD but not read floppies. I took the back cover off and blew out the crap in the case and in the floppy, and after that I was able to load some disks and install software though it was a little intermittent. I then decided to properly clean and lube the floppy, but moved the ZTS while I did. When I got it back together, it wouldn't read or format anything.

Disassembled the drive again and I noticed the heads were separated with a disk inserted, so I adjusted the spring to close them. I'm not sure if that's a result of my cleaning the heads with a q-tip and iso or just sitting for years with no disk. Still no luck, so I've been fiddling with the ZTS. Using paolo's dot technique I've tried each step from all the way back to all the way forward with no success.

I've seen many posts suggesting these debugging methods are the best you can do without an oscilloscope, but I haven't seen anything about debugging a drive with a scope. I have a pretty fully stocked electronics lab, so I'd like to take a crack at getting this drive up and running. I don't have a working spare to compare with, but does anyone have a guide to aligning heads and the ZTS with a scope? I have a schematic and don't mind soldering some test leads on it and messing around, but I'm not sure what kind of waveforms from the heads or triggers I should be looking for.

Thanks

 

[cj_reha]

When you say the heads were "separated with a disk inserted," do you mean that the top head is not coming down to the disk surface? Out of curiosity, when cleaning the heads, did you lift the top head to clean it?

 

[LaPorta]

Yes, when cleaning heads, the most you ever want to do is keep the drive in the up position, and stick a q-tip with IPA in between them and sweep back and forth. That's it. Don't move the head up.

 

[DaveW]

When you say the heads were "separated with a disk inserted," do you mean that the top head is not coming down to the disk surface? Out of curiosity, when cleaning the heads, did you lift the top head to clean it?

Correct, with a disk inserted after cleaning the top head didn't come down to the disk surface. I wasn't really paying attention to the head separation while cleaning it, though I don't remember opening it further than the centimeter or so it's separated in the no-disk open position.

This is what the top and bottom head surface looks like, and what they look like together.
The heads themselves look pretty well aligned, but the notches between the read heads aren't perfectly aligned. I have no comparison for what the alignment looks like on a new drive.

 

[DaveW]

So, I got it working. I disassembled a Sony internal PC 1.44MB floppy to check, and it has the same center notches and they were lined up quite well. I was actually thinking I might just do a head swap, but the distance between the slide rail and stepper screw was greater in the PC drive.

So, I unhooked the tensioning screw and pulled the top head off. Both the bar in bottom head and the leaf spring retaining bar on the top head are threaded so I drilled out the threading on the top head retainer, and used a knife to remove the bit of a glue ridge where the top head leaf sits on the bottom so I could adjust it. I flattened the top head leaf in a vice, then reassembled it and snugged the screws without fully tightening them. I then just visually aligned the center notches in the head, tightened it back up, and gave it a test.

Didn't read at first pass, but I could successfully format and mount which is more than it was able to do before. Adjusted the ZTS and now it reads and writes disks fine.

I am guessing that when bending the head back down do it would touch the disk I pulled the heads out of alignment and that caused the issue. Thankfully fixed.


I would still be interested in knowing so test points and expected waveforms for these floppy drives for debugging in the future if anyone has them though.