1541-ii head problem

[Gyro Gearloose]

The 1541-ii I bought "as-is" a while ago powers up and responds to commands but doesn't read any disks.
Turns out the head is open circuit.
Besides attempting surgery to remove the epoxy in the head under a microscope, is there a supply of spare heads somewhere?

[Gyro Gearloose]

Oooooh, turns out the "epoxy" is more like a jelly. Very strange!

[eslapion]

viewtopic.php?f=12&t=9415&start=10

[Gyro Gearloose]

Hmm, thanks. The Tektronix P6042 DC-50MHz current probe has the same type of flaw. But they used very hard potting and it failed too. But that failure was the core itself breaking where Tektronix embedded a Hall sensor in the core.
Those windings were made with 39AWG wire, I know pretty well how this kind of stuff is hard to handle.
Indeed my mechanism is a Mitsumi Newtronics D500.
At least I can't do more harm by soaking the head potting in a bit of "Super Remover" paint, varnish, and glue remover. If that doesn't work I'll use what they euphemistically call "over-curing", ie, lots of heat.

[Gyro Gearloose]

Going to try with the hot air station at work, there's a good microscope there too.

[Gyro Gearloose]

Too busy at work. Besides I want to try a hot wire cutter made of nichrome to scoop out the goo.

[rmzalbar]

It's possible to peel the coils out of the goo if you're careful. I'd be curious to know where the coil failed - before you tear it apart, check the resistance between the various wires. On mine the failure was between the r/w coil (red) to its center tap (white). Check white-to-red and white-to-blue.

Page 18 of this document has the continuity checks, wire colors, and schematic. Mind there is a resistor in there, so the coil won't read "open circuit" but the resistance will be too high.
https://www.classic-computing.org/wp-co ... MANUAL.pdf

[Gyro Gearloose]

I used the "overcure" technique. That's fancy-talk for jamming in a soldering iron tip set high. It burns the material and it crumbles away.
I'm still trying to find a data sheet or drawing of what a head looks like, what it's made of, the potting compound, the head material, the polishing smoothness or whatever.
I'm googling patents too. It's a bit of work but slowly I'm getting a picture of what is involved in making a head.

[Gyro Gearloose]

I bought a used Chinon drive on eBay to repair this drive but it's in rough shape. The eject shaft has been cut off and the head, while measuring correct, has a scratch in it that might make it unusable.
I think I'll stick to 1581s from now on.

[Gyro Gearloose]

I managed to get a handbook that talks more about floppy drive heads and the manufacturing of discs as well. There is a whole lot of engineering involved here, not just the electrical engineering of how to generate a pulse... Building a floppy drive head, even early '80s technology, is a significant challenge in materials and precision manufacturing.
Not easy at all.
This is probably why the few companies left that still make mag heads for stripe readers all said "noooooope" when I asked about floppy heads.
At the very least they would need to see some $$$.
Audio folks don't seem interested either, I suppose because the materials aren't the same at all.