pin 28 on ribbon cable, you can just cut it permanently pulling it high

rasz_pl wrote on 2023-10-03, 14:25:

pin 28 on ribbon cable, you can just cut it permanently pulling it high

I don't think this will work on all drives. While it prevents the FDC from detecting that the disk is write protected, the drive still may ignore the write gate line if a write protected disk is inserted. I used to think that most drives handle write protection internally, and pin 28 is just to inform the controller that writing will be futile, but I'm not sure about this.

mkarcher wrote on 2023-10-03, 15:32:

rasz_pl wrote on 2023-10-03, 14:25:

pin 28 on ribbon cable, you can just cut it permanently pulling it high

I don't think this will work on all drives. While it prevents the FDC from detecting that the disk is write protected, the drive still may ignore the write gate line if a write protected disk is inserted. I used to think that most drives handle write protection internally, and pin 28 is just to inform the controller that writing will be futile, but I'm not sure about this.

Correct. The write protection is implemented in the drives' hardware for a properly built drive, the line in the data cable is only to inform the host

if you have a multimeter you can measure voltage on the components (sensor/led) on both sides and see which one changes when a write protected disc is inserted.
Then it becomes a matter of overriding that change so the floppy hardware sees the disc as writeable.

That looks like it's a high density drive; why is flipping/notching disks a consideration?
Or are you talking about writing to software disks that were made without the notch even on the "right" side of the disk

weedeewee wrote on 2023-10-03, 15:47:

if you have a multimeter you can measure voltage on the components (sensor/led) on both sides and see which one changes when a write protected disc is inserted.
Then it becomes a matter of overriding that change so the floppy hardware sees the disc as writeable.

That's a great idea! Thank you very much, I appreciate it.

jakethompson1 wrote on 2023-10-03, 15:51:

That looks like it's a high density drive; why is flipping/notching disks a consideration?
Or are you talking about writing to software disks that were made without the notch even on the "right" side of the disk

That's correct, attempt at repair for a few disks that I don't want to notch, would be nice if I can bypass it on a hardware level 😀

Interesting idea ! The only disks I know without the notch are mostly from specific software groups which had mostly 360k DD w/o the notch so you did not mess with the original disks. But that brings up a diff question as to why you want to do it ? 🤣

Horun wrote on 2023-10-04, 03:19:

Interesting idea ! The only disks I know without the notch are mostly from specific software groups which had mostly 360k DD w/o the notch so you did not mess with the original disks. But that brings up a diff question as to why you want to do it ? 🤣

I have a few original disks with bad sectors that also have quite a fair few unused good sectors so I am trying to repair the disks essentially. It's a long shot and may not work but I'd like to still keep the integrity of the disk without cutting it 😀

On TEACs the upper part is the sensor, lower is IR LED. Usually the sensor will present high impedance that drops low when it is illuminated by the LED. To create a write enabling bypass you'd short the sensor (preferably via a resistor and not just a wire, try 100 ohms first).

EDIT: You want to have a switch for that though. TEACs do not have a separate media present sensor, floppy insertion/removal is done via the WP sensor as well. The drive might not operate properly if the sensor is never occluded. I never actually tested this though so you can try without a switch first. One thing that will not happen is the motor will not turn on for a moment when the floppy is inserted, this helps to center it better so you might sometimes end up with poor media vs spindle aligment. That will affect how well the head follows the track. It's not super critical but you need to know that if you want to read, or "refresh" the floppies - if you end up with a rewritten floppy that doesn't work well on other drives you might need to repeat the writing process, or even do some media erasing with a magnet first.

Deunan wrote on 2023-10-05, 13:18:

On TEACs the upper part is the sensor, lower is IR LED. Usually the sensor will present high impedance that drops low when it is illuminated by the LED. To create a write enabling bypass you'd short the sensor (preferably via a resistor and not just a wire, try 100 ohms first).

EDIT: You want to have a switch for that though. TEACs do not have a separate media present sensor, floppy insertion/removal is done via the WP sensor as well. The drive might not operate properly if the sensor is never occluded. I never actually tested this though so you can try without a switch first. One thing that will not happen is the motor will not turn on for a moment when the floppy is inserted, this helps to center it better so you might sometimes end up with poor media vs spindle aligment. That will affect how well the head follows the track. It's not super critical but you need to know that if you want to read, or "refresh" the floppies - if you end up with a rewritten floppy that doesn't work well on other drives you might need to repeat the writing process, or even do some media erasing with a magnet first.

This is fantastic information. Thank you very much!
Didn't even consider alignment issues.

Did you ever do this modification? how did it go?