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Issues with 800K drive motor control

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andrew:
I've been having an issue for a while with 800K drives connected to my Lisa. I thought that perhaps it was related to the existing 400K ROM, but I recently finally got around to researching and getting all the materials I needed to burn a universal drive rom (yes, I know it's been a year  :-[). I can confirm I burned the ROM correctly because I was able to get one of the drives to write 800K to a disk that reads correctly in my Mac Plus.

The main issue is the drives will run their ejection mechanisms constantly. One drive repeatedly tries to eject while the other constantly tries to intake a disk, such that to eject or insert a disk I need to manually hold down the drive ejection switch. Both drives work on my Mac Plus without issue, but when connected to the Lisa they malfunction as such.

Has anyone else had this problem? What was the underlying issue?

sigma7:

--- Quote from: andrew on February 17, 2024, 07:15:52 pm ---800K drives ... run their ejection mechanisms constantly

--- End quote ---

Apple changed the 800k drive version at some point, and this was the symptom if the newer version was put into one of the earlier Macs.

I think the version change may have corresponded to removal of the "auto-inject" feature of the earlier drives, where the earlier drives would sort of finish the insertion of a disk for you with a snap action, while the later version required that you keep pressing the disk in until it dropped down with a more manual feel like the 400k drives. (Or maybe I've got that backwards.)

The newer drives (or some at least) used a ribbon cable with a yellow stripe instead of a red one. Those cables are missing conductors in the 9th and 20th positions. That isn't evident unless you look at the end of the ribbon where you can see those are solid plastic whereas the others contain obvious metal strands.

So disabling the constant eject requires disconnecting one or both of those. (Perhaps someone else knows if both need to be cut?)

Since you probably don't want to modify your Lisa's cabling (so you can use a 400k drive in the future), you might purchase/make an extension or something similar.

eg. cut wires 9 & 20 of DigiKey part# H3AWH-3006G

edit: added some details, DigiKey part#, corrected some errors and made new ones

ried:
That is an excellent explanation and I concur. Ran into the same issue with my Macintosh 128K, and changing the floppy drive cable fixed it. I did not know it would affect a Lisa in the same way.

andrew:
It's an incredible relief to know there's a simple explanation for this. Rather than cutting wires on that digikey part, I'll just find a yellow stripe cable on ebay and swap it with the red stripe cable I'm using between my floppy A/B switch and the drive cage cable. Hopefully this will fix the issue.

AlexTheCat123:
Ohhhhh! I had always wondered why one of my Lisas with an 800K floppy upgrade had a label on top of the floppy drive that said that "this 800K drive must be used with the cable that was included with the drive" but I guess that explains it! I thought it was really strange that you couldn't just use the existing 400K drive cable, but this makes a lot of sense if Sun switched over to using the manual inject drives at some point.

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