Will the MP-F51W-23 Work Inside the Macintosh 512Ke (As Opposed to the MP-F51W-03)?

[SilverStreaks]

I have a Macintosh 512Ke and recently the disk drive (MP-F51W-03) failed. Unfortunately I'm unable to find any replacements online, but I am finding drives with model no. MP-F51W-23, which seem to be the part used in the 800K external drives. Can I expect this to work if I plug it into the internal floppy port of my mac?

 

[volvo242gt]

Yup. You might have to switch to a red stripe floppy drive cable, since some 512ke & Plus machines used a yellow stripe cable. If you use the red stripe cable, you can even use a MP-F75W in there. It just won't read HD disks, only doing 400K and 800K disks.

 

[SilverStreaks]

Yup. You might have to switch to a red stripe floppy drive cable, since some 512ke & Plus machines used a yellow stripe cable. If you use the red stripe cable, you can even use a MP-F75W in there. It just won't read HD disks, only doing 400K and 800K disks.

Awesome. Is there somewhere that lists out all the drives that are compatible? Also, will they fit into the existing 800K drive cage?

 

[volvo242gt]

Both drive series are the same form factor, so they will fit the Plus-style bracket. I'd get in touch with Herb Johnson to get the full listing of drives, but any Sony drive that starts out with either MP-F51W or MP-F75W (or MFD-51-W or MFD-75-W) is compatible with a 512Ke or Plus. On the MP-F51W drives, the ones with a red MFD-51-W label on the side use the yellow stripe cable. The ones with the black MFD-51-W or a 51W-IO label on the side use the more common red stripe cable. Sounds like you'll need the red stripe cable, which is 590-0167, instead of the yellow stripe cable installed on your 512Ke.

Here's Herb's notes when it comes to the various cables.

http://www.retrotechnology.com/herbs_stuff/mac_800k_cables.txt

 

[bigmessowires]

My undying gratitude to anybody who can clearly and definitively explain all this red stripe / yellow stripe business. I've been in this hobby for a while and I've even built a business around Macintosh floppy drive knowledge, and I still don't understand it. I know you need to use the right cable with the right drive. I know it has something to do with the PWM speed control and the disk eject. And I know that using the wrong cable can make the drive eject the disk over and over forever. But I would love to see more detail about the exact pinout/signal differences in the different floppy drive versions, the pinout/signal differences on the Mac motherboards (if any), and how the red/yellow cables resolve the problem.

 

[Chopsticks]

It’s likely due to pin 9 originally being used to provide -12v during the Apple II days but during mac development for whatever reason they choose to no longer connect that pin on the logic board. In fact I think latter floppy drives themselves had that pin connected to +5v.

So I probably wouldn’t just go plugging a newer drive in using the wrong cable, it might end up shorting +5v to -12v. I’m not sure if that’s really safe, it could potentially backfeed around a 7v rail everywhere on the 5v rail.
If you have a second cable just cut pin 9 if you use a newer drive.

As for pin 20, while I’m not certain of this, but I think early mac drives had the disc controller send the pwm speed signal to the floppy drive, those original Apple DiskII drives were ‘dumb’ electronics internally

At some stage early on the drives in macs also changed to provide that PWM signal on the drive electronics itself (probs in the 400k to 800k transition).

 

[bigmessowires]

You're correct about pin 20. But as far as I know, there's no harm in supplying the PWM signal to newer 3.5 drives that don't need it.

A couple of years ago I wrote a long blog post titled "Pin 9 Is Not My Friend", where I looked at 20+ different 3.5 and 5.25 inch drive mechanisms to see how they used pin 9. https://www.bigmessowires.com/2021/08/13/floppy-drive-pin-9-is-not-my-friend/

 

[Chopsticks]

@bigmessowires im pretty sure my info above came from reading your blog posts on a Apple disk controller you were working on at some stage. Considering it was a few years ago Im glad I at least remembered half correctly.


After looking at your link above, which is great info too btw, I’m pretty sure it was the Yellowstone card you mention that I’m also remembering reading on your blogs.

 

[volvo242gt]

@bigmessowires If you install a bare MP-F75W or black label F51W drive into a PCI PowerMac, it will continually eject, just like what's described when using a red stripe cable with a red label F51W drive. I tried that in the summer of 2003 with my old PowerMac 7500/100. Wanted the nicer auto-inject F75W mechanism in the 7500. Alas, it just kept running the eject motor. So, I'm thinking that pin 9 on those mechanisms may be connected to the external eject switch on the A9M0106 and G7287 drives. I seem to remember that A+ magazine said in their floppy drive article from early 1987, the A9M0104 and disk ][ drives weren't fully compatible with the IIgs's smartport. The A9M0104, of course, can easily be modified to work. Either cut pin 9 on the analog board, or swap in the analog board from an Apple 5.25 Drive (A9M0107).

 

[bigmessowires]

I should update the table in my blog post with the part numbers of the various internal drives. MP-F51W, MP-F51W-03, MP-F51W-23, MFD-51-W, 51W-I0, MP-F75W, MFD-75-W, any others? There are more different part numbers than there are types of internal 3.5 inch floppy drives I know of. Unfortunately I didn't write down those numbers when doing my pin 9 testing and creating the table of drive behaviors, I just called them "bare 800K 3.5 drive, black label" and similar. Do you know of any comprehensive list of model numbers?

There's one thing bothering me about all of this: if my understanding and my drive table is halfway correct, then none of the 3.5 inch floppy drive mechanisms actually require any voltage or signal on pin 9 (some can tolerate an input voltage on pin 9, some can't). So the yellow stripe cable (pin 9 and 20 internally disconnected) should work for any computer, any floppy drive, with the exception of 400K drives which need pin 20. Is that actually true? If so, why didn't Apple use the yellow stripe cable everywhere? Why do we even have red stripe cables at all? Is it a cost-cutting thing, since straight-through cables are easier to make?

And for that matter, instead of solving this pin 9 problem with special cables, why didn't Apple make pin 9 be a "no connection" on every Macintosh motherboard? Then we could have used regular red stripe cables everywhere. I feel like there's something important that I'm not understanding.

 

[pl212]

Awesome. Is there somewhere that lists out all the drives that are compatible? Also, will they fit into the existing 800K drive cage?

My undying gratitude to anybody who can clearly and definitively explain all this red stripe / yellow stripe business.

I came across this table in a 1990 service guide -- at least for me, it helped clarify things.

Having said that, I think there is a contraction between the un-enhanced 512K only working with a 400K drive (in the chart) and footnote 2, which states that a yellow cable will make an 800K drive work in that machine. (My understanding is that an un-enhanced 512K should work with an 800k drive, either using MFS or -- if you boot from the HD20 floppy disk -- HFS.)

 

[volvo242gt]

Interesting, since every SE, SE/30, etc, I see, came with a red stripe cable, if it uses a FDHD drive, or a later black label 800K drive.