Sony 920 MPF z/121 fix for Amiga

[prowler]

Originally Posted by Techseeker

Found a little more info here, might be related

http://eab.abime.net/showpost.php?p=538186&postcount=77

Looks like that rats nest started life as a TEAC FD-235HF mod, then sony.

It would be interesting to see if it works.

Hmm... It seems that the original thread on a1k.org no longer exists. That's a pity, but thanks for the link nonetheless, Techseeker!

[kipper2k]

There are so many board revisions of the Teac, its hard to keep track of them all, the earlier boards had jumpers which were later abandoned and then it looks like at the end of the Teac revisions they became uncompatible.

[kipper2k]

Heres pic of the Teac as promised...




click on link to view Hires image and see the connections and info.

http://www.kipper2k.com/amiga/teac.jpg

[kipper2k]

Here is the fix for the Panasonic 198pc floppy.




heres the link for the hires pic...

http://www.kipper2k.com/amiga/198pchires.jpg

[rkauer]

Originally Posted by prowler

Now, in view of Techseeker's affirmation that this replacement unit is, in fact, a converted HD floppy drive, I'm going to have a look inside the two Power Computing XL (High Density, 1.76MB) Amiga external drives that I also have, to see whether they are similarly converted drives.

If they are, it will mean that this drive will also read Amiga 1.76MB High Density floppies if it is fitted in one of those devices and with the Power Computing Workbench patch installed!

I use to have one of those Power Computing HD external drives. It dies on my hands, the little GAL chip bit the bullet.

The unit itself is just an unmodified pc-style Sony MPF920 drive, all the conversion and logic is done by the little logic circuit, which is impossible to read.

[prowler]

Thanks for the info, rkauer. So it looks like the MPF920 I have is a replacement for the Power Computing XL Drive internal floppy drive mechanism.

I haven't had time to do so yet, but I will open up my two XL Drives later and check to see what they have in them.

[prowler]

Okay, I've opened up both my Power Computing XL Drives.

One has an Issue F HDDRIVE interface; the other an Issue G. However, both models have a Sony MPF520-1 1/130 floppy drive mechanism.

I will dismantle the internal drive mechanisms tomorrow when I can clear a space (I opened up the drives this evening on the landing window sill ). I will, of course, upload some scans if I find any interesting modifications.

[rkauer]

Again: the drives themselves have no modification at all: ordinary PC drives. All "magic" is done by the power XL circuit.

[prowler]

Originally Posted by rkauer

Again: the drives themselves have no modification at all: ordinary PC drives. All "magic" is done by the power XL circuit.

I'm sorry, I misread your earlier post. I had thought that the "little GAL chip" you referred to was similar to the one used to modify my MPF920 drive.

I must admit that there is a good deal more circuitry on the Power Computing HDDRIVE interfaces than on other external drive interfaces I have seen.

I have not stripped those drive mechanisms yet. If what you say above is true then it seems that they will turn out to contain no modifications at all. In that event, I will post scans of the HDDRIVE Issue F and G interfaces instead.

[rkauer]

My friend, beside the "magic" HD tricks all the Power XL drive do is commonly available at Aminet: they simply swap the 2 & 34 pins and provide the "true" ready signal.

[prowler]

Originally Posted by rkauer

Again: the drives themselves have no modification at all: ordinary PC drives. All "magic" is done by the power XL circuit.

This evening, I have stripped both my Power Computing XL Drive internal drive mechanisms and I can confirm that both contain no modifications at all.

As promised, here are scans of the HDDRIVE Issue F and G interfaces, respectively:

Originally Posted by rkauer

My friend, beside the "magic" HD tricks all the Power XL drive do is commonly available at Aminet: they simply swap the 2 & 34 pins and provide the "true" ready signal.

So, it seems that the Power Computing XL Drive interface can also be used to connect a PC floppy drive mechanism, irrespective of density, to an Amiga as an external floppy drive, and that has given me an idea...

[jmmijo]

I bet the respective PAL/GAL chips on each drive interface probably do the magic trick of converting the PC floppy drive into an Amiga floppy drive

[prowler]

Originally Posted by jmmijo

I bet the respective PAL/GAL chips on each drive interface probably do the magic trick of converting the PC floppy drive into an Amiga floppy drive

No. All you need for that, as rkauer notes above, is to swap pins 2 & 34 and provide the "true" ready signal. This is achieved on regular external drives without the HD feature.

The GAL chip does the "magic" of halving the disk rotation speed when reading/writing high density disks, to keep the data rate compatible with that for double density disks.

[Techseeker]

Is that a memory chip I see too, maybe some type of buffer to compensate for the difference in rotation ? Maybe the floppy doesnt drop to 150RPM?

[prowler]

Originally Posted by Techseeker

Is that a memory chip I see too, maybe some type of buffer to compensate for the difference in rotation ? Maybe the floppy doesnt drop to 150RPM?

Yes, it's a 128K RAM chip (4x256K configuration), but I'm not sure how it could compensate on a continuous basis for insufficient reduction in rate of rotation. It's more likely that it is used to compensate for the effect of slight fluctuations.

[Techseeker]

I dont know either, I nearly typed that first, but if the floppy isnt modified, then in HD mode is it still doing 300rpm like it would in a PC?

[prowler]

Originally Posted by Techseeker

I dont know either, I nearly typed that first, but if the floppy isnt modified, then in HD mode is it still doing 300rpm like it would in a PC?

A true Amiga high density drive, as you know, drops to 150RPM rotation speed when using HD formatted disks, to match the data transfer rate when the disks are DD formatted.

Such a high density drive will operate in this manner without extra hardware or patches to the operating system.

The Power Computing XL Drive requires a patch to the operating system in order to be able to write high density formats. However, it can read any format, either high or low density, without the patch installed.

I imagine that, to be able to achieve this, the XL Drive must mimic exactly the features of a true Amiga high density drive, in particular the lower rotation speed.

However, PC drives it uses are not designed with performance at 150RPM in mind; hence the need for buffering to overcome the possibility of speed fluctuations due to "hunting".

[prowler]

@Techseeker/rkauer,

This is the modified Sony MPF920 floppy drive I described earlier in this thread:



In your opinion, would this unit operate as a true Amiga HD floppy drive in my KS3.1/WB3.1 A1200 without further modification?

If you're not sure, I think I might try it anyway.

Originally Posted by fitzsteve

Thats the drive that came in a Power Tower I bought on ebay, I took out all the bits I needed like the Mediator, Voodoo, Blizzard. Since I already had a brand new Amigakit FDD it was surplus.

So it's not inconceivable that it might have been converted to operate as an Amiga HD floppy drive, then, is it?

[Techseeker]

Yep, I am agreeing with you. This should work as in HD as DF0:

Give it a shot and let us know

[prowler]

Originally Posted by prowler

This evening, I have stripped both my Power Computing XL Drive internal drive mechanisms and I can confirm that both contain no modifications at all.

So, it seems that the Power Computing XL Drive interface can also be used to connect a PC floppy drive mechanism, irrespective of density, to an Amiga as an external floppy drive, and that has given me an idea...

This evening, I attached a Mitsumi D359T5 high density PC floppy drive to the HDDRIVE interface of one of my Power Computing XL Drives and connected it to the external floppy drive port of my Commodore A1200 as DF1:

The Amiga would not read any Amiga formatted disk I inserted in the drive, displaying DF1:????, PC1:???? and MAC1:???? icons on the desktop.

However, the Mitsumi D395T5 drive works flawlessly when attached to the internal floppy drive port via Stedy's PC floppy drive adapter.

My hope that the Power Computing XL Drive interface could be used to connect any PC floppy drive mechanism to an Amiga as an external floppy drive is thereby dashed.

Originally Posted by Techseeker

Yep, I am agreeing with you. This should work as in HD as DF0:

Give it a shot and let us know

Thanks, mate! I'll give it a try tomorrow. I'm hoping for better luck with that.