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Choosing between three Sony MPF-920 drives

Posted: Wed Sep 20, 2017 10:58 pm
by Pacman
In the process of reviving one of my two Ataris I realized that one of the two floppy disk drives (a Sony MPF-920 "E" model (dated February 2001 and with a Sony IC) no longer worked. The other drive (an older drive -a Sony MPF-520) works fine in both machines, also in HD mode in the Mega STe which is where I'll put that drive back in when I'm done repairing the computer.

So I need a replacement drive for my STe and have just been offered one of three Sony MPF-920 drives from a PC user who doesn't need them. The question is which of the three I should get. He kindly provided some photos:
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An MPF-920-Z/1M1 from November 2004.

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A Z/121 version of the MPF-920, dated April 2009.

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Finally another Z/1M1 version of the MPF-920, also dated November 2004 like the first one

He had a look inside one of the Z/1M1 drives (doesn't know which one) and was pretty sure he could see a BH-955 chip on its PCB. He didn't open up the Z/121 version though.

Exxos has plenty of info on these Sony MPF-920 drives here and in what I believe is a compressed version with the same information in this forum thread, where his experience is that certain models/date periods have resulted in unusable drives (at least for use with the ST).
There's no mention of the Z/1M1 version, but he assumes that any of these drives produced from 2004 and onwards should be OK.
I assume the Z/121 version above, from April 2009 would be the best choice then, being the newest one (which in turn probably means it's the least used one as well). Any views on this?

I've also received (and completed building) Exxos' 1.44MB HD module which I intend to put inside my STe once I get a drive working, allowing me to use the drive in both DD and HD modes.

Re: Choosing between three Sony MPF-920 drives

Posted: Thu Sep 21, 2017 12:16 am
by exxos
I would go with the later 2009 drive.

Re: Choosing between three Sony MPF-920 drives

Posted: Thu Sep 21, 2017 5:51 am
by Pacman
Thanks. Based on your previous experience I should probably be fine, unlike with the 920-E (2001) "lemon" I had from before.

Re: Choosing between three Sony MPF-920 drives

Posted: Thu Sep 21, 2017 8:10 am
by exxos
If you can confirm its using a BH chip then I will add it to my list.

Re: Choosing between three Sony MPF-920 drives

Posted: Thu Sep 21, 2017 8:29 am
by Pacman
No problem.
I'll post back when I receive it.

Re: Choosing between three Sony MPF-920 drives

Posted: Mon Sep 25, 2017 10:06 pm
by Pacman
I've received the drive and indeed, this Sony MPF-920 Z/121 (April 2009) has a BH9558KV chip (the square PLCC shaped one marked "IC1").
The other chip (a smaller rectangular shaped SMD chip marked "IC2") is a BD6861FS. So no Sony IC as with my previous drive.
What I've done so far is change the drive ID to "SEL 0" (drive 0) instead of using the factory setting of "SEL 1" (drive 1) and of course inserted the flat data cable upside down in the drive. It works perfectly in the Mega STe with both HD and DD floppies! :D

So now I've confirmed that the drive works as it should (or so it seems to far -I haven't done any extensive tests) with my Mega STe (equipped with an AJAX chip) I'm going to continue with the installation of that drive inside an STe along with the Exxos version 6 HD module kit but I'm a little confused about some details.
Back in the day (before I ever got round to actually building an HD module) I looked into this subject a lot and concluded (based on Atari newsgroup and mail discussions) that 3 things needed be done for preparing a Sony MPF 520 or MPF920 drive to work with an ST in both HD and DD modes:

(A) change the drive ID to "Drive 0" instead of "Drive 1"
I believe this is mandatory for the drive to be identified at all on an Atari.

(B) short (put a wire across) the two pins of the "CTIN" disk detect switch (near the front of the drive -where the floppies are inserted).
This forces the ST into understanding whenever a floppy has been removed and replaced with another one (media change) so it won't think the first floppy is still there and thereby mess up things

(C) connect a wire between one of the pins of the HD detect switch (it detects the additional hole in HD floppies) to pin 2 of the flat-cable connector (34 pin Shugart) on the drive, then connect another wire from the same pin 2 to the HD module's high density detect input.
On the "HDIN" switch you should use the pin which is not connected to GND, which in the case of this drive is the lowest pin (as Exxos has shown in a photo of the floppy drive on this page -scroll down the page almost half way where the "HD wire" is clearly marked)

That's my notes from back in the 90s, but it differs for the most part from Exxos' info:

(A) changing the drive ID to "drive 0" is correct

(B) Exxos doesn't short the "disk detect" (CTIN) switch, hence my confusion as back in the day I was told ny numerous Atari users that this was absolutely necessary, because it forces a media change, unlike the PC method of doing it.
Exxos explains the media change issue here, but since there's no mention of shorting the CTIN switch, does this mean that the floppy drive when used together with the Exxos v6 HD module, doesn't need to have this switch shorted in order to function properly (because that HD module is more advanced than the ones available back in the late 90s), or are there just different views on the matter?

(C) While Exxos' solution also takes the HD detect signal from the "HDIN" switch over to the HD module, there's no mention of connecting it to pin 2 of the 34-pin Shugart connector on the drive as well. I believe I was told back in the day that pin 2 of the drive needed this signal in order to understand when to set the drive into HD or DD mode. Recently I've understood that there's common confusion about pin 2 being an input or output pin for that signal and here I read that on a normal ST/STE it's an output signal while on a Mega STe it's an input signal, with even more info here (which still confuses me).

Does this then mean I do need to attach the wire to pin 2 of the Shugart connector when using it with my STe while with the Mega STe I should remove it (or it doesn't matter if it's still there), the other way round, or just don't connect anything to pin 2 at all?

Re: Choosing between three Sony MPF-920 drives

Posted: Mon Sep 25, 2017 10:21 pm
by exxos
You don't need to mess about with the MPF920 drive, you just need the HD select wire..

Media detect is done properly in the HD6 module. I doubt those old hacks worked anyway.

You can't compare "old" information with current tech, if you try you will just end up confused...

Just follow the install guide and stop looking for ways to over complicated everything ;)

Read HD6 info here... ... dex.htm#V6

Re: Choosing between three Sony MPF-920 drives

Posted: Wed Sep 27, 2017 12:51 am
by Pacman
Yes, that's true :D

I suppose this means that your HD module doesn't need any more drive modification than just adding the HD select wire (and drive 0 change) because of added logic that the HD modules from other back in the 90s didn't have?

How about for use with the Mega STe? It seems to work fine in both HD and DD modes with the added modifications I explained so I guess "if it works don't fix it" meaning I probably shouldn't remove it :lol:

Alas the joy with the new drive didn't last because I accidently knocked it out of alignment. By trial and error I've managed to adjust its position so that it partly works (using a formatting program, then slightly changing its position every time the drive "hickups" not finding the tracks. This way I've gotten it to format almost 3/4 of a full disk).
I've read about alignment disks, but they're probably more rare and expensive than a new Sony MPF-920 drive so I'm wondering if there are any other ways to work this out? Any suitable software on the ST for this sort of thing?

Re: Choosing between three Sony MPF-920 drives

Posted: Wed Sep 27, 2017 9:34 am
by exxos
I'm not aware of anything for alignment, or anyone who's even attempted it before.

Re: Choosing between three Sony MPF-920 drives

Posted: Sun Oct 01, 2017 12:07 am
by Pacman
I've looked into it further and understood you need:

a) an alignment floppy disk
b) alignment software (I've been told the official Atari diagnostic cartridge can do this)
c) a dual channel oscilloscope

so my conclusion is that for just one drive it's just not worth it. Perhaps for servicing multiple drives though.

I've been told I can get another MPF-920 from a PC user who doesn't need it :)
It's a 2001 E/131 model but I figure it's worth a go anyway.
I suppose if it won't work with my ST and turns out to have a Sony chip I can always exchange it with the PCB from my (now misaligned) 2009 Z/121 drive (which has a BH chip). I did notice that the head/head-servo cables could be removed and I suppose the same goes for the main motor as well.

When I get it all up and running I'll probably do the capacitor modification as well which you've described here (for others interested). It describes how to solder an SMD resistor in parallel with the existing electrolytic capacitor for the spindle motor in case it goes bad (as electrolytic capacitors do after a while) and keeps the 5V power for it to be stable.