- The LaST Upgrade -


exxos 2013 - First documented 2007


How to alter the none jumper versions of the SONY MPF920 1.44 drive to work on Atari ST etc.

NOTE: While you can use this drive to replace a old (broken) 720K drive, simply swapping the drive does not allow 1.44 floppys to work. You need a upgrade such as THIS ONE.


There seems to be a few revisions of this drive. The drives I have are dated APR2009, though I also have a 2000 & 2003 drive stamped "MPF920-E". The 2000 drive does not work in swapping the drive ID jumper which uses a Sony chip. Its possible my drive could have been faulty, but I can no longer confirm this as all later drives had a BH chip. I will assume for now that the Sony chipped drives will not work as a internal drive on the Atari.

The 2009 & 2007 drive is stamped "MPF920". I will assume somewhere between 2000 - 2003 that Sony stopped using there own floppy IC and started using the BH device. I will assume any MPF920 drive will be good regardless of revision if it is dated past 2003.

This does not mean other drives will not work. I have had drives dated around 1995 which worked, though I did not make any notes on the labels. Older drives I believe worked , they normally had jumper links on the back. Though I cannot confirm this as I do not have any of those drives anymore.

If anyone has any other versions which do work then please send me a image and let me know the chip number and SEL locations on the PCB and I will include them here. Also if anyone find any other drives capable of all extended formats then please let me know.

I doubt any manufactures still make floppy drives now. Sony stopped I presume in 2009 as I have not seen any drives dated past that date. If there is any drives still being produced which work then please let me know.

The jumper links are located on the back of the drive (middle right on above image) While these were changed back and forth, this drive refuses to work in DRIVE B mode. Either the drive is faulty or it is a bad revision of the drive. I also noticed that the "faulty" drive has a SONY chip stamped on it, whereas the working drives just have "BH955"

It would be better to use a MPF920 drive which uses the BH966 IC. From the drives I have seen, any dated past 2006 seem good.

To mod the drive first take out the 3 screws on the bottom of the drive and it reveals the PCB. Note the front floppy bezel is clipped into the bottom plate so care must be taken to push the plastic clips in gently to free the metal work from the bezel.
SEL1 is bridged with a zero ohm link by default from manufacture.

The link is moved to SEL0 with a soldering iron. That's it! Your drive has now had its drive select ID altered to work with your ST!

Note that with 1.44 drives you must reverse the ribbon cable ( Twist and put it in upside-down).

There has been various talks in the past about modding the media change line on the Atari's to prevent corruption of the FAT tables. I am not aware of any reliable methods to do this. There have been mods to connect pin1 of the floppy connector to a switch to trigger it on floppy changes, but according to the ST's schematics, this wire is GND anyway.

As far as I am aware, TOS104 works good for floppy access. If using GEM, at worst, all you have to do is press ESC to refresh the window and read the current floppy's boot sector/FAT so there is no problems anyway.

I have noticed in previous versions of TOS that pressing ESC does not read the floppy contents but only refreshes the window from a chanced FAT in memory. It is probable that this would lead to floppy corruption but TOS104 and above seem ok in this respect.

UPDATE- My latest revision floppy kit now includes the media change fit. See HERE

UPDATE March 14, 2016

After testing 4 drives out dated JUN2002 on my ST, these all failed to work. I tried one on my stock falcon and while it worked, it was unreliable. A later drive worked perfectly. So again the SONY chips are questionable. It is difficult to say if the "E" version is to blame, or it was the year of manufacture to blame. I will try and keep a list of the drives I come across.. I am marking drives as BAD if they have a SONY chip. I never tested if the drives worked correctly as a PC drive or not as I have only been using them on a Atari ST/Falcon.

APR 2000 - SONY CHIP - BAD (E/131)
xxxx 2001 - SONY CHIP - BAD
JUN 2002 - SONY CHIP - BAD (E/131)
JAN 2003 - Unknown - possible good BH chip (E/131)
MAY 2004 - BH CHIP - GOOD (Z/131)
DEC 2005 - BH CHIP - GOOD (Z/121)
OCT 2006 - BH CHIP - GOOD (Z/121)
JUL 2007 - BH CHIP - GOOD (Z/121)
xxxx 2008 - Unknown - possible good BH chip
APR 2009 - BH CHIP - GOOD (Z/121)



UPDATE November 26, 2023

It is possible the problems with chipset used may be a side-effect of inadequate pull-up resistors on the drive. See fixes HERE for more information.