exxos's Atari, Amiga & retro forum

While there can be a lot of reasons for the floppy drive to fail, such as bad PSU, bad drive etc. If a drive works in a PC but not a STE for example, then its possible the machine may need the fix below.

The short version of this fix , is that the original Atari floppy drives had internal pull ups on some of the signals, drives like the MPF920 do not. So its possible (and likely) All non-original drives will need this modification. It is possible original drives could suffer as well, but this is a very new fix and the "bug" has only just been found.

This issue can cause the drive not to be found, intermittent read/write issues etc This issue is likely present on any machine with a 1772/Ajax floppy controller using a LS06 type buffer. IIRC the MSTE had 1 of these resistors fitted, I need to look into that again..


Below, the points in red need a 1K resistor connecting to 5V.


I did a quick example below...

FALCON MOD

Basically the same as above, but on U35 on the Falcon. PIn4 already has a pull-up so there is no need to add another one.

This is one of my last fixes I would like to do in my STFM before closing the case so to speak. The is locating the chip on this machine as it may not be in the same/similar location. I have a HD7406P in socket U14 on my board which has the same pin count. Is this the same/similar chip?

Should be yes. Must be s old machine not to have a LS variant.

Managed to find this, it looks like the pin layout is the same too.

https://www.futurlec.com/74/IC7406.shtml