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 , incorrect drive id etc. If a known working drive works in a PC or in another machine but not in another, then it's possible the machine may need the pullup fix as stated below.

There is a lot of variation on pullup values built into drives that are simply inadequate and can be as high as 500K or may simply be missing all together. It is impossible to know what drives will malfunction as there are simply to many drives produced to realistically test them all. In general my findings were based on the MPF920 series of drive and some original drives where the added pullups solved the problems with intermittent drive failing issues. Adding a 1k resistor ensures your drive does not suffer from such problems.

Also note DMA issues can also causes issues for any attached drive regardless . I would recommend doing that mod first.

Below, the points in red need a generic 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