5.25 floppies that read but don't write

Marc Verdiell marc.verdiell at gmail.com
Fri Aug 21 02:01:37 CDT 2015

Thanks Chuck. Looks like you are on to something, I'll search in this
direction. Unlikely it has anything to do with the disks themselves, which
were blank. The 500 kHz write signal present on the connector just doesn't
make it to the head, whereas the 300 kHz does. On the other handm something
along what Chuck suggests could create this exact problem. I'll let you know
how it goes. 
I am aware of the narrow track problem of 360k written by HD drives, so I
have other native 360k DD drives for that purpose. For now I just want my HD
drive to behave as one ;-)

>At high density, have you taken a good look at pin 2 of the floppy 
>interface?  Have you checked to see if pin 2 is configured (via jumpers) 
>as "density select"?    Various drives have different jumperings for 
>pins 2 and 34 (and sometimes 4).  For example, I deal with some Japanese 
>CNC gear that uses pin 2 for disk change and pin 34 for read (and pin 4 
>for "in use".

>> So I tried to force formatting in DOS at 360k, and sure enough it
>> worked! I can then read the diskette back, write on it, etc... And of
>> course it failed formatting at 1.2 Mb. But the drive (Chinon FR-506)
>> is a 1.2M one, and reads fine at 1.2M! Any clue? Is there a drive
>> setting that would prevent it to write at high density but let it do
>> at low density?

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