5.25 floppies that read but don't write

Mike Stein mhs.stein at gmail.com
Sat Aug 22 10:34:22 CDT 2015

Do we know the make/model of this drive?

----- Original Message ----- 
From: "Marc Verdiell" <marc.verdiell at gmail.com>
To: <cctalk at classiccmp.org>
Sent: Saturday, August 22, 2015 12:50 AM
Subject: RE: 5.25 floppies that read but don't 

> Chuck,
> I looked at the pin 2 signal and resulting drive 
> behavior. It doesn't
> properly auto-switch between densities as it 
> should. It does switch it for
> reading, but not for writing. Below is the full 
> story.
> There is one jumper that controls DD/HD 
> switching mode.
> In the auto position, I can read both HD and DD 
> formats (I use the right
> diskettes for either format). You can see the 
> computer on pin 2 (density
> select) trying both positions, settling on the 
> right one (high for HD, low
> for DD), and reading the disc correctly.
> That's great. But when writing, although pin 2 
> goes to the right level, the
> floppy seems to ignore it. It will always write 
> at DD, and refuse to write
> in HD (no signal at the head).
> Interestingly, in the fixed density position 
> (should be HD only), it WILL
> write at 1.2M HD! The write signal does appears 
> at the head. Unfortunately
> in this setting it will NOT switch the reading, 
> get stuck reading only DD
> and fail on HD.
> So I can either have the reading HD or the 
> writing HD, but not the two at
> the same time. That's why a regular format 
> fails. The density switching
> logic seems to have a problem. Rather than track 
> down which IC or transistor
> failed on the board it might be much simpler to 
> get another 5.25 floppy. In
> the meantime my understanding of these simple 
> critters has improved a lot.
> Marc
>>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"?

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