Re: Need an 8280 formatted 8" disk (progress!)

From: Ethan Dicks <>
Date: Mon, 13 Feb 2017 17:09:32 -0500
Message-ID: <>
On Mon, Feb 13, 2017 at 4:49 PM, Rob Clarke <> wrote:
> Some progress has been made.  Thanks to Ethan's suggestion of trying B-R and
> B-W to check the stepper operation I realised that track 0, sectors 1-26 are
> readable and writable successfully...

Very cool.

> ... which shows that all the read/write
> circuitry is good, as is at least side of my media. It also shows that my
> attempts to format the disks at least started successfully.


> If I understand the sector numbering scheme correctly, side 0 has sectors
> 1-26 and side 1 has sectors 33-58. I can't read anything from track 0,
> sector 33 (26-32 give illegal T/S errors), so it looks like it gave up once
> we reached side 1. Now I understand a bit about the 8" formats, it's clear
> that my disks are officially single sided, but looking at the schematic for
> the 848-2 on zimmers, it has both index hole sensors, but I am not sure
> whether the signalling from the logic is equal, so maybe this is the issue?

Ah... well... If you are using SS media in this drive, it will
apparently detect that and treat it as SS...

From the TM-848 manual (on

"2. The TM848-2E has two index sensors, each consisting of an infrared
L.E.D. light source and a phototransistor, positioned to generate a
signal when an index hole on the diskette is detected. The drive can
determine if a singlesided or double-sided diskette is installed. This
output signal is present at the interface"

You should probably check the value of pin 10 on the drive... it's
probably telling you it found a single-sided disk and the onboard
microprocessor might be declining to write the data to the "back side"
of SS media.

If you can find some DS media or make a new hole in one of the ones
you have (and cover the other index hole), you might get farther.

> My next plan is to cut an extra index hole to make it look like a double
> sided disk, has anyone got one to hand who can measure the offset of the
> index hole for me?

I probably have both types handy (I recently helped rescue a pile of
old gear and got hundreds of used 8" floppies - mostly DEC RX01
(single-sided) but a few were from a 3rd-party disk drive (which I did
not get) that did DSDD.  Later tonight if nobody else has responded, I
can get some pix.

OTOH, If the back of the media has any bad sectors, you might not get
100% satisfaction.  There was a time when media sheets were tested and
ones with defects on one side were packaged and sold as SS diskettes.
Later, the QC got better and everything mostly passed, so the prices
and the boxes were different but the media was pretty much identical
for SS and DS.  People were used to buying SS media for less so that
continued.  Many people had good luck (and a few people had bad luck)
with "flippy disks" in that era.


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Received on 2017-02-13 22:09:32

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