Need manual for a floppy drive...

Tony Duell ard.p850ug1 at
Mon Jan 30 10:36:28 CST 2017

On Mon, Jan 30, 2017 at 4:05 PM, geneb <geneb at> wrote:
> On Sun, 29 Jan 2017, Chuck Guzis wrote:
>> On 01/29/2017 12:13 PM, geneb wrote:
>>> I would assume that the jumper configuration I'd set would have done
>>> that - it has two settings, "UA" - front led handled by the In Use
>>> signal and "DA" - front led handled by the Drive Select signal.  My
>>> K4 has a pair of Shugart 455's in it (that work fine), but I REALLY
>>> don't want to go to the hassle of pulling a drive out in order to see
>>> if the jumper settings match. :)  It may come to that though.
>> Take a look at the drive (I've got a JU-455 here and there's a
>> 2-position jumper with positions labeled UA and DA (roughly the middle
>> of the PCB, next to the MM/MS jumper.   With UA  jumpered, the LED will
>> light only on the INUSE signal; with the DA position, the LED with light
>> with drive select.
> The activity light doesn't work in either setting.

Now I am confused...

I've downloaded the Shugart 455 service manual from bitsavers. By
the looks of things the jumper in question is the one to the left of the
control logic ASIC, between a 74LS38 and a 74LS74. It has 2 positions,
to the left DS (Drive Select), to the right UO (In use).

According to the schematic, in the DS position, the LED is not
controlled by the ASIC. The DS signal (active high drive select)
is fed to the input of U7Ba (7406), the output of which has
the LED and a 220R resistor to +5V. DS goes high, the output
transistor of the 7406 gate turns on, LED lights.

If that's the right schematic, it should be easy enough to debug.


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