5 Jun
2023
5 Jun
'23
1:43 p.m.
Message: 21
Date: Mon, 5 Jun 2023 04:35:28 +0100
From: Tony Duell <ard.p850ug1(a)gmail.com>
Subject: [cctalk] Re: Getting floppy images to/from real floppy disks.
On Sun, Jun 4, 2023 at 10:57 PM Fred Cisin via cctalk
<cctalk(a)classiccmp.org> wrote:
>
> On Sun, 4 Jun 2023, Rick Bensene via cctalk wrote:
<> > an example of early "mobile computing". (Tongue firmly in
cheek).
The original Osborne 1 had a 12V power input!
Actually it's +12.6V and +5.6V and you have to supply both voltages.
It's one diode drop to the +5V (logic supply) and +12V (DRAM, disk
motors, monitor supply), the -5V for the DRAM is produced on the logic
board.
I am told it was never used and that the Osborne battery pack came
with an inverter to provide 110V AC.
-tony
5 Jun
5 Jun
7:41 p.m.
New subject: Getting floppy images to/from real floppy disks.
On Monday, June 5th, 2023 at 1:43 PM, Robert Feldman via cctalk
<cctalk(a)classiccmp.org> wrote:
It (the Osborne Powr-Pac (tm) ) has a what the manual says is a DC-DC inverter that
plugged into a Gould lead-acid battery (or the cigarette-lighter socket in a car) at one
end and the AC input of the Osborne 1 at the other. I have read on this list that Lee
denies that OCC ever sold them, but I have one that I bought for $50 at Compumat in
Chicago on October 10, 1983 -- I still have the unit, receipt, and User Registration card.
It came with a glossy-printed grey-and-blue manual, like other contemporary OCC products.
If anyone wants a copy, I can email you a PDF scan of the user manual.
Bob
It's funny that luggable power packs come up here as I'm trying to revive my
Otrona Attache... The power supply does nothing on AC input, even after a recapping, so I
thought I'd investigate the "DC Power Option" described in the manual.
Unfortunately I can't find any record that Otrona ever actually *sold* a "DC
Power Option", which would plug into an unpopulated 6-pin Molex connector on the back
of the device. Interestingly, the header inside the power supply labeled "DC
Option" is a 7-pin header, so I'm not sure which pin was "optional" for
the external connector!
I'd just replace the power supply wholesale with a little ATX supply or something, but
the machine needs 5V, 12V, -12V, and 15V; the latter is used to power the CRT and
represents a real challenge! I've yet to find anything that outputs all 4 levels at a
reasonable price.
john
Message: 21
Date: Mon, 5 Jun 2023 04:35:28 +0100
From: Tony Duell ard.p850ug1(a)gmail.com
Subject: [cctalk] Re: Getting floppy images to/from real floppy disks.
On Sun, Jun 4, 2023 at 10:57 PM Fred Cisin via cctalk
cctalk(a)classiccmp.org wrote:
> On Sun, 4 Jun 2023, Rick Bensene via cctalk wrote:
<> > an example of early "mobile computing". (Tongue firmly in
cheek).
The
original Osborne 1 had a 12V power input!
Actually it's +12.6V and +5.6V and you have to supply both voltages.
It's one diode drop to the +5V (logic supply) and +12V (DRAM, disk
motors, monitor supply), the -5V for the DRAM is produced on the logic
board.
I am told it was never used and that the Osborne battery pack came
with an inverter to provide 110V AC.
-tony 
8:42 p.m.
New subject: Getting floppy images to/from real floppy disks.
On Tue, Jun 6, 2023 at 3:42 AM John Floren via cctalk
<cctalk(a)classiccmp.org> wrote:
It's funny that luggable power packs come up here
as I'm trying to revive my Otrona Attache... The power supply does nothing on AC
input, even after a recapping, so I thought I'd investigate the "DC Power
Option" described in the manual. Unfortunately I can't find any record that
Otrona ever actually *sold* a "DC Power Option", which would plug into an
unpopulated 6-pin Molex connector on the back of the device. Interestingly, the header
inside the power supply labeled "DC Option" is a 7-pin header, so I'm not
sure which pin was "optional" for the external connector!
I'd just replace the power supply wholesale with a little ATX supply or something,
but the machine needs 5V, 12V, -12V, and 15V; the latter is used to power the CRT and
represents a real challenge! I've yet to find anything that outputs all 4 levels at a
reasonable price.
I consider the PSU to be as much a part of the original design as any
other part of the machine and like to keep them original.
The schematic for the power supply is in the technical manual. It
appears there's a startup supply using the mains-frequency transformer
T1 as well as the SMPSU part. If that's missing then I'd suspect
something around the mains input side. I assume the fuse is good!
The power switch is a little odd in that it uses the triac Q1 to
switch the mains, controlled by the user switch. Maybe check round
that area.
-tony
11 Jun
11 Jun
1:07 p.m.
New subject: Getting floppy images to/from real floppy disks.
On Mon, Jun 5, 2023 at 1:43 PM Robert Feldman via cctalk <
cctalk(a)classiccmp.org> wrote:
It (the Osborne Powr-Pac (tm) ) has a what the manual says is a DC-DC
inverter that plugged into a Gould lead-acid battery (or the
cigarette-lighter socket in a car) at one end and the AC input of the
Osborne 1 at the other. I have read on this list that Lee denies that OCC
ever sold them, but I have one that I bought for $50 at Compumat in Chicago
on October 10, 1983 -- I still have the unit, receipt, and User
Registration card. It came with a glossy-printed grey-and-blue manual, like
other contemporary OCC products.
If anyone wants a copy, I can email you a PDF scan of the user manual.
Bob
Bob,
I asked Lee if he could respond to this and here it is:
"While I don’t recall saying that, I may well have - I know that I was
involved in the engineering question of how safe it would be to use.
The inverter produced 230 VDC, which it turned out could be safely fed to
the 120VAC input without more than a single diode drop reverse voltage
across an electrolytic filter capacitor. This was due to the power supply’s
design having a voltage doubler as the first stage.
It was designed by a third party who presented it to Osborne who accepted
it as a branded product - exactly how they supplied it is something I don’t
know (did the third party handle the production or did we?).
If the question had ben posed to me as to whether it was a “battery pack” I
might well have answered no because it never included batteries.
Apologies for any confusion - I was always overloaded at Osborne and no one
knew what a VP of Engineering’s job was until John Hanne came in in 1983.
I was relabeled “R&D Fellow” in 1981 and replaced with Ed Richter."
(I did get Lee's permission to post this, which was the cause of the delay
in posting this as he hadn't seen my first request.)
Sellam
Message: 21
Date: Mon, 5 Jun 2023 04:35:28 +0100
From: Tony Duell <ard.p850ug1(a)gmail.com>
Subject: [cctalk] Re: Getting floppy images to/from real floppy disks.
On Sun, Jun 4, 2023 at 10:57 PM Fred Cisin via cctalk
<cctalk(a)classiccmp.org> wrote:
>
> On Sun, 4 Jun 2023, Rick Bensene via cctalk wrote:
<> > an example of early "mobile computing". (Tongue firmly in
cheek).
The original Osborne 1 had a 12V power input!
Actually it's +12.6V and +5.6V and you have to supply both voltages.
It's one diode drop to the +5V (logic supply) and +12V (DRAM, disk
motors, monitor supply), the -5V for the DRAM is produced on the logic
board.
I am told it was never used and that the Osborne battery pack came
with an inverter to provide 110V AC.
-tony
5:24 p.m.
New subject: Getting floppy images to/from real floppy disks.
I'm a bit surprised that there don't seem to be any adaptations that
hook into the head pre-amps and use an ADC to give a view of what the
read signal actually looks like. Maybe that's asking too much--there
are certainly MCUs with sufficiently fast ADCs and memory to do this.
--Chuck
8:35 p.m.
New subject: Getting floppy images to/from real floppy disks.
On Mon, Jun 12, 2023 at 1:25 AM Chuck Guzis via cctalk
<cctalk(a)classiccmp.org> wrote:
I'm a bit surprised that there don't seem to be any adaptations that
hook into the head pre-amps and use an ADC to give a view of what the
read signal actually looks like. Maybe that's asking too much--there
are certainly MCUs with sufficiently fast ADCs and memory to do this.
I suspect that would be too drive-specific for most users.
Yes the head preamp outputs are nearly always available on testpoints
on the drive PCB (you use them when doing a head alignment) but having
to find them and connect to them could be non-trivial.
At least with the flux transition interfaces all you have to do is
plug into the normal drive ribbon cable connector.
-tony
8:48 p.m.
New subject: Getting floppy images to/from real floppy disks.
On Sun, Jun 11, 2023 at 9:07 PM Sellam Abraham via cctalk
<cctalk(a)classiccmp.org> wrote:
"While I don’t recall saying that, I may well
have - I know that I was
involved in the engineering question of how safe it would be to use.
The inverter produced 230 VDC, which it turned out could be safely fed to
the 120VAC input without more than a single diode drop reverse voltage
across an electrolytic filter capacitor. This was due to the power supply’s
design having a voltage doubler as the first stage.
I find that curious (read : I don't see how it could work, at least
not reliably.)
The power supply in the Osborne 1 and 1A is an Astec SMPSU. The input
stage is the conventional one. Mains input goes through a filter
circuit to a bridge rectifier. The output of the bridge rectifier goes
to 2 electrolytic capacitors in series. There is a voltage selector
link between one side of the AC input to the bridge rectifier and the
centre tap of the capacitors.
In the Osborne 1, this link is hidden on the PSU board and you have to
dismantle the machine to get to it. On the 1A it's set by a little
plug-in PCB in the mains input module on the back which you turn round
for 115V or 230V mains.
On 115V the link is in place. 2 of the diodes in the bridge and the 2
capactors form a voltage doubler circuit. Each capacitor charges to
about 160V. You get 320V across the pair to feed the chopper.
On 230V, the link is open. The bridge rectifier works as you might
expect, the 2 capacitors get around 320V across them and charge
equally (so about 160V on each). Again 320V to the chopper.
Now if you feed in 230V DC with the link in the 115V position, one
capacitor (only) will charge to the full 230V. That is more than the
working voltage of said capacitor. The other will not charge at all
from the input. Meaning the chopper circuit is fed from the charged
capactior with another one in series. That one is liable to charge up
with a reverse polarity due to the action of the chopper.
Bang!
-tony
341
days inactive
348
days old
6 comments
5 participants
participants (5)
-
Chuck Guzis -
John Floren -
Robert Feldman -
Sellam Abraham -
Tony Duell