Re: New user asking for help
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r...@speakeasy.net
Nov 10, 2012, 5:54:14 PM11/10/12
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Hi Keith,
Just a guess, but since the "standard" 8-inch floppy interface is a 50-pin connector, might it be that the two 25-pin DB connectors are a (poor) substitute for that interface? Of course, 25 pins of the 50-pin connector are grounds, so it would be easy enough to check if the two connectors go separately to each floppy, or are a common interface. There are 4 drive select lines on the "standard" 50-pin interface. Unless there are additional electronics in the wooden enclosure, I doubt that there is anything "serial" about this thing at all.
I believe that there are motor on and head load pins on the "standard" interface, so it would probably be easy to drive them with something like a Raspberry Pi to make it look like it's working? Don't know.
Where'd you get the Raspberry Pi? I'd love to get one to play around with.
Roger
cory
Nov 10, 2012, 11:30:03 PM11/10/12
to Cromemco
Hi All,
Second version of this message because the first was accidentally sent
to the author instead of the group as a whole.
I disassembled the PFD tonight and took some pictures. This one here:
http://i.imgur.com/v5dVb.jpg shows the drive after it has been removed
from the casing. The only additional equipment inside the case is a
power supply, and the back of this drive shows the flat slot type 50-
pin connector on the back. I believe it is the same as what would be
found on an internal drive. I believe Keith is correct that the two
DB25 connectors is simply an off-the-shelf alternative to creating a
50-pin external connector.
Looking at specs for the 34-pin floppy drive connector in modern PCs
(the few that still have a FDC), I found that there is a simple pair
of pins that can be used to engage the motor of the drive, which would
be adequate to create the desired illusion. However, I know that this
8-inch drive is a different beast altogether and so I don't know where
to start. The 4 drive select pins are probably one for each drive +
matching signal ground lines, and knowing where this information came
from could open the door for me. Can you let me know what else you
know and where that knowledge originated?
Second version of this message because the first was accidentally sent
to the author instead of the group as a whole.
I disassembled the PFD tonight and took some pictures. This one here:
http://i.imgur.com/v5dVb.jpg shows the drive after it has been removed
from the casing. The only additional equipment inside the case is a
power supply, and the back of this drive shows the flat slot type 50-
pin connector on the back. I believe it is the same as what would be
found on an internal drive. I believe Keith is correct that the two
DB25 connectors is simply an off-the-shelf alternative to creating a
50-pin external connector.
Looking at specs for the 34-pin floppy drive connector in modern PCs
(the few that still have a FDC), I found that there is a simple pair
of pins that can be used to engage the motor of the drive, which would
be adequate to create the desired illusion. However, I know that this
8-inch drive is a different beast altogether and so I don't know where
to start. The 4 drive select pins are probably one for each drive +
matching signal ground lines, and knowing where this information came
from could open the door for me. Can you let me know what else you
know and where that knowledge originated?
Mike Stein
Nov 11, 2012, 1:31:27 AM11/11/12
to crom...@googlegroups.com
Pinouts on the old drives weren't always standardized, so it might help to
tell what make & model it is; I can't tell without seeing the front but
maybe someone else will. Shugart? Tandon? Schematics and pinouts are
available for most of them.
Not much to it; most 8" drives run constantly when powered up; to select and
light the LED just connect whichever drive select it's jumpered for to its
adjacent ground pin. If you want to actually step the head, there is a step
pin and a direction pin.
What specifically do you want to do? Light the LED, spin the motor, make
stepping and head load sounds?
Seems like a bit of a waste if the drive is actually functional; maybe
someone would love to trade a broken one that still goes through the motions
for it...
mike
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tell what make & model it is; I can't tell without seeing the front but
maybe someone else will. Shugart? Tandon? Schematics and pinouts are
available for most of them.
Not much to it; most 8" drives run constantly when powered up; to select and
light the LED just connect whichever drive select it's jumpered for to its
adjacent ground pin. If you want to actually step the head, there is a step
pin and a direction pin.
What specifically do you want to do? Light the LED, spin the motor, make
stepping and head load sounds?
Seems like a bit of a waste if the drive is actually functional; maybe
someone would love to trade a broken one that still goes through the motions
for it...
mike
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Martin Eberhard
Nov 11, 2012, 12:29:39 PM11/11/12
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This is the standard setup for the PFD - Cromemco built it with two DB25 connectors, so that it would go through the back panel of the Z-1 computer easily. The "normal" 50-pin Persci interface is split between two connectors, and comes back together with the Cromemco cable to the floppy controller board. I have this exact setup on my Z-1 computer.
The Persci interface is not the same as the more common Shugart disk drive interface. It is possible to connect a Shugart 8" disk drive to a PC - I have done so myself. The Shugart interface is almost the same as the interface to 5.25" and 3.5" disks, and requires just a bit of hardware to make it work perfectly.
On the other hand, the Persci drives have a unique mechanism for seeking tracks - the controller issues a series of Seek commands (at a very high speed), and then waits for a "seek complete" response from the Persci drive. Persci's pinout on the 50-pin interface is different than that of the Shugart (and PC) drives, and includes several signals that are Persci-unique - such as Seek Complete, Restore, and Eject.
A word of caution: Having restored three Persci drives now, I can assure you that the tantalum capacitors on your Persci drive are most probably bad, and you will damage the drive if you power it on. All of the tantalums that are on the 24V power supply should be replaced before you ever power it on. (In my experience, 75% of these capacitors have failed.)
Also, the Persci drive requires a somewhat tricky alignment job - requiring either an alignment fixture or some software that simulates the Persci fixture. I use a program called "SIMU" that runs on a SOL20 to do this alignment. This is non-trivial, and you won't be able to get it working without going through the correct procedure...
Feel free to email me privately for details.
Martin
The Persci interface is not the same as the more common Shugart disk drive interface. It is possible to connect a Shugart 8" disk drive to a PC - I have done so myself. The Shugart interface is almost the same as the interface to 5.25" and 3.5" disks, and requires just a bit of hardware to make it work perfectly.
On the other hand, the Persci drives have a unique mechanism for seeking tracks - the controller issues a series of Seek commands (at a very high speed), and then waits for a "seek complete" response from the Persci drive. Persci's pinout on the 50-pin interface is different than that of the Shugart (and PC) drives, and includes several signals that are Persci-unique - such as Seek Complete, Restore, and Eject.
A word of caution: Having restored three Persci drives now, I can assure you that the tantalum capacitors on your Persci drive are most probably bad, and you will damage the drive if you power it on. All of the tantalums that are on the 24V power supply should be replaced before you ever power it on. (In my experience, 75% of these capacitors have failed.)
Also, the Persci drive requires a somewhat tricky alignment job - requiring either an alignment fixture or some software that simulates the Persci fixture. I use a program called "SIMU" that runs on a SOL20 to do this alignment. This is non-trivial, and you won't be able to get it working without going through the correct procedure...
Feel free to email me privately for details.
Martin
Martin Eberhard
Nov 11, 2012, 12:42:39 PM11/11/12
to crom...@googlegroups.com
Indeed - Cory: I would love to buy this drive from you (at a significant margin above your original investment!)... I am very interested in restoring these Persci drives to their original operating condition. Let me know if you would consider selling it.
Best,
Martin
Best,
Martin
cory
Nov 14, 2012, 6:27:57 PM11/14/12
to Cromemco
Hi Martin,
I have powered it up at least twice in the last couple years, to eject
the disk and show it off to folks who have never seen an 8" floppy, so
I hope that there's no damage done (the ejection mechanism works
great). I disconnected the drive from the power supply and turned on
the power supply to test it and the +5V post tested at 5.00V, the -5
post at -5.04, but the +24V post was dead (0.00V). The test points I
used appear to be directly off the transformer, before the capacitor
comes into play. I hope that means that no damage has been done to the
drive itself.
I am truly conflicted whether I should proceed with my project or hand
this over to someone who would repair it and preserve its value as an
antique.
> >http://i.imgur.com/v5dVb.jpgshows the drive after it has been removed
> > To post to this group, send email to crom...@googlegroups.com<javascript:>.
I have powered it up at least twice in the last couple years, to eject
the disk and show it off to folks who have never seen an 8" floppy, so
I hope that there's no damage done (the ejection mechanism works
great). I disconnected the drive from the power supply and turned on
the power supply to test it and the +5V post tested at 5.00V, the -5
post at -5.04, but the +24V post was dead (0.00V). The test points I
used appear to be directly off the transformer, before the capacitor
comes into play. I hope that means that no damage has been done to the
drive itself.
I am truly conflicted whether I should proceed with my project or hand
this over to someone who would repair it and preserve its value as an
antique.
>
> > To unsubscribe from this group, send email to
> > cromemco+u...@googlegroups.com <javascript:>.
> > To unsubscribe from this group, send email to
Martin Eberhard
Nov 14, 2012, 9:20:41 PM11/14/12
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Hi Cory,
Yes, the caps on the 24v line are the ones that fail, and they fail to a short circuit :-(. This means that powering it up will probably do damage, and the more it is powered, the more damaged. Unfortunately, there is no fuse on the 24V supply.
If you decide you want to sell it, please let me know- I am interested, and I am (think) one of the few remaining people who know how to get them running.
Cheers,
-Martin
FYI,
in the back of my napkin, I hope you’ve proactively fast tracked sufficient mission critical bandwidth to close the loop on leveraging global synergies ASAP up the flagpole. We’ll keep moving forward by encapsulating knowledge based best practice cookie cutter core asset skill set solutions in this collaboration task game plan thinking outside of the black box.
--Pasted from my game changing brand recognized business phone
> To post to this group, send email to crom...@googlegroups.com.
> To unsubscribe from this group, send email to cromemco+u...@googlegroups.com.
Yes, the caps on the 24v line are the ones that fail, and they fail to a short circuit :-(. This means that powering it up will probably do damage, and the more it is powered, the more damaged. Unfortunately, there is no fuse on the 24V supply.
If you decide you want to sell it, please let me know- I am interested, and I am (think) one of the few remaining people who know how to get them running.
Cheers,
-Martin
FYI,
in the back of my napkin, I hope you’ve proactively fast tracked sufficient mission critical bandwidth to close the loop on leveraging global synergies ASAP up the flagpole. We’ll keep moving forward by encapsulating knowledge based best practice cookie cutter core asset skill set solutions in this collaboration task game plan thinking outside of the black box.
--Pasted from my game changing brand recognized business phone
> To unsubscribe from this group, send email to cromemco+u...@googlegroups.com.
cory
Nov 14, 2012, 9:45:24 PM11/14/12
to Cromemco
Hi Martin,
It seems I was mistaken. I didn't have my probe correctly grounded. I
tested again (correctly) and the 24V post does supply 24.2V as
expected. There are 5 posts, +5V, COM, -5V, +24V, and the one I didn't
see before, "24V RET". to eliminate confusion I tested at the power
connector to the drive this time, and was getting the 24.2V there.
On Nov 14, 7:20 pm, Martin Eberhard <mfeberh...@gmail.com> wrote:
> Hi Cory,
>
> Yes, the caps on the 24v line are the ones that fail, and they fail to a short circuit :-(. This means that powering it up will probably do damage, and the more it is powered, the more damaged. Unfortunately, there is no fuse on the 24V supply.
>
> If you decide you want to sell it, please let me know- I am interested, and I am (think) one of the few remaining people who know how to get them running.
>
> Cheers,
> -Martin
>
> FYI,
> in the back of my napkin, I hope you’ve proactively fast tracked sufficient mission critical bandwidth to close the loop on leveraging global synergies ASAP up the flagpole. We’ll keep moving forward by encapsulating knowledge based best practice cookie cutter core asset skill set solutions in this collaboration task game plan thinking outside of the black box.
>
> --Pasted from my game changing brand recognized business phone
>
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