Reconstructing an AT&T 7300

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vla...@gmail.com

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Jun 11, 2015, 8:38:55 AM6/11/15
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Hello All,

I've found an at&t 7300 and disconnected floppy, hdd and display. When I power it up relays in modem are going crazy.

Why the relays are going crazy?

Thank you

DoN. Nichols

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Jun 11, 2015, 8:14:55 PM6/11/15
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Well ... it is most likely the connector on the power supply.
You already have it apart, if you have all of those disconnected, so you
can look easily.

Pull the wide single-row connector (orange plastic) from the row
of pins on the power supply. Look along its side. If any of the
plastic over the pins has turned slightly brown, it has developed high
resistance and is heating, and the voltage is spiking and falling.

If it is *very* brown, or black, it has probably heated things
up badly enough so the solder has melted from around one of the pins on
the underside the power supply's circuit board. (You'll have to pull
the power supply out of the system to verify this, and to work on it.)

Since it is a 7300, not a 3B1, I suspect that the power for the
hard disk drive is fed through the system board, so it burns the
connector a bit sooner. (Later 3B1 power supplies have a cable soldered
directly to the board to carry power to the hard disk drive, and thus
reduce the current through the rest, though it also typically has a full
2MB of RAM on the system board, so the current load there increases.

If the connector is dark brown from overheating, it really
should be replaced. It is possible to pull the back cover off it, then
ease the indivdual wires from the stiff ribbon cable out of the
individual slots, and install them in a replacement connector of the
same type by pressing down on either side of the metal of each pin, with
perhaps the tips of some needle-nose pliers.

IIRC, the connector has either 18 pins or 38 pins -- I forget
which.

But, in any case, spray the pins with a good contact cleaner,
and slide the connector on and off the pins several times to clean off
any oxidation. What I use to really like was something called
"Cramolin", but it got discontinued because of something toxic or bad
for the ozone layer, and it was replaced with something called De-Oxit.

Either of them come in two colors, intended to encourage you to
spray with one, wipe it clean, and then spray again prior to
reassembling.

Of course, it could be something else, but this is what I would
check first.

Good Luck,
DoN.

--
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Email: <BPdnic...@d-and-d.com> | (KV4PH) Voice (all times): (703) 938-4564
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--- Black Holes are where God is dividing by zero ---

Convergent MightyFrame

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Jun 13, 2015, 2:46:54 PM6/13/15
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DoN here always has excellent suggestions. He's helped me through a lot of problems.

I have restored several of these machines myself, and am working on yet another.

If you like, I'd be open to a Skype session or Google Hangout sometime to help you through any issues that I can. I like to see people restore vintage UNIX things like this. It has become a hobby of mine in recent years.

Drop me an email at mighty...@gmail.com

Or visit my stie at

http://MightyFrame.com

All the best,
-AJ

vla...@gmail.com

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Jun 15, 2015, 2:01:31 PM6/15/15
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Thank you.
I've replaced power supply with a pc atx power supply. Relays are normal now.
I'm trying to boot at&t, but i see only running green rectangles. All 4 leds are on.
Lithium battery is dead.

I will try to replace battery. I think it will solve boot problem.


vla...@gmail.com

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Jun 15, 2015, 2:01:47 PM6/15/15
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Thank you

DoN. Nichols

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Jun 16, 2015, 9:45:07 PM6/16/15
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On 2015-06-15, vla...@gmail.com <vla...@gmail.com> wrote:
> On Friday, June 12, 2015 at 3:14:55 AM UTC+3, DoN. Nichols wrote:
>> On 2015-06-11, vla...@gmail.com <vla...@gmail.com> wrote:
>> > Hello All,
>>
>> > I've found an at&t 7300 and disconnected floppy, hdd and display. When
>> > I power it up relays in modem are going crazy.
>> >
>> > Why the relays are going crazy?
>>
>> Well ... it is most likely the connector on the power supply.
>> You already have it apart, if you have all of those disconnected, so you
>> can look easily.

[ ... ]

>> Of course, it could be something else, but this is what I would
>> check first.

[ ... ]

> Thank you.
> I've replaced power supply with a pc atx power supply. Relays are normal now.

O.K. So likely the power supply connector and/or pins. (Did you
bother to look at the underside of the power supply for melted away
solder around the pins? Also look for "cold solder" joints -- the
solder looks frosted instead of shiny. If you see that, remove as much
solder as you can from that junction and then flow fresh 63/37 lead-tin
solder to get a clean smooth joint.

> I'm trying to boot at&t, but i see only running green rectangles. All 4 leds are on.
> Lithium battery is dead.
>
> I will try to replace battery. I think it will solve boot problem.

The only difference that will make will be that if you manage to
get it to boot twice, it will remember the date from the first boot.
That cell does *nothing* else than run the clock chip.

So -- the marching squares usually come from the inability to
find a boot image on either the hard disk or the floppy. Are you trying
to boot from the hard drive? If it was in there while the system was
getting very glitchy power, as evidenced by the relays, it is almost
certainly not bootable now, and will need to be reformatted and
reinstalled.

Do you have the floppy set for installing the OS? There is the
basic set, and the development set as an extra-cost option, which gives
you things like compilers, a somewhat better default editor (vi/ex
instead of ed) and a number of other things. There is a floppy set in
the original set which handles encryption, and happens to include a
version of vi/ex which includes encryption. It first checks for the
presence of an installed vi, and updates that if so -- otherwise it
skips it. This means that if you want the updated vi/ex, you must
install the development set before installing the encryption set. (The
encryption was separate, because it could not be exported back then. :-)

vla...@gmail.com

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Jun 17, 2015, 3:18:19 AM6/17/15
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I don't have a floppy set. There are images here(http://bitsavers.trailing-edge.com/bits/ATT/unixPC/). Can i use it?

if so can i attach floppy disk from at&t to old PC?
Can i use dd to put *.IMD file to floppy?

Thank you

DoN. Nichols

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Jun 17, 2015, 11:42:53 PM6/17/15
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On 2015-06-17, vla...@gmail.com <vla...@gmail.com> wrote:
> On Wednesday, June 17, 2015 at 4:45:07 AM UTC+3, DoN. Nichols wrote:

[ ... ]

>> So -- the marching squares usually come from the inability to
>> find a boot image on either the hard disk or the floppy. Are you trying
>> to boot from the hard drive? If it was in there while the system was
>> getting very glitchy power, as evidenced by the relays, it is almost
>> certainly not bootable now, and will need to be reformatted and
>> reinstalled.
>>
>> Do you have the floppy set for installing the OS? There is the
>> basic set, and the development set as an extra-cost option, which gives
>> you things like compilers, a somewhat better default editor (vi/ex
>> instead of ed) and a number of other things. There is a floppy set in
>> the original set which handles encryption, and happens to include a
>> version of vi/ex which includes encryption. It first checks for the
>> presence of an installed vi, and updates that if so -- otherwise it
>> skips it. This means that if you want the updated vi/ex, you must
>> install the development set before installing the encryption set. (The
>> encryption was separate, because it could not be exported back then. :-)

> I don't have a floppy set. There are images
> here(http://bitsavers.trailing-edge.com/bits/ATT/unixPC/). Can i use it?

Yes -- with some way to get the data onto the floppies.

IIRC, there is a program on there to properly format and copy to
floppies in a PC -- though I'm not sure how old a PC it may have to be.

> if so can i attach floppy disk from at&t to old PC?

IIRC, that drive had weird jumpering, and it would probably not
work. I remember making some 3.5" drives work, doubling the capacity of
a single floppy -- but not all the way to the 1.4 MB of a HD floppy.

> Can i use dd to put *.IMD file to floppy?

I don't think so. Those require the speical programs which
should be there -- imd117.zip or imd117sc.zip.

Here is part of the "README.TXT" file which accompanies the
images:


======================================================================
ImageDisk
---------
ImageDisk is a program to read entire diskette images into files (type .IMD),
and to recreate a copy of the diskette from that image. A detailed analysis
is performed on the diskette, and information about the formatting is recorded
in the image file. This allows ImageDisk to work with virtually any soft-
sectored diskette format that is compatible with the PC's type 765 floppy
diskette controller and drives.
======================================================================

one of the zip files ha a number of .Com and .Exe files, and the other a
number of .C source files. I forget whether the .C files compile on a
PC or a linux/unix box.

And looking at the head of a typical .IMD file, I doubt that it
could be copied directly onto a floppy. Though perhaps dd could be used
to skip just enough of the first part, if the rest is a true floppy
image. I just don't know. Best to find an old PC with a 5.25" floppy
drive.

vla...@gmail.com

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Jun 25, 2015, 4:44:05 AM6/25/15
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I have successfully attached at&t's floppy drive(TEAC FD-55b-01-U) to my PC (Pentium 4). I can use floppy drive in DOS. I had to put 2 floppy drives in order to use at&t's floppy drive. Drive A - 3.5 floppy drive and Drive B - at&t's floppy drive. I've replaced jumper on at&t's floppy drive from ds0 to ds1.

I've restored floppy disks from IMD files using imd118 utility in DOS.

I want to test this disks. I put disk in at&t's floppy drive and try to boot it. But floppy drive don't even try to read it.

How to force at&t to boot from floppy disk?

Thank you

DoN. Nichols

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Jun 25, 2015, 10:23:41 PM6/25/15
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On 2015-06-25, vla...@gmail.com <vla...@gmail.com> wrote:
> On Thursday, June 18, 2015 at 6:42:53 AM UTC+3, DoN. Nichols wrote:
>> On 2015-06-17, vla...@gmail.com <vla...@gmail.com> wrote:

[ ... ]

>> > if so can i attach floppy disk from at&t to old PC?
>>
>> IIRC, that drive had weird jumpering, and it would probably not
>> work. I remember making some 3.5" drives work, doubling the capacity of
>> a single floppy -- but not all the way to the 1.4 MB of a HD floppy.

> I have successfully attached at&t's floppy drive(TEAC FD-55b-01-U) to
> my PC (Pentium 4). I can use floppy drive in DOS. I had to put 2 floppy
> drives in order to use at&t's floppy drive. Drive A - 3.5 floppy drive
> and Drive B - at&t's floppy drive. I've replaced jumper on at&t's floppy
> drive from ds0 to ds1.

> I've restored floppy disks from IMD files using imd118 utility in DOS.

> I want to test this disks. I put disk in at&t's floppy drive and try
> to boot it. But floppy drive don't even try to read it.

Did you remember to set the drive jumper back to where it was?

I'm not sure, but I seem to remember that the jumper was set to
DS3 not DS0 -- you will have to try both to be sure. At one time I
modified one 3B1 so it had a choice of three floppy drives:

Standard 400K 5.25" floppy
Rare 800K 5.25" floppy (not HD)
3.5" floppy (re-jumpered to be 800K instead of 1.4 MB.

No point in trying the HD drives, as the floppy controller, and
the software driving it, could not access them, even with the right
drives. :-)

I took the drive select signal (whichever one it really was) and
used a rotary switch to redirect it to one of the other three DS wires
in the ribbon cable.

It took a little work on the files which define the formats, but
the modified file worked on both the 800K drives. I even set up a set
of duplicates for all the install floppies re-packed to fit the 3.5"
floppies.

If you can go back through the archives of comp.sys.3b1, you
should find my description of that while it was still fesh in my mind. :-)

Never had a chance to use them, before the systems were retired.
Not sure whether they are still readable. But essentially, I used cpio
to get all the floppies from a given set into a subdirectory of /tmp,
and then used cpio again to re-write them to fewer 3.5" floppies. It
also made for a diagnostic floppy with more room for fixing things.

BTW -- You know that the only bootable floppy in the set is the diagonstic
one? And somewhere in that one is the table of formats for hard
disks and floppy disks which has to be modified to use larger
drives.

vla...@gmail.com

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Jul 7, 2015, 4:24:48 AM7/7/15
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I have successfully booted from diagnostic floppy.
I have got st-251-0 HDD. I can't format this disk(error: Can't write the new VHB : Response = 10).

But i can successfully low format this st-251-0 on 286 PC(WD1003-WA2 ISA board) with seagate disk utility 3.0.
And i can run DOS 3.3 from this HDD.

I have put jumper DS0 on HDD.

HDD parameters:
# of Cylinders: 820
# of Tracks per Cylinder: 6
# of Sectors per Track: 17

DoN. Nichols

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Jul 11, 2015, 9:06:01 PM7/11/15
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On 2015-07-07, vla...@gmail.com <vla...@gmail.com> wrote:
> I have successfully booted from diagnostic floppy.

Congratulations on your progress.

> I have got st-251-0 HDD. I can't format this disk(error: Can't write
> the new VHB : Response = 10).

I don't know the specific meaning of 10 as an error code. It
might be in the WD1010 HD controller chip, or it may be in the driver in
the kernel.

> But i can successfully low format this st-251-0 on 286 PC(WD1003-WA2
> ISA board) with seagate disk utility 3.0.

O.K. The disk works, at least. Did you find an entry for that
disk in the diagnostic floppy? If not -- perhaps try the alternate
diagnostic floppy, which is used with a newer kernel and with systems
which have been modified to access a second hard drive. IIRC, it has a
larger list of hard disks -- as well as the possibility of entering the
disk parameters manually.

> And i can run DOS 3.3 from this HDD.
>
> I have put jumper DS0 on HDD.
>
> HDD parameters:
> # of Cylinders: 820
> # of Tracks per Cylinder: 6
> # of Sectors per Track: 17

You'll get less space on the 3B1/7300/Unix-PC. It reserves one
sector at the end of each track for a replacement when a nearby sector
goes bad. (Happened a lot in those days.)

vla...@gmail.com

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Jul 15, 2015, 10:46:12 AM7/15/15
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Where can i find the image of alternate diagnostic disk?

Thank you

DoN. Nichols

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Jul 17, 2015, 11:53:08 PM7/17/15
to
On 2015-07-15, vla...@gmail.com <vla...@gmail.com> wrote:
> On Sunday, July 12, 2015 at 3:06:01 AM UTC+2, DoN. Nichols wrote:
>> On 2015-07-07, vla...@gmail.com <vla...@gmail.com> wrote:
>> > I have successfully booted from diagnostic floppy.
>>
>> Congratulations on your progress.

[ ... ]

>> O.K. The disk works, at least. Did you find an entry for that
>> disk in the diagnostic floppy? If not -- perhaps try the alternate
>> diagnostic floppy, which is used with a newer kernel and with systems
>> which have been modified to access a second hard drive. IIRC, it has a
>> larger list of hard disks -- as well as the possibility of entering the
>> disk parameters manually.

[ ... ]

> Where can i find the image of alternate diagnostic disk?

Well ... where did you download the images of the Foundation
set? The first disk of that is named: "01of12a-Std-Diag" in at least
one copy that I have, and right after that is: "01of12b-Enhanced-Diag".

So -- what you want to do is look for the "enhanced diagnostic"
disk and substitute it for the stanrad diagnostic disk.

My first hit doing a search for:

3B1 7300 Unix-PC enhanced diagnostics

(using DuckDuckGo as my preferred search engine) was

AT&T 3B1/7300 (UNIX PC) information, and a bit of searching
through that leads me to:

<http://unixpc.taronga.com/kernel/>

where you find (among other things):

======================================================================
kernel/s4diag.cpio.gz (91/10/12)
Enhanced version of the UNIXpc diagnostic program that permits
formatting hard disks with > 8 heads and/or > 1024 cylinders.
======================================================================

You also want to get from that same directory:

======================================================================
kernel/s4test.info (91/10/12)
Documents the various "s4test" expert-mode diagnostic routines
accessible through the UNIXpc diagnostic disk.
======================================================================

So -- that is what I was talking about.

Various other things of possible interest there, too.

vla...@gmail.com

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Aug 4, 2015, 7:36:50 AM8/4/15
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I have found st-412 HDD. I can use it with WD MFM controller. I can run DOS 3.3 on it.
When i put it to at&t i got the same error -" Error : WINCHESTER:Can't Write the new VHB:Response = 10".
So i have got 2 HDD. I can run DOS from them and have the same errors in at&t.
Maybe the source of errors is at&t?

DoN. Nichols

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Aug 8, 2015, 10:11:27 PM8/8/15
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Yes -- or the cables from the computer to the drive.

There should be two ribbon cables and the power cable.

One ribbon cable is 34 conductors wide

The other is 20 (IIRC).

Both are sensitive as to which end of the connector is on which
end of the corresponding connector on the drive.

Look for either a small triangle (or the number '1') adjacent to
a corner pin -- or for a square pad on one pin at one corner. The
colored stripe on the ribbon cable should go to this end in both cases.

If the system has been modified to accept larger drives or a
second drive, there will be a second narrow cable, and a second
connector on rhe wide cable to connect to the control/status logic of the
second drive.

If this is all correct (you could swap the cables between
computers for a test to see that they are good), then the next most
likely things are the controller chip (WD1010 by default, WD2010 if the
system has been modified to handle drives with more than eight heads,
or more than 1024 cylinders -- or a second hard drive).

There are also the driver and receiver chips to send and receive
balanced read/write data to/from the disk drive.

If you have the maintenance manual (you can download and print
it now, I believe) you can look up which chips serve the driver and
receiver functions.

vla...@gmail.com

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Dec 13, 2021, 5:00:15 PM12/13/21
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Finally i solved my problem with MFM hard drive error (Can't write the new VHB : Response = 10)

I got my hands on logic analyzer and good motherboard from unixpc (0.5MB version). I started poking around probes on two motherboards. I realized that the output clock signal from VCO chip 14N pin11 was 5MHz instead of 10MHz and 14N pin 1 was 1 volt instead of 2 volts.

Long story short - the problem was opamp 17N (LF412). I changed it with LF412CN.

Now i can boot from mfm disk.
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