[Coco] CoCo Disk Drives

[Gene Heskett]

On Friday 27 February 2015 14:34:40 Rick Thornquist wrote:
> Al and Gene -
>
> All right, I opened the drives up.  Even though they have different catalog
> numbers, they appear to be pretty much identical on the inside (then again,
> the catalog number on the 26-1164 is on a sticker over the previous one -
> I'll have to see what's under there someday).  Even the drive mechanism -
> Texas Peripherals (10-5355-001) - is the same.  Texas Peripherals?  Hmm...
> Doesn't sound quite legit. :)
>
Oh its legit, but not that great a drive either.  Somewhat early shall we say?

> Anyway, here's a picture of the logic board of the 26-3029:
>
> https://dl.dropboxusercontent.com/u/18477511/26-3029%20Logic%20Board.jpg
>
> There doesn't appear to be any DIP switches or jumpers for drive select,
> instead there appear to be four drive select lines in the bottom right or
> the logic board - DS 1 2 3 4.  I guess they expect you to do the drive
> selection with a pulled pin cable.  Fine with me.

In your case, you should be reading with an ohmeter, infinity (open, no 
connection, from DS1-3,4 to anything else on the board. Drives are addressed 
in base0 numbering, but the DS labels often start at DS1 and go to 3, so 
subtract one from those to get the drives number, eg DS-2 is drive one, and 
should be the only pin with continuity to anything else.

> As far as the termination pack is concerned, I'm thinking that it's R51,
> right above the drive select lines.  It has six pins.  Please correct me if
> I'm wrong!  Both drives have this pack so it seems like I have to remove
> one of them.

Yes, that is it I believe, so remove it from the drive in the middle of the 
cable.

> Here's the thing.  The pulled pin cable is set for drive 0 in the middle of
> the cable and drive 1 at the end.  You all are saying that the termination
> pack should only in the drive at the end of the cable, so that will be
> drive 1.   That also sound good, but Service Manual that I found says on
> page 5 (page 8 of the PDF), "The Resistor TerminatIon in the IC socket is
> used in Drive number zero only. It must be removed for Drives one. two and
> three."  But my drive 0 is in the middle of the cable!

It's sorta machs nichs, you could interchange the drives, and run the cable in 
from the other side.  that would still leave the drives at their current 
assignments but with zero on the end of the cable I think.  But I doubt it 
will make any diff except in the clarity of how you understand it. :)

Another point to be made is how well lubricated are the rails the head 
carriage slides in and out on, and on the TP drives how clean and undamaged 
is the grove in the spiral disk that actually moves the heads in and out as 
it rotates a few degrees to move the head.  That is dirt sensitive, and often 
not well lubed because the lube attracts dirt and the dirt accelerates the 
wear rate of the grooves. But all that needs to be well cleaned, and relubed 
with a light oil.  Fairly often, as in annually or quicker on those drives.

Those TP drives also should not be driven at more than the default 30ms/step 
step rate as the disk itself is a flywheel that does not exist in other head 
drive schemes the later drives use.  If the step drivers do not use an 
accel/decel speed profile, and I have yet to see a computer controller that 
did, the attainable step rate is limited by how fast you can drive it, and 
stop it on the next track.  There is no run to track 33 , but continuous, 
timed, single step at a time until it gets there.

My lathe and milling machines can do a minimum of 20 times that single step 
speed by using suitable acceleration and deceleration profiles. And still has 
enough power to snap off a $20 1/4" diameter carbide cutting tool if it does 
hit something at those speeds. :(

> Here's the Service Manual:
>
> https://dl.dropboxusercontent.com/u/18477511/Radio%20Shack%20Mini%20Disk%20
>Service%20Manual.pdf
>
> So, where should the terminator be, on drive 0 (like the manual says) or
> drive 1 (at the end of the cable)?

Which ever is physically on the end of the cable.

> - Rick
>
> On Fri, Feb 27, 2015 at 12:05 PM, Gene Heskett <gheskett at wdtv.com> wrote:
> > On Friday 27 February 2015 09:21:00 Rick Thornquist wrote:
> > > Since you guys were so great answering my previous question, I have
> >
> > another
> >
> > > for you.
> > >
> > > When I acquired my CoCo 3, I got a 26-3029 controller and two disk
> >
> > drives,
> >
> > > a 26-3029 and a 26-1164.  I didn't get any manuals, so I just connected
> > > them up in what looked to be the right way.  I have the 26-3029
> > > connected to the middle of the floppy cable (as drive 0), and the
> > > 26-1164 connected to the end of the cable (as drive 1).  The setup does
> > > work for the most part, but there is some flakiness, mainly with the
> > > 26-1164.
> > >
> > > My question: Is there some configuration, like with drive select dip
> > > switches or terminators, that I'm supposed to do?  Also, my Internet
> > > digging suggests that the 26-1164 is a TRS-80 disk drive - is it also
> > > supposed to work with the CoCo?  .
> > >
> > > Thanks!
> > >
> > > - Rick
> >
> > Two things to pay attention to, Rick.
> >
> > 1. Only the drive connected at the end of the cable is supposed to have
> > resistor packs installed to terminate the lines.  If both have them
> > installed, thats too much of a load on the controller.  If none are
> > installed
> > (empty 8 or 9 pin inline sockets) then you have to find a set and install
> > them
> > on the end drives pcb.
> >
> > 2. Generally speaking, MOST of these drives have a means of selecting
> > which drive address they respond to, and because the default cable
> > supplied by the
> > shack actually does that with missing "teeth" in the edge connectors on
> > the cable, and intend that the drive on the end of the cable is drive 0,
> > I usually ditch those connectors and crimp on 34 pin card edge socket
> > connectors that are fully populated so you can actually make use of the
> > DS jumpers on the drives board, s/b 4 choices in 5.25" drives but only 2
> > on the
> > 3.5"ers. One and only 1 position is jumpered in this case.
> >
> > However you jumper them, its the end of the cable drive only that needs
> > the terminations installed.
> >
> > No clue what the 26-1164 drive is, single head or double sided heads, but
> > its
> > likely that at that age, completely usable on the coco's, at least with
> > os9/nitros9 when the descriptor is configured to match what the drive can
> > do.
> >
> > Cheers, Gene Heskett
> > --
> > "There are four boxes to be used in defense of liberty:
> >  soap, ballot, jury, and ammo. Please use in that order."
> > -Ed Howdershelt (Author)
> > Genes Web page <http://geneslinuxbox.net:6309/gene>
> >
> > --
> > Coco mailing list
> > Coco at maltedmedia.com
> > https://pairlist5.pair.net/mailman/listinfo/coco

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>