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View Full Version : Difficulty with 8" Drives, Need Expert Advise Please



marmotking
December 4th, 2008, 07:02 PM
I have a pile of 8" floppy disks, which I'd like to image and archive. I know that some are for a PDP-11/23 RX02 drive and some are for the TRS-80 Model II. Still others are for a Heathkit H11 and H27 drive. What I've done is obtained an 8" converter from dbit.com so that I can plug an 8" drive into my Catweasel MK4, which can be used to image the disks. There's a utility written by Tim Mann (see www.tim-mann.org/catweasel.html for cw2dmk.exe) which can read all of these formats, I believe.

So, here's the problem. I managed to make a good boot floppy from a DMK that's also on his site for a Model II. But, I can't seem to do it anymore after that first one. I write the image using dmk2cw.exe. It appears to go correctly. Then I try to read it back using cw2dmk.exe. The problem is, that when it hits about track 60, I start getting all sorts of bad sector reads. The first few read back sucessfully with lots of retries, but the rest just give lots of errors.

Now, I admit to not knowing anything about 8" drives and media. I've tried several drives (all Tandon tm-848 drives), which I believe to be double sided double density. I'm using floppy disks labeled, soft sector, single head, single side, single density, 26 sectors/128 bytes. It's got an index hole almost directly over the center ring, but ever so slightly to the right.

I've tried multiple power supplies for the external drive. I've tried multiple media. I can't seem to make an image that will read back properly. I did manage this once, in that I made a disk and was able to boot a TRS-80 Model II from it. (see LS-DOS image on Tim Mann's site).

Any advise? I've got a pile of borrowed disks with a nurvous owner, but would like to image these. Time's running out for me to get this all working. Any help would be GREATLY appreciated! Please ask me questions...

Druid6900
December 4th, 2008, 08:10 PM
Well, the only thing that seems common is the DMK file that you downloaded.

Try getting another image and trying that.

Chuck(G)
December 4th, 2008, 09:18 PM
Are you asserting TG43 when you're writing tracks higher than 43? (I'm assuming that your drive is one that requires it). This reduces the write current and enables the inner tracks to be recorded without getting "blurred".

DBIT has an adaptor with a PIC on it that tracks the head position and asserts TG43 automatically. A neat little widget--and inexpensive.

Micom 2000
December 4th, 2008, 10:08 PM
I don't know if this won't just muddle your problem but I have a Model II and back in the early 90s a very experienced M-II guy suggested that I should copy all my 8" disks to 5.25" floppies because 8" fdd's and floppies were becoming scarce and I could use a 5.25 fdd with the proper cable on the M-II. Possibly the Catweasle could be used to facilitate copying.
That way you could copy your nervous owners disks to 5.25 floppies, return the disks, and archive them later at your leasure.

There's a link on Tim Mann's site to a bunch of Don Maislin's notes on the subject. I never did do the transfer myself but all it requires is a cable and/or possibly the adaptor your using on the Cat would suffice. The speed of 8" and 5.25" FDDs is almost identical.

Lawrence

Lou - N2MIY
December 5th, 2008, 02:59 AM
From all that I've read, you will not be able to read the RX02 floppies on a PC. There is mixed single and double density encoding within a single track. RX01s however, are all single density. I have an SA860 connected to the motherboard floppy controller of an IBM PC300 and can only read RX01s. I would be pleasantly suprised if the catweasel can support RX02.

For RX02s, I read them on drives connected to real 11/23s and an 8/e.

I can help you read the RX02s on real hardware if you are intersted. If they are RT-11 format, I know for certain I can transfer the contents for you.

Lou

Chuck(G)
December 5th, 2008, 08:52 AM
From all that I've read, you will not be able to read the RX02 floppies on a PC. There is mixed single and double density encoding within a single track. RX01s however, are all single density. I have an SA860 connected to the motherboard floppy controller of an IBM PC300 and can only read RX01s. I would be pleasantly suprised if the catweasel can support RX02.

He's using a Catweasel--a sampling controller. I've read and copied RX02 "weird MFM" as well as many other "non-PC-able" formats, such as GCR and MMFM using one. The CW records domain transitions and leaves the rest to software.

His problem is probably not asserting TG43/RWC when he's writing inner tracks.

nige the hippy
December 5th, 2008, 09:48 AM
I've heard that only certain media is susceptible to bleed-over of the bits, and that manually selecting the TG43 (or not) will work for most disks, but then I'm not reading the first post carefully enough (re-read it Chuck!). That's already taken care of.

It's not something as daft as a dirty head picked up from the first disk is it?

Also if it's a belt driven floppy, check out the drive belt. If the drive's been sat for a while, it could be slack or have a bit of a kink in it where it was sat round the motor pulley.

Chuck(G)
December 5th, 2008, 12:02 PM
Nige, I've seen the same thing with RX02s--without TG43, some seem to be more sensitive to the bit crowding on the inner tracks. Probably the formulation and particle size, more than anything.

FWIW, I never could get an RX02 to copy onto a silver-boxed Radio Shack 8" floppy, whoever made it. I tend to stick with NOS Dysan media when I can get it.

A quick check with one of the CW utilities will tell you if the spindle's spinning at the right speed. And you're right--dirty heads are another issue, but my own experience with RX02s and the CW would point in a different direction, as he can read the RX02s just fine, it seems.

Dwight Elvey
December 6th, 2008, 06:56 AM
Nige, I've seen the same thing with RX02s--without TG43, some seem to be more sensitive to the bit crowding on the inner tracks. Probably the formulation and particle size, more than anything.

FWIW, I never could get an RX02 to copy onto a silver-boxed Radio Shack 8" floppy, whoever made it. I tend to stick with NOS Dysan media when I can get it.

A quick check with one of the CW utilities will tell you if the spindle's spinning at the right speed. And you're right--dirty heads are another issue, but my own experience with RX02s and the CW would point in a different direction, as he can read the RX02s just fine, it seems.

Does the Catweasle support tg43? If not, one could
use a manual switch and switch it when close to track
43. Plus or minus a few tracks won't make much difference.
Dwight

Chuck(G)
December 6th, 2008, 08:27 AM
Does the Catweasle support tg43? If not, one could
use a manual switch and switch it when close to track
43. Plus or minus a few tracks won't make much difference.
Dwight

I'm not sure if this holds for all models of Catweasel, but other than the pin 2 density select bit, I don't believe that there are any extra programmable bits. One could, I suppose, connect the line to a switch as you suggest, or even run it off of a spare parallel port.

But I think the DBIT cable adapter is a very clever bit of off-the-shelf technology. One could make one's own version using one of the 6 or 8-pin uCs; the logic is insanely simple. I've wondered if it's possible to do this board without requiring an external power source--surely there's enough power available from the pullups on the host and drive sides to steal a milliamp or two.

Since the OP doesn't start to see errors until around cylinder 60 or so, he might try manually grounding TG43 one time to see if that makes a difference.