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Tandon floppy drive no longer wants to read any disks

tom.storey

tom.storey

Experienced Member
Joined
Nov 18, 2022
Messages
104
Location
London, UK
Hi all,

The Tandon drive in my XT was working (seemingly) beautifully up until I just tried it today. It has been probably several weeks since I last tried using it (Ive been plodding along nicely with the XT-IDE in the mean time).

In that time "that inductor" burned up along with "that capacitor" shorting out, although I cant quite remember if I tried the drive again after replacing those components, so I cant say for sure if they are related, but thats out there incase it matters.

Im wondering if anyone has any suggestions for troubleshooting steps to try to figure out whats going on. Ive given the heads a clean, and tried a fresh disk out of the pack, but no joy.

Attempting to read a disk in DOS gives me Abort, Retry, Fail, and attempting to format tells me that track 0 is bad on all disks that I try, including ones that I have previously formatted and had stored data on.

Any tips, links to troubleshooting guides etc appreciated. Thanks!
 
Could be radial alignment.

Do you have access to (1) a head-positioning utility, (2) an analog alignment disk to fit the drive, (3) an oscilloscope, and (4) the service manual for the drive?

Unfortunately, the last time I did a radial alignment on a floppy drive was sometime in 1986. Probably for an Apple //c. And I've forgotten more of the details of how to do it than 99.9999% of living human beings have ever known. All I can remember is that you hook up an oscilloscope to specified testpoints, load your head-positioning utility, insert the alignment disk, seek to track 16 (I think it's 16), loosen the stepper motor, and rock it back and forth until the "cat's eyes" are as close to equal size as possible.

Could also simply be a fried drive.

Since I haven't a clue what "that inductor" and "that capacitor" are, I have no way of knowing their side effects, but in that same period (working in the computer repair shop for the Los Angeles Unified School District), I also encountered floppy drives with fried boards.

In fact, I even encountered a bizarre Apple //c problem in which, because a non-polarized "Disk II" to "Unidisk" adapter was plugged in backwards on the "Disk II" side (to use a "Disk II" as an external drive), the internal drive of the //c got fried in such a way as to become incapable of distinguishing between read and write operations, causing it to write garbage to any non-write-protected disk it attempted to read. Never did understand how that could happen.
 
Sorry, I think this may be a false alarm. I installed a network card today, and having just removed that it seems everything is reading again.....

Going to have to check my settings!
 
Hmm maybe not. This is quite confusing and Im not sure whats going on.

Just now Ive tried removing the network card from the system while booting into my XT-IDE based DOS installation, and the floppys are not reading again.

It was working earlier when I booted into the DOS installation that was on the original MFM hard drive. I had the XT-IDE adapter in the system at that time as well.

Im not sure what the combination of hardware is that made it work. Is there some kind of reliance on the HDD adapter to make the floppy drive work?
 
My previously working MS DOS 3.3 boot disk (which I used to setup my XT-IDE based system) doesnt boot at all any more even with a bare bones system.

If I boot from the MFM HDD, I can, however, read it from the DOS installed on there (IBM DOS 3.1).

I formatted a floppy from there with the /s option, and I can boot from that disk whether the XT-IDE is installed or not, but still not the DOS 3.3 disk.

If I only have the XT-IDE card installed and remove the fixed disk card, I can boot the freshly made DOS 3.1 disk but not DOS 3.3. If I boot from the DOS 3.1 disk I cant access the C: on the XT-IDE card, and if I boot from the XT-IDE card I cant access even the freshly formatted DOS 3.1 floppy.

Its like one or the other haha.

I mean, I suppose its possible that these floppy disks being so old are starting to fade away already? If I can remember how I made them I might try re-making them and see if that changes anything.
 
tom.storey said:
My previously working MS DOS 3.3 boot disk (which I used to setup my XT-IDE based system) doesnt boot at all any more even with a bare bones system.
Click to expand...
Suspect: MS-DOS 3.3 boot floppy
Suspect: Floppy hardware

tom.storey said:
If I boot from the MFM HDD, I can, however, read it from the DOS installed on there (IBM DOS 3.1).
Click to expand...
Based on new information:
Suspect: MS-DOS 3.3 boot floppy (damaged boot code)
Suspect: Floppy hardware (something related to booting)

tom.storey said:
I formatted a floppy from there with the /s option, and I can boot from that disk whether the XT-IDE is installed or not, but still not the DOS 3.3 disk.
Click to expand...
Based on new information:
Suspect: MS-DOS 3.3 boot floppy (damaged boot code)
Suspect: Floppy hardware (head alignment affecting outer tracks?)

tom.storey said:
If I only have the XT-IDE card installed and remove the fixed disk card, I can boot the freshly made DOS 3.1 disk but not DOS 3.3.
Click to expand...
Same as previous.

tom.storey said:
If I boot from the DOS 3.1 disk I cant access the C: on the XT-IDE card, and if I boot from the XT-IDE card I cant access even the freshly formatted DOS 3.1 floppy.
Click to expand...
You could have multiple issues going on here.

If you start at basics, you should be able to boot a known-good DOS boot floppy with no hard drive controllers (XT-IDE or other) fitted.
Right now, the MS-DOS 3.3 boot floppy is suspect and if so, is confusing the matter.
Eliminate it - can you boot from it in other computer (one where the floppy drive is known good, including head alignment)?

tom.storey said:
If I boot from the DOS 3.1 disk I cant access the C: on the XT-IDE card, and if I boot from the XT-IDE card I cant access even the freshly formatted DOS 3.1 floppy.
Click to expand...
So here, the suspect MS-DOS 3.3 boot floppy is 'out of the equation'. Good.

But I am puzzled by this particular symptom. You used "bare bones" before. Confirm that for this particular symptom, the only cards fitted are video + floppy controller + XT-IDE.
And what I/O base port is the XT-IDE set for?
 
My bare bones setup was video, floppy, and the async card in slot 8 which I left in as I cant imagine that having anything to do with it. I can try with it out as well if needs must, but it was just one less thing to take out.

Unfortunately this is the only machine I have access to, and no one in my immediate circle is in to this kind of thing either, so Im not able to test disks in anything else unless I went to some kind of retro computing museum or such.

XT-IDE base address is set for 0x380.

Earlier on when I suspected it might have been the network card I had it set at 0x320 which clashes with the fixed disk controller, but I have now moved it up to 0x360 which seems to be address space set aside for network adapters.

Something I forgot to mention before, when I try to boot the DOS 3.3 disk with the XT-IDE adapter I get an error 4C and then it falls back to booting from CF.
 
tom.storey said:
My bare bones setup was video, floppy, and the async card in slot 8 which I left in as I cant imagine that having anything to do with it. I can try with it out as well if needs must, but it was just one less thing to take out.
Click to expand...
Of course, even though you cannot think of any possibility, doesn't mean that a possibility doesn't exist. And that possibility might be highly unlikely, but people do win the lottery. You really should remove the card, just to be sure.

tom.storey said:
Unfortunately this is the only machine I have access to, and no one in my immediate circle is in to this kind of thing either, so Im not able to test disks in anything else unless I went to some kind of retro computing museum or such.
Click to expand...
That is unfortunate. I have multiple machines, disks, and spares, which makes diagnosis much easier.

tom.storey said:
If I boot from the DOS 3.1 disk I cant access the C: on the XT-IDE card, and if I boot from the XT-IDE card I cant access even the freshly formatted DOS 3.1 floppy.
Click to expand...
Earlier, I was thinking to myself, "What is going on there? It is the same version of DOS on both media." But in re-reading the thread, I see that DOS 3.1 is on the MFM HDD. What version do you have on the XT-IDE ?
 
Another experiment to try is {only cards = video + floppy controller + MFM controller}
If that shows no floppy problems, and {only cards = video + floppy controller + XT-IDE} does, then that points the finger at the XT-IDE.
 
modem7 said:
I wonder if there was a computer virus that played tricks like this.
Click to expand...
Some time back my 5160 got infected with the 'Stoned' virus, I got it from some old 720k floppy disc's i had from many years ago, It left me scratching my head for a day or so because i couldn't figure out why perfectly working floppy disc's were no longer booting etc, It wasn't until i checked for a virus that i found out why.
 
If this is indeed some boot virus infection causing unreadable disks , then if you could find a way to run my portable antivirus in your machine, it can definitely get rid of that boot sector virus like Stoned, Michelangelo, etc.. no need to boot from clean disk as it can disable the virus even if it's active in memory, unfortunately it only runs on .286 and up
 

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Well, Im not really sure what to make of this.

I grabbed the installation disks for DOS 5.0 and wrote them to a set of floppys using IMD - from DOS 3.3 running on the XT-IDE. It seems it could write disks just fine..?

I then installed DOS 5.0 onto a new CF card from those floppys.

Under DOS 5.0 I was not able to read the DOS 3.3 floppys, nor could they be booted. XT-IDE gives an error code 4h (I think I mentioned 4C above) before booting from the C drive.

Under DOS 5.0 I was able to format the DOS 3.3 floppys and read them just fine.

I did also try removing *everything* except video, floppy controller and XT-IDE, and still it wasnt able to boot the DOS 3.3 disks.

So I dont really know what to do. Did I get some kind of virus? I suppose thats possible since I downloaded a couple of bits and bobs from here and there and who knows whats floating around in those....

Is it worth trying to troubleshoot this further? I dont know that either. Right now its all working enough that Im happy with it I guess.

The biggest issue I have now is that, for some reason, when I have my home made "RAM expansion+other things card" installed I cant boot the DOS 5.0 floppy. The drive makes a "machine gun" type noise, so I guess its trying to extend beyond its reach for some reason. Not sure what is up with that, but if I remove the card it boots perfectly fine... It can always boot off the XT-IDE though.

Crikey lol.

Oh, and in case it was something to do with where I have configured all of my peripherals and what not, I tried moving the XT-IDE adapter down to 0x220, and moved the things on my home made card down into the 0x1XX area as well as disabling the peripherals on-board, and that still made no difference.

I guess it might be interesting to see if after a couple more weeks the DOS 5 disks that I have created are still functional... I'll try to remember to post an update about that.
 
Last edited:
The XT is my only machine, so if anyone has any suggestions for an antivirus I could grab, then I suppose that may be worthwhile. The machine originally came with a copy of McAfee, who knows what version, and that didnt seem to pick anything up, but it only had something like 67 viruses in its database apparently, so yeah....
 
tom.storey said:
The XT is my only machine, so if anyone has any suggestions for an antivirus I could grab, then I suppose that may be worthwhile.
Click to expand...
I see:

F-PROT
"free to use for non-commercial purposes."
The last version of F-prot which works with 8088/8086 is version 2.27a (July 1997) with the latest definitions of 1997.
 
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