BBC Master 128

[G3PIJpeter]

I have a working BBC Master under the usual Watford twin disk drives in a plinth and RGB monitor on top. I have fitted new batteries and input all the Configure lines required.
The startup screen is as it always was but my floppies refuse to load under the usual *ADFS command - all I get is 'Disc fault 18 at 0: 00/00'. When fired up a few years ago, I used to get this message with some of the disks but not all.
Have they all now gone corrupt due to the earth's magnetic field - or what? Can I fix this fault? All suggestions (in 'idiot's guide' language) gratefully received.
- Peter

[electronicskip]

not sure if im allowed to post this,(apologies if its wrong)
this might help
http://www.stardot.org.uk/forums/vie...php?f=3&t=4661

[SiriusHardware]

Looking at one of the non-working discs, does the surface you can see through the head slot look OK? Uniform colour? Not mouldy?

If you have one spare disc, try formatting it, saving a file to it and reading it back. If that works OK, then unfortunately your other discs may have gone bad.

I had a box full of Sinclair Spectrum microdrive cartridges which were all stored working, but when tried them again about 20 years later only one or two of twenty were readable, despite their all looking physically OK.

[G3PIJpeter]

Originally Posted by SiriusHardware

Looking at one of the non-working discs, does the surface you can see through the head slot look OK? Uniform colour? Not mouldy?

No - they all look fine. They have been stored for 15+ years in my brick shed but it does have heating and a dehumidifier.

Originally Posted by SiriusHardware

If you have one spare disc, try formatting it, saving a file to it and reading it back. If that works OK, then unfortunately your other discs may have gone bad.

That is the obvious think to do - thanks for the suggestion.I shall give it a go tomorrow and report back.

Originally Posted by SiriusHardware

I had a box full of Sinclair Spectrum microdrive cartridges which were all stored working, but when tried them again about 20 years later only one or two of twenty were readable, despite their all looking physically OK.

It looks like I may have the same problem - around half worked OK when I last fired up the Beeb 4 or 5 years ago.

electronicskip
Thanks for the useful link. I'll try the *DRIVE 1 / *CAT approach. All the lights on the drives are doing what they should and the disks spin when I type *ADFS but then I get the error message.

I shall also find out what 'Disk Rot' means - sounds ominous.

- Peter

[WaveyDipole]

I found a reference manual here:

http://chrisacorns.computinghistory....SystemUGI2.pdf

It indicates that the error means that the compurter cannot read the disc and gives several reasons:
- disk is damaged
- disk is unformatted
- disk is the wrong type (80 track in a 40 track drive)

It could also mean that the 40/80 switch (if it has one) is in the wrong position for the disk being used or that the disc is not properly centered (unlikely for multiple discs though).

It is very probable that the disks may have gone bad given their age, but its curious that you get exactly the same error on all of them. If that 00/00 means sector 00 track 00, that may imply that the drive can't even read the boot sector so maybe this points to another problem such as the wrong mode (does it have a 40/80 track switch?) or a mechanical one such as the heads being dirty and needing cleaning. Do you get this on both drives?

[AC/HL]

I have a Sony digital camera which uses floppy discs. I have quite a few, but some do seem to die for no apparent reason. Nothing visible, I just bin them, but some are quite old and there's nothing of value on them.

[SiriusHardware]

I remember that model.

I seem to remember it had an exceptional optical zoom for its time. The achilles heel was always going to be the 1.4MB limit imposed by the discs, unless you carried a box of discs around with you of course.

That used 3.5" discs didn't it?

The ones used by my Atari ST seem quite resilient. I get the ST out every few weeks or so and there aren't any discs I've recently tried that are not still working perfectly. (Probably a stupid thing to say - now they will all start dying on me).

[AC/HL]

Yes, just standard HD discs. Doesn't seem to matter which brand, but as I said I don't really take much notice.

[G3PIJpeter]

Originally Posted by WaveyDipole

... reference manual ... indicates that the error means that the compurter cannot read the disc and gives several reasons:
- disk is damaged
- disk is unformatted
- disk is the wrong type (80 track in a 40 track drive)
It could also mean that the 40/80 switch (if it has one) is in the wrong position
Do you get this on both drives?

All disks were formatted 80-track ADFS so I put the 40/80 track switch in the 80-track position. Without taking the drive apart, I am beginning to think that dirty (corroded?) heads are the source of the problem. Next step is to try some of the *DIR and shift/break etc. moves suggested here by others.
- Peter

[SteveCG]

I've had many floppy disk drives where the grease had gone hard. What you need to do is to open the drive up and carefully re-lubricate both the sleds and the worm drive that moves the head. You can also ever-so-gently clean the heads (even though they should NOT have made contact with the floppies working surfaces) using a cotton bud soaked in Iso-Propyl Alcohol (IPA). I reckon I've had a 90 odd percent success rate.

A further thought: Do you have any other computers with floppy drives? Is so you could try formatting a blank disk and if successful try formatting that disk on the Beeb system (provided you have the appropriate type of floppy, ie number of sides and density) as a problem 'confirmation' check

[Backtoreality]

Not wishing to state the obvious but are the discs formatted as dfs discs rather than adds ?

[G3PIJpeter]

I've cleaned the heads and checked that the other mechanics in the disk drives are OK. All ADFS disks still refuse to boot. However, I tried three 'Softlab' educational 80-track DFS disks - one worked absolutely fine and the other two refused.
So ... it seems to me that the drives are mechanically OK but the disks themselves (always formatted ADFS except the 'bought-in' Softlab educational ones) have been slowly corrupting over time, most likely due to stray magnetic (or AC) fields. The room where they have been stored is the 'ATU' end of my 25-metre aerial that is fed with up to 200 watts on the HF bands, although I would expect 50 Hz (or the Earth's magnetic field?) to be more potent at de-magnetising/randomising the particles in a disk surface. The refusal of disks to boot has been steadily increasing over the years to the point where now I have just one that works!
I know this is not the place to advertise, but I think it is time to put my Beeb into the offers category under 'FOC come and get it' - or take it down to the tip.
Many thanks for all your suggestions - Peter

[AC/HL]

It's a bit hazy now, are discs "soft sectored" by low level formatting during manufacture.
Assuming the coating is OK, is it possible to do a low level format?
Obviously, all data will be lost including the normal formatting, or is this rubbish?

[mhennessy]

I'm pretty sure that a blank floppy is just that - blank. When you format them on a BBC micro, that is, in effect, a low-level format.

I once accidentally put a hard-sectored disc in a BBC micro drive, and it made some highly amusing noises! No harm done, but obviously no success in reading or writing

Most of my BBC micro disks are DFS - I never did that much with ADFS at the time. I wonder if the greater data density of ADFS renders them more vulnerable to external magnetic fields? All this talk of "disc rot" has scared me a bit - I did put them up in the attic earlier this year, but I reckon they'd be better in a more controlled environment.

The trouble with floppies is there is no mechanism to report the strength of the signal coming off the heads. Fine today, gone tomorrow. Having a choice of several different disc drives from different manufacturers might help...

[cmjones01]

I've known floppies to deteriorate with time, but I've got a large collection of DFS discs for my Beeb, all dating back to the mid-1980s, and almost all of them still work, so I'd be surprised if yours had all died.

Though ADFS did use double-density (MFM) recording, as I understand it the distance between magnetic features on the disc isn't actually less than with single-density (FM) formatting, it's just a more efficient modulation method. So I'd be surprised if they were more prone to dying than DFS discs.

It's possible that the drive has wandered out of alignment, maybe due to some plastic part warping with time. Trying the discs in another drive is the obvious test for that, though it may not be so easy. I'd be happy to try some in my Beeb if you like, though it would involve posting them.

To exonerate the drive from blame, I'd try formatting a disc. The Master doesn't have an ADFS formatter built in, only a DFS one, but that should be good enough for a test. If you can bear to delete the whole contents of a disk, try

*FORM 80 0

then

*VERIFY 0

If that completes successfully, the drive is healthy but may still be out of alignment.

Chris

[G3PIJpeter]

Originally Posted by cmjones01

To exonerate the drive from blame, I'd try formatting a disc. The Master doesn't have an ADFS formatter built in, only a DFS one, but that should be good enough for a test. If you can bear to delete the whole contents of a disk, try *FORM 80 0 then *VERIFY 0 - If that completes successfully, the drive is healthy but may still be out of alignment.

I tried to format a disk as above and each time different amounts of time went by bink-bink-bink before "disk fault xx at yy" came up on the screen. Same result with *FORM 80 1 in the other drive. I now think the mechanics of the drives are at fault because my one 'good' disc (Softlab Measuring and Weighing) now fails to load (as it successfully did a few days ago - see above).

So . . . it's definitely a basket case. I shall offer it next week FOC for attention by brains better than mine or, if no takers, regretfully take it to the tip.

I give up - thanks for all your input - Peter

[Mike 123]

SteveCG, I get disc error 18 @ 00 etc. Your suggestion sounds good re cleaning the works of the disk drive. My problems is finding the parts you mention -"sleds" and "worm drive". How much 'taking apart do I need to do. I have a spare Cumana I can work with to practice on.
Are there workshop manuals for such as these. I should add that this machine was last used 20/30 years ago. Master now works OK. Need the disk drive. Help! Mike 123

[Okto1984]

Originally Posted by G3PIJpeter

I know this is not the place to advertise, but I think it is time to put my Beeb into the offers category under 'FOC come and get it' - or take it down to the tip.

Maybe you'll have some results with the disc drive, but it's not essential to have a working drive any more. You can buy storage devices using modern flash memory that attach to these computers. I use my BBC master almost entirely with a compact flash card fitted on a board inside. The disc drive is used occasionally for when I buy new software, or to share programs I've written with friends, but I could easily live without it now and just use a PC to make a suitable flash card with all the programs and games on.

[SteveCG]

Mike123,

I've dealt with the floppy drives used in PCs and early Macs. I've found that all that is neccessary is to unplug the units, extract them from the computer/housing and gently ease off the thin metal top of the unit. This should reveal the head(s) which are mounted on a sled that slides along a smooth rod (or rods on some models). By looking, you'll see a small motor with a worm drive that has a small spigot in the worm thread that is attached to the sled. All you need do is clean off the old grease and re-lubricate with fresh grease. You should not have to dismantle anything inside the drive - indeed I would say strongly - do not dismantle anything inside !

Probably the trickiest thing is easing off the metal top casing.

By the way, you can run these drives without the lid on, so you can see what is mechanically happening.

Also you might find some accumulated dust in the unit (some drives I've met have been absolutely clean - others seem to have 'the dust of ages' in them) in which case use a soft fine-art painting brush to gently get rid of the dust.

[cmjones01]

The grease thing applies to 3.5" drives, I think. Most 5.25" drives I've seen don't use the worm drive, but have a stainless steel band pushing the head to and fro. There's no grease involved, usually.

Chris