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BBC Watford Disk drive repair wanted

PostPosted: Fri Mar 12, 2010 8:35 pm
by matsondawson
I've just bought a BBC Model B with a dual watford disk drive, but the drive won't load or format anything in either slot. It says Sector at 00/00 not found or similar. Does anyone know of someone that could repair these?

Re: BBC Watford Disk drive repair wanted

PostPosted: Sat Mar 13, 2010 10:55 am
by tezza
I don't but here are some tips. You may well know or have tried these already but just in case you haven't here they are...

Firstly, check all cables for breaks, frayed wires etc. Make sure no pins have broken off. Are the jumpers on the drive set correctly for the number of drives on the machine? This might be important depending on the type of drive. It would pay look for a manual off the web if you don't have one.

Next make sure the disk is ok. If you can find (or have) another machine with a known good disk drive, try the disk in that.

If the disk is ok, clean the disk heads. They can get gummed up especially if degraded disks are used. One of those cleaning disks are good. Be careful though, if the drive is only single sided. You need to use a cleaning disk for single sided disks or at least put tape over the non-head side. You can also clean the heads with a cotton bud and isporopyl alcohol. Just make sure you don't knock them out of alignment.

If that doesn't work, try lubricating the rails that make the heads move up and down. A touch of very light oil or silicon grease is good for this. Move the head assembly back and forwards until it seems to move relatively freely without sticking.

I've had many a drive come back to life after the above.

However, If none of the above work, it's more serious. It's either the rotation speed is off, the heads need aligning or the electronics are shot. None are easy to fix without equipment.

Watch the disk drive flywheel rotate . Is it roating freely at a constant speed? If not does the belt look ok, or is it frayed and loose? Do you have any diagnostic software which checks a drive's speed? (only useful if you have another drive of course).

Novel ways can be found to align a drive without a specific alignment disk. Check my Jan 18th, 2009 Blog posting on the site.

Logi ICS can be checked with a logic probe.

Hope this helps.

Terry (Tez)

Re: BBC Watford Disk drive repair wanted

PostPosted: Sat Mar 13, 2010 7:43 pm
by matsondawson

I've used a cleaning disc to no effect, so I opened both of them and they heads were black with crud.
I removed the crud with some isopropyl and a cotton swab, but was still having issues with the it failing to read either inner or outer tracks.
It turns out that if I give the height guide (thing that rests on the disk outer cover that the head carrier rests on) a slight bend then it fixes this, but it takes ages to work out.
That and I tried aligning the head forward/backward/angled.
So now the drives seem to work. Verfiying disks seem to come up with a few errors whatever I put it (new or old), but I'm happy enough.
I'm amazed that the disks I used are 25+ years old and seem to still work, considering they have been outside on trailers waiting for a trip to the dump.

BTW that is an excellent blog post, I may reopen it and have another fiddle when a digital oscilloscope I have on the way arrives.

Re: BBC Watford Disk drive repair wanted

PostPosted: Sat Mar 13, 2010 10:47 pm
by tezza
Beware those old disks. Any disks that have been kept for years in a humid environment will have a nice flaky surface guaranteed to gum up heads with a single spin. This is bad news for any good disks that follow as the dirty heads will gouge phonograph tracks on them.

I speak from Bitter experience.

Terry (Tez)

Re: BBC Watford Disk drive repair wanted

PostPosted: Sun Mar 14, 2010 6:25 pm
by matsondawson
Holy moly, I did notice initially disks that I put in had scratches on them.
I spent ages trying to work it out after I cleaned it, but it didn't seem to happen anymore.
Thanks for the info.