Floppy drive never stops spinning

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
Post Reply
William555
Posts: 7
Joined: Sat Mar 17, 2018 2:16 pm
Contact:

Floppy drive never stops spinning

Post by William555 » Sat Mar 17, 2018 2:49 pm

Hi, I've been trying to restore a BBC Master 128, I've had to replace the batteries and so reset the cmos. And now, I can't seem to find any way to stop the drive spinning. As soon as a disc is inserted it begins spinning, and can be accessed fine, but never stops until the disc is removed. So I have to keep popping the disc in and out before and after every access.
Is there a setting I can change so it stops spinning a few seconds after access?

cmorley
Posts: 675
Joined: Sat Jul 30, 2016 7:11 pm
Location: Oxford
Contact:

Re: Floppy drive never stops spinning

Post by cmorley » Sat Mar 17, 2018 2:54 pm

Someone more knowledgable than me might know different but I think that is usually a result of the jumpers set inside the drive. If it has been set to spin up when disks are in then you don't have to wait for the motor to accelerate when you access the disk. My TEAC drives spin up when you put a disk in but they do stop again shortly after you push the lever down...

User avatar
MartinB
Posts: 4982
Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity
Contact:

Re: Floppy drive never stops spinning

Post by MartinB » Sat Mar 17, 2018 3:06 pm

Can you see if you can find a model number for the drive (a label on the drive chassis such as Teac-FD55 or similar) so we can have a look at possible jumper settings as Chris suggested. Then, if incorrect jumpers are a possibility, you'll need to remove the drive case/cover to access any such settings.

William555
Posts: 7
Joined: Sat Mar 17, 2018 2:16 pm
Contact:

Re: Floppy drive never stops spinning

Post by William555 » Sat Mar 17, 2018 3:24 pm

Thanks for the quick response guys, yes.. that would have been helpful wouldn't it!
It says TECHNOMATIC on the front I can't see an obvious model no. Maybe P/N U240B041-04 written on the pcb. It has a 40/80 track switch on the front
Jumper labels are:
TD on
DS2 off
DS1 off
DS0 on
MX off
DS3 off
It is drive 0 of a pair that were in the enclosure, but drive 1 has been removed as it was faulty.

cmorley
Posts: 675
Joined: Sat Jul 30, 2016 7:11 pm
Location: Oxford
Contact:

Re: Floppy drive never stops spinning

Post by cmorley » Sat Mar 17, 2018 3:45 pm

DS0-3 will be the drive select.
DS0 on = drive 0

MX will be single/multi drive.
MX on for single, MX off for multi

TD=?

William555
Posts: 7
Joined: Sat Mar 17, 2018 2:16 pm
Contact:

Re: Floppy drive never stops spinning

Post by William555 » Sat Mar 17, 2018 4:16 pm

Yep, I wasn't sure on mx or td...
So, from you comment I wondered if the MX would have any effect (as I'd taken the other drive out)
Sadly changing MX nor TD made any difference.
I checked its sibling, that had exactly the same jumpers except ds1 instead of 0.
So I tried that set as ds0 and connected on its own to see what it did, however that (originally labled 1, the bottom of the pair) starts the motor as soon as power is connected, even without the ribbon cable. I think that's why I took it out. (I started this restoration some months back, a popped power supply was the first issue I had about 10 seconds after the first power on. Maybe it damaged the drive somehow)

cmorley
Posts: 675
Joined: Sat Jul 30, 2016 7:11 pm
Location: Oxford
Contact:

Re: Floppy drive never stops spinning

Post by cmorley » Sat Mar 17, 2018 4:53 pm

Does the other drive have a set of termination resistors? Looks a bit like a dip chip usually. These pull up all the control signals.

You only want the termination fitted on one drive if you have multiple - so maybe it is on the drive you took out. Compare the boards and look for an empty vs full socket.

One line which is terminated with a pull-up on TEAC FD55s is the motor on line...

William555
Posts: 7
Joined: Sat Mar 17, 2018 2:16 pm
Contact:

Re: Floppy drive never stops spinning

Post by William555 » Sat Mar 17, 2018 6:29 pm

Interesting. There is what appears to be a removable terminator block (9 pins long) next to the jumpers by the edge connector.
Although, this, and all the other jumper setting I can see around the board appear to be identical.
I swapped (what I'm assuming) is the terminator form the other drive, and tried without just for fun... It seemed to make no difference. I'll see if I can get a meter on the drive enable line later to see if it gives a clue. Perhaps a cable issue, though I've tried two different ones. Thanks for the pointers so far

User avatar
1024MAK
Posts: 8022
Joined: Mon Apr 18, 2011 4:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: Floppy drive never stops spinning

Post by 1024MAK » Sat Mar 17, 2018 6:51 pm

Don't get confused between the DS (Drive/Device Select) lines and the MO or MOT (Motor On) control lines.
The DS lines are outputs from the computer to tell each drive if the computer wants to select it.
In Shugart drive interface systems (like the Beebs disk drive system), there can be upto four DS lines (the Beeb only uses two). And a separate group MO control line. Different disk drive manufacturers designed the exact motor control system slightly differently, but basically the most common arrangements are:
  • Drive motor controlled by MO signal only, so as soon as the computer activates the MO signal, all drives spin up.
  • Drive motor controlled by both MO and DS, drive motor only spins up when that drive is selected and MO signal active.
  • Drive motor controlled by only DS, drive motor only spins up when that drive is selected.
On most 5.25" drives, there are selection links to configure the drive.
Note that most (but not all) drives will only spin up if there is a disk in the drive.

BBC Micro disk systems normally spin up all drives at the same time under the control of the MO signal.

One common user fault is if the drives ribbon cable connector is inserted the wrong way round, then the drive will often spin up as soon as power is applied.

See also this web page

Mark

William555
Posts: 7
Joined: Sat Mar 17, 2018 2:16 pm
Contact:

Re: Floppy drive never stops spinning

Post by William555 » Sun Mar 18, 2018 9:24 am

Found a sticker! The drive is a Mitsubishi MF504B
So, scoping the MO and DS, both drive low when the Beeb wants to access the drive and high when it's done.
MO high is mean 4.95v, low 0.36v. DS 5.42v/0.64

So, to recap, I insert a disk, and the drive starts spinning imitiatly, and continues after the latch is closed (this is when I'd expect it to stop, is there a switch on the latch? I can't see one). From there, accessing the disk works fine except that it does not to stop spinning when the Beeb tells it.

I've unscrewed the disc present switch so I can manually press it, doing that in sync with the MO control signal kinda makes everything work as it should. So, a possible solution/bodge, put a transistor switch off the MO to control that switch and hence the motor. (Is that a dumb idea?) The down side, the disk would then not be spinning when closing the latch, is there a mechanical need for this?)

I'll probably not have time to get back to this till later in the week.
(Edit: I got high/low inverted, have corrected above)

cmorley
Posts: 675
Joined: Sat Jul 30, 2016 7:11 pm
Location: Oxford
Contact:

Re: Floppy drive never stops spinning

Post by cmorley » Sun Mar 18, 2018 9:34 am

OK.
So in that case TD is the termination resistor enable for the DSn.

I found a spec for the drive.
Mitsubishi 50xB diskette specifications.pdf
(122.27 KiB) Downloaded 18 times
There should be other jumpers or links... MM & MS which control the motor spin. Looks like you need MM connected and MS open. Page 4. There is a diagram of the locations of the jumpers/links on the last page.

William555
Posts: 7
Joined: Sat Mar 17, 2018 2:16 pm
Contact:

Re: Floppy drive never stops spinning

Post by William555 » Sun Mar 18, 2018 10:41 pm

Thanks. Ok, had a quick look this eve. The jumpers are indeed MM on, MS off. And IU on.
Although, as you suggest, this seems correct, I tried all other combos, and aside from both MM and MS on, which seemed to stop the disk reading, it didn't seem to make any difference. I've restored to the original MM on now.
However, some progress, I was messing with the other drive (which spun as soon as power was applied) and noticed it had 1v off the disc present switch (when the drive was empty). After some fiddling, suddenly the motor stopped, and the switch when pressed now goes ~0v to 5v. Even better, connecting it jumpered as ds0 (my current cable has only 1 connector) it works, and reads, exactly as my first drive.
So, plus is, I've got two working drives, but, both behave exactly the same in that they will not ever stop spinning while a disc is inserted.
I have noticed, taking a closer look at the main pcb, that although in surprising good condition for their age, both have a single capacitor that has a little corrosion at its base. Weirdly, the same cap on both drives. So I've ordered a couple of replacements to swap in just in case.

William555
Posts: 7
Joined: Sat Mar 17, 2018 2:16 pm
Contact:

Re: Floppy drive never stops spinning

Post by William555 » Thu Mar 22, 2018 10:25 pm

It's the caps! All working perfectly now.
New caps arrived, I popped off the old one that looked like it may have leaked, and indeed it had, and eaten the tracks with it. I am amazed the drives worked at all. Patching the tracks and replacing the cap on the first drive, it now works perfectly. Spinning when the disk is inserted, then stopping as soon as its clamped in, then only spinning during access.

On the second drive I found it had also eaten into the 5v in connector just behind, causing a fracture, and that was what caused the complete failure where the drive only spun on power on, and nothing else, but then suddenly starting working as I reported above, but failed again when the power cable was moved. Patched that up and replaced the cap and it too is fully functional.

I find it surprising that the same cap on both drives caused such an obscure failure, and that if it is common, that no one else has recorded the issue.
Attached is a photo of the cap (removed), there is a pair just behind the power connector, on on the 5v and one on the 12v line. It's the one on the 12v line that leaked. Hopefully this may aid anyone else that happens to come across the issue.

Big thanks for all for the help, allowing me to eliminate the obvious before resorting to the soldering iron.
Attachments
20180322.jpg

Post Reply