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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 24th May 2021, 4:09 pm   #1
MeerKat
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Default TEC FB-504 5.25” FDD, Disc centralising

Hi All,

I have just repaired two of these drives out of a Cumana dual unit for the BBC computer.

The problem was leaking capacitors on the main board that had corroded the tracks, one drive would read and the other would not read or write.

I have replaced the capacitors and cleaned the board, several links had to put on the boards to fix open circuit tracks, a lot of the tracks are only 0.010” wide.

Both drives read and write now but I have noticed with both drives that when you insert a disc the spindle motor does not run to centralise the disc. These drives have a lever you turn down through 90 degrees to clamp the disc in place. See picture.

Can anybody tell me if this is normal for this type of drive?

Regards,
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Old 24th May 2021, 4:46 pm   #2
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

Normal, the disk is cantered by its hole, no amount of spinning will make it any better. The head positioning is open loop.
 
Old 24th May 2021, 4:56 pm   #3
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

Thanks Merlin, I could have sworn it span but I must be thinking of other drives. That will save me trying to find a non-existent fault!
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Old 24th May 2021, 5:30 pm   #4
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

That’s a brand I’ve not seen for a long time, takes me back to school days.
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Old 24th May 2021, 8:14 pm   #5
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

They were used in TRS-80 computers as well.

They look well made, die-cast alloy chassis, Elna caps on the motor board, pity about those on the main board, 2 of the 4 in each drive had leaked, different ones fortunately so it was easier to trace out the open circuit tracks on these double sided boards. Some of the components are tiny so the next step would be surface mount. I’m glad to have saved them.

One of the failed caps attached.

Regards,
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Old 24th May 2021, 9:29 pm   #6
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

Quote:
Originally Posted by MeerKat View Post
These drives have a lever you turn down through 90 degrees to clamp the disc in place. See picture.

Can anybody tell me if this is normal for this type of drive?

Regards,
As far as I recall, this lever is common to most (if not all) 5¼" drives that I've used.
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Old 25th May 2021, 12:24 am   #7
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

Quote:
Originally Posted by MeerKat View Post
Thanks Merlin, I could have sworn it span but I must be thinking of other drives. That will save me trying to find a non-existent fault!
Older Teac FD-50 drives like those used by Sord would spin momentarily when the lever was closed. I can't recall newer (i.e. half-height) drives doing this, certainly HD drives didn't.

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As far as I recall, this lever is common to most (if not all) 5¼" drives that I've used.
The Teac FD-50 had a clamp arrangement. Apple Disk IIs had a flap-type thing. Apple UniDisk and DuoDisk units had a similar clamp to the old Teacs.
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Old 25th May 2021, 12:30 am   #8
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

These mid 80s Mitsubishi 5.25” drives, the black ones at the bottom, are a different arrangement to the TEC turn lever drives.

LOADING. You insert the floppy, the last inch is against light spring pressure, the floppy clicks lightly as it bottoms in the slot and you can hear the spindle motor start, then push the top lever down, this clamps the disc, locks the floppy in and the motor stops. You are ready to go. I have always presumed, perhaps wrongly, the motor running during the clamping phase helps with alignment of the disc hole.

UNLOADING. Push in the lever below the floppy slot, the top lever jumps back up and the floppy emerges about an inch ready for you to slide it out.

This is where my thoughts of the spindle motor starting when you insert a disc came from.

You can see in the picture the top drive is empty and you can just see a floppy in the lower one.

Regards,
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Last edited by MeerKat; 25th May 2021 at 12:35 am. Reason: Post has crossed with arjoll's
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Old 25th May 2021, 9:40 am   #9
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

Now that Arjoll has drawn my attention to Apple using a flap rather than a lever, I can confirm that the drives on my Apple ][ are an exception, whereas most of my 5¼" drives use a lever.
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Old 25th May 2021, 9:50 am   #10
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

I've got various BBC Micro floppy drives here. Some of them run the motor when the disc is inserted, some don't. My original Shugart SA-455 drives do run the motor for a moment when the disc is put in, long enough to centre it when you turn the lock lever. Other, more recent, drives (can't remember the manufacturer) don't do it.

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Old 25th May 2021, 10:12 am   #11
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

I seem to remember with the flap-type, which originated on full-height drives, that if the disk wasn't fully pressed in then you could end-up bringing the clamp down quite a bit off-centre and so crushing the disk.
Some of these also had an extra slide-lock button

I did rather prefer the lever-type, used by Teac etc. on most half-height drives, especially over the less-common smaller-flap ones.
And I recall that some lever-types would eject the disk a bit when lever was released, so had to be be a bit careful to push it back in fully, if turning the lever again.

I seem to recall a 4th type, with a button that you pressed to lower the clamp, and pressed again to release it and eject the disk a bit.
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Old 25th May 2021, 4:11 pm   #12
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

One of the common makes of push-button lock/eject drives was Epson. You put the disk in and pressed the button to lower the hub cone and lock it in. The press the button again to release it and the disk would then be ejected by a spring thingy so you could grab it.

The half-height one was as far as I know conventional inside. But there was also a 1/3d height one, turns up in the QX10 and the TF20 disk unit for the laptops, that had a voice coil head positioner. It was almost like a miniature RK05 head mechanism for those who remember that far back. Very odd...

There was also a drive, I think BASF, where the entire front panel was a door with a press to lock, press to release catch. You opened the door, slid the disk in, then closed it and it latched, lowering the hub cone. Something tells me the drive was an odd overall size, perhaps 2/3rds height. I've come across them in the RML 380Z.

My experience is that the very early drives didn't spin the motor when you inserted a disk, later ones often did. It was claimed to help to centre the disk, I have no idea if it actually did.
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Old 25th May 2021, 10:48 pm   #13
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

The disc drive I used with my Beeb was a 40 track, single sided unit. Half height, with a clamp that had to be pulled down to lock the disc in, and pulled down again to release the disc and flick it out enough to grab hold of. It might well have been an earlier version of the Epson mechanism Tony described, just with the clamp actuated directly as opposed to via a plunger and bell-crank arrangement.

I can't remember for sure if or not it did a brief self-centring spin when closed. It might have, but it's just as likely I am remembering a 5.25 drive from one of many other systems I have used since. They definitely did not all do it.
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Old 26th May 2021, 1:09 pm   #14
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

Quote:
Originally Posted by TonyDuell View Post
>>
>>
There was also a drive, I think BASF, where the entire front panel was a door with a press to lock, press to release catch. You opened the door, slid the disk in, then closed it and it latched, lowering the hub cone. Something tells me the drive was an odd overall size, perhaps 2/3rds height. I've come across them in the RML 380Z.
.
Yes I remember seeing those complete front cover-flap ones of those as well. I think it was on an all in one system, maybe like TRS80 (Although not one I currently have, that has full-height drives).
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Old 26th May 2021, 5:10 pm   #15
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Default Re: TEC FB-504 5.25” FDD, Disc centralising

The H17 drive cabinet for the H8 has a drive with a full front panel that drops the cone when you close the cover. I think mine is the early WANGCO model 82 that became the Siemens FDD100-5.

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