View Full Version : Faulty 5 1/4" Floppy Drive

October 21st, 2017, 09:34 AM

I've been asked to retrieve some data off some 5 1/4" floppy disks for a family member. I have an old 5 1/4" drive that I kept hold of for this very reason: a Panasonic JU-475-4 AKJ. This drive has been in storage for at least ten years, but was previously known working.

Having tried the drive in two different systems, I get a long wait when i ask it to read a disk, before eventually failing (disk spins and LED lights up at appropriate times). When attempting to format a (known good) disk (through MS-DOS' format) I get the same wait, and eventually a 'drive not ready' error. The head servo appears to actuate correctly. BIOS settings all checked, etc.

I've noticed that the motor activates as soon as a disk is inserted, even before I've lowered the lever to bring the heads together. Testing the drive connected to a bench power supply, I find that when the media detect sensor is actuated (with a slip of card) the motor spins for twelve seconds. If the card is present when power is turned on to the drive, the motor doesn't spin, but does when the card is removed/replaced.

(I've consulted a service manual I found for the JU-475-4 (here (https://data2.manualslib.com/pdf4/89/8893/889295-panasonic/ju4754.pdf?32892fe71a432f629218aea395a2d8e3)) and tested pins 8, 10 and 12 leading to the media sensor. Pin 8 reads ~1.25V, pin 10 0V, and pin 12 reads 0V when media absent, 5V when present. The diagram shows this signal goes pretty much straight into the IC.)

It's been well over a decade since I was last using this drive, and I can't remember if it's always behaved this way. So before I rush off following any red herrings, can anyone tell me if my drive should be spinning up this way?

Thank you in advance.

October 21st, 2017, 10:13 AM
Run a cleaning disk with solvent through the drive to clean the heads. That's always the first step when a drive fails to read/write.

October 21st, 2017, 10:16 AM
Also check that your BIOS is set to the right drive type (360k or 1.2mb), and that your drive is jumpered and/or cabled properly.

My Epson 1.2mb 5.25 spins when a disk is put in before you close the latch, it works fine otherwise.

October 21st, 2017, 10:31 AM
My Epson 1.2mb 5.25 spins when a disk is put in before you close the latch, it works fine otherwise.

That's the way it's supposed to act--ever since about 1979, drives with DC spindle motors do this to ensure that the disk is seated correctly. Even 3.5" drives will do this.

For the OP: First of all, is your drive terminated correctly? If this drive is part of a 2-drive setup, then the answer is usually that one drive or the other is properly pulling up the signals to the drive. I believe that Panasonic drives have a termination jumper.--if so, make sure it's enabled.

Secondly, if you've got a 'scope or a logic probe, make sure that when the drive is selected with a disk spinning in it, you get a pulse on the INDEX/ pin. I've seen drives with a bad LED in the index sensor produce a steady "not ready" status.

October 21st, 2017, 10:42 AM
1.2mb drives will normally spin the drive motor briefly as the disk is inserted. After the disk is inserted the drive will continue to spin until the drive detects the first index pulse, or for a few additional seconds if it can't detect the index hole for some reason. If no index is found, a 1.2mb drive will not enter a "ready" state and you will not be able to read data from the disk.

Was this drive from an IBM PC compatible system? If not, you may need to change various compatiblity option jumpers.

Make sure the index sensor and track zero sensor are free of any dust or residue.

October 21st, 2017, 11:02 AM
I thought PC compatibles used soft sector disks. Do they have index sensors?

October 21st, 2017, 11:18 AM
Yup--why do you think every soft-sector floppy has an aperture in the jacket and a hole punched in the cookie? How else does one tell where a track begins and ends?

Soft-sector floppies have but a single hole to indicate index; hard-sector floppies have holes added to indicate the start of each sector.

If the controller doesn't see the index signal, then a deadman times out and you get the "Drive not ready". If the controller sees the index pulses, then it will give either "Sector not found' or "General failure" errors if there are other problems with the disk/drive.

October 21st, 2017, 12:05 PM
I thought PC compatibles used soft sector disks. Do they have index sensors?
AFAIK all diskettes have at least one index hole; as Chuck explained, soft sector just means there is only one index hole whereas most hard sector disks have 11 or 17. AFAIK all PCs use soft-sector diskettes; not many small systems used hard-sector diskettes, notably North Star, Vector Graphic and others using the Micropolis controller, and Heathkit IIRC.

You may be thinking of systems like Commodore which ignore the index hole(s) altogether and can use both soft- and hard-sector diskettes.


October 21st, 2017, 06:38 PM
So PCs are not really soft sector then. After all that hole isn't software.

October 21st, 2017, 07:36 PM
So PCs are not really soft sector then. After all that hole isn't software.
Soft versus hard can be interpreted as flexible versus fixed.

Format a 'soft sectored' 2S2D 5.25" floppy via DOS 1.1, and DOS will have the PC floppy controller create 8 sectors per track.
Format the same floppy via DOS 2, and DOS will have the PC floppy controller create 9 sectors per track.

Even if the 'soft' is interpreted as software, in the above example, DOS (software) is controlling the sector count (within certain limitations).

October 21st, 2017, 07:43 PM
In hard-sectored media, a sector start is indicated by a sector hole, not to be confused with an index hole.

For example, a 10-sector floppy will have 11 holes--one for each sector and one in-between two sector holes for the index marker.

It can get a little more complicated on 8" hard sector floppies, which always have 33 holes. Some drive hardware allows for dividing the sector frequency by 2, 4, or 8, to allow for longer sectors. But still, the start of a sector is indicated by a sector hole. On many 8" drives, the sector pulse is brought out on a separate pin from the index signal.

Hard sectoring allows one to dispense with a lot of preamble/postamble code, so you can, in theory pack more sectors per track (e.g. 32 rather than 26 in the case of 8" floppies).

Some ESDI drives also use hard-sectoring as do many mainframe and minicomputer hard drives.

October 22nd, 2017, 12:28 AM
Thank you all for your comments. (I'm glad to see I've kicked off a tangential conversation on hard/soft sectoring too!)

You've jogged my memory that floppy drives should spin briefly when a disk is inserted. The 12 second spin in this case is clearly excessive.

In answer to Chuck(G) and SomeGuy, I think you have the right idea. A visual check says the index sensor is clean of dust. I've wired up my cheap & cheerful oscilloscope to the INDEX pin (pin 8 on the ribbon, also Testing point 7 on the PCB) when the drive is powered by a bench power supply, and I see no pulses at all when inserting a diskette. Getting my probes to bare wire on the index sensor is a bit tricky, but I'll give it a go later on today. I presume that the LED and sensor are infrared, rather than visible light?

In response to other suggestions, this drive comes from PC-compatible heritage, and was working for me in a PC when last used 10 years ago, so the more exotic jumper settings shouldn't be a problem. BIOS settings are correct (BIOS option to check floppies on boot passes too). For lack of a cleaning diskette, I opted for the alcohol/cotton bud approach. Termination is disabled, as the drive was being used as a B drive in the middle of the ribbon. (I'm assuming the 3 1/2 A drive is correctly terminated. At the very least, it's working correctly!)

October 24th, 2017, 12:43 AM
Hello again, reporting back on further progress.

When I came back to the floppy drive last night, I probed the index hole sensor directly and found that it was responding correctly to light/dark. (Low when floppy out, high when floppy inserted, dropping low periodically when floppy inserted and spinning.

I then revisited the INDEX pin and found that it was indeed dropping low (assuming I'd closed the latch on the floppy drive), and that the motor stopped spinning shortly thereafter. I could then format a disk in the drive (360k DD) and write data to it. Having removed, attempted a read, and reinserted the disk (to clear any disk-change logic) it could still see and read the data written.

I can only theorise that there was an awkward speck of dust on the sensor that I had unknowingly shifted out of the way at some point. Now to try and read these ancient diskettes I've been handed.

Many thanks to you for your pointers and advice.