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External 720K floppy drive IBM XT

robbo007

Experienced Member
Joined
Jan 7, 2012
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287
Location
Iberian Peninsula
Hiya all,
I've got an external IBM floppy drive hooked up to my XT. Seemed to read a disk for a second then fail on reading. Could be dirty heads. I've managed to get one side of the plastic case open but can't seem to get in any further to get to the heads to clean. I've tried a cleaning disk but really want to see the heads and check condition.

Any ideas how to get in further without breaking the plastic?

Here are the pics.
 

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The cleaning disk is sufficient. Opening the drive will only get you more trouble. I don't know what looking at the heads can tell you.
 
Try the cleaning disk first. If that fails, then disassembly is needed. Something big might be jamming the mechanism or it may be necessary to replace the drive.

The PC Family Service Manual has a diagram of the parts for the 4865 external floppy drive. Ask again if you do decide to conduct the disassembly so one of those with one can verify the correct way. I think I remember a method but I am not sure and don't want to steer you wrong.
 
Drvparm needs to be setup correctly and you need to boot from an internal drive

On my drive I could format and read disks made by the drive itself but not from other machines
 
Just to check its not a configuration error. I'm booting MDDOS 6.22 from floppy disk I made. the config.sys has the following command for the driver. For some reason Dos 3.21 does not like the driver.sys.

DEVICE=A:\DRIVER.SYS /d:2 /f:2

I've also tried with the /C for the drive door just in case.
Is this correct?
 
Right, as rmay635703 mentioned Seems to format a disk fine. And can read it but can't read disks formatted on other computers. How strange???

Are there any work arounds for this? Or is this a limitation. I'm stoked the drive works though :)
 
Right, as rmay635703 mentioned Seems to format a disk fine. And can read it but can't read disks formatted on other computers. How strange???
Are there any work arounds for this? Or is this a limitation.
Not a limitation according to the announcement letter for the 4865, which is at [here]. The letter includes, "adds the ability to interchange data between IBM Personal Computers with 5.25' diskette drives and those with 3.5' diskette drives."

Maybe the radial head alignment is out on both drives.
 
Right, as rmay635703 mentioned Seems to format a disk fine. And can read it but can't read disks formatted on other computers. How strange???
These are the classic symptoms of an alignment issue.

What about reading a disk made on the external floppy on another computer?
 
These are the classic symptoms of an alignment issue.

What about reading a disk made on the external floppy on another computer?

I don’t think that’s it, I had a stack of 5 drives all of them had the issue that they could only read disks made by another 4865 on the 5150, could never move data from another 720k system to the pc.

It may be a strange bios problem or something else causing this issue but I doubt every 4865 has the exact same alignment issue unless it’s a manufacturing defect
 
I don’t think that’s it, I had a stack of 5 drives all of them had the issue that they could only read disks made by another 4865 on the 5150, could never move data from another 720k system to the pc.
IBM clearly states that this drive has that exact capability:

Not a limitation according to the announcement letter for the 4865, which is at [here]. The letter includes, "adds the ability to interchange data between IBM Personal Computers with 5.25' diskette drives and those with 3.5' diskette drives."
 
The drives in the 4865 are the same as the 5140 so data interchange there should work. But if the drives were all slightly out of alignment when manufactured, how would anyone know? The only drives to test against would be other drives made for IBM.
 
But if the drives were all slightly out of alignment when manufactured, how would anyone know?
I am pretty sure that the manufacturer would have had processes in place to ensure that just-made drives were in alignment. At that time, being a supplier to a big company like IBM could be fatal if 'bad' equipment was supplied to them.
 
Two possibilities: (1) speed error, (2) alignment issues. Speed is easiest to tackle. Use any RPM-reading program, such as IMD. Alignment is a bit thornier, but doable.
 
Disk made on the external floppy does not read on another computer. I get sector errors.
Because of this:
I don’t think that’s it, I had a stack of 5 drives all of them had the issue that they could only read disks made by another 4865 on the 5150, could never move data from another 720k system to the pc.
You may be dealing with a bad batch of drives. Unless you're really good I don't think aligning a 3½" floppy drive is something you'll have much success with as a novice. I wouldn't even attempt to align a 3½" floppy drive and I'll bet you're probably better off just chalking it up to what it is and moving on.
 
Would be good to see what floppy drive controllers everyone is using here. To see if it's a compatibility issue. I'm just surprised that so many drives are showing the exact same problems.
 
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