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Resurrecting a IBM 5150: 601 code at POST. Need some help.

madmaxamdam

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Oct 25, 2012
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Well, that's not the "original" 5150 floppy controller. The original one has a number of metal-can IBM hybrid circuits on it. The one you have is a later version of the controller.

Sure! That has already been clarified. This PC has been manufactured in 1984, so it has a newer revision of the controller.
It's "original" in the sense that it has been assembled by IBM at production time (as opposed to being assembled/replaced by a third party later on).

Btw, playing with the old lady I found there's still a residual issue. :(

One of the FDD (I chose to be A) is totally OK, while the other (B) works fine until the header stands on track 1 (e.g. issuing a DIR command), but it fails if the header has to seek any file. In such a case the FDD header bounces up and down a few times, and after a while an infamous "Data error reading drive B" is issued.

If you have 1'40" to waste, here's what happens: https://www.youtube.com/watch?v=OBXOZCXOVZ4

You will first see the elegant drive A: header nicely and flawlessly performing its job, and then the disgraced drive B: header miserably failing.
 

Chuck(G)

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"Data error" has a very specific meaning in floppy diagnostics. The sector containing the data has been located by the controller, but the computed CRC after reading the data field doesn't match what's recorded on the disk. Probable causes (in the order that I'd consider them):

1. Dirty heads
2. Drive speed (less critical on outside tracks, more critical on inside ones)
3. Alignment/azimuth

The good news is that the drive basically works.
 

madmaxamdam

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Oct 25, 2012
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Italy
I'd bet on #2 (drive speed), for the following reasons:

- the behaviour of the FDD is absolutely deterministic: for any given diskette it always perfectly reads outer tracks and gives the data error when accessing inner tracks. I wouldn't expect this pattern for dirty heads (which I cleaned thoroughly beforehand) or wrong azimuth;

- when the disk spins, this drive is a bit more noisy than the other one (on the YouTube video, if you listen carefully you will hear it) - this noise may be due to some kind of friction inside the unit?...

Would it make sense trying to lubricate the wheel axis from the bottom of the unit?
 

madmaxamdam

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Oct 25, 2012
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Wait a minute!

A speed difference would actually affect the outer tracks MORE than the inner ones, wouldn't it?

I mean, a given angular speed diff (rad/s) will be trasformed in a geater linear speed diff (m/s) if the radius is greater: therefore the outer tracks (i.e. greater radius) should be more difficult to read - which is countrary to what I have experienced.

*scratches head*
 

madmaxamdam

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Oct 25, 2012
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Location
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With your working drive you might want to run Imagedisk to check drive speeds and alignment.
http://www.classiccmp.org/dunfield/img54306/imd118.zip

That's definitely the tool I'm in need of! The only problem now would be to transfer it on a 5.25" floppy disk from my super-modern PC that "only" has DVD/RW drive, USB Ports, and ethernet connector. I've got an old PC with CD reader and 3.5" floppy drive. But I do not own a PC with 3.5" and 2.25" drives for the last transfer.

First thing I'll try to do is to dig into the huge 5.25" disk pack I inherited with the PC itself. If I'm very lucky I may find that tool (or an equivalent one) into one of those...
 
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