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Corcomp 9900 disk controller problems

Mad Hatter

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On 4/27/2023 at 6:44 PM, justacruzr2 said:

Here's a question I'm hoping someone can answer.  I am going to be testing those Fujitsu M2251A floppy drives this weekend on my PC.  The connector I need just arrived today that will convert the PC clone twisted floppy cable to the TI standard flat ribbon cable.  Should they fail, I might be able to get 2 TEAC FD55FV drives.  These are 720K drives with 96TPI.  If I understand floppy drives correctly, the capacity and TPI are governed by the controller card.  So if the CC9900 controller card can only do DSDD 360K then the TEAC drive should still work and would only format them for 360K.  I just wouldn't be using it to it's full capacity.  Also the TEAC drive writes its tracks at half the width of the Fujitsu's.  So, if what I read somewhere on the web is correct, that shouldn't be a problem either.  The heads on the TEAC should still be able to read the wider tracks of the floppies that were originally created with the Fujitsu drives.  It just doesn't work in reverse.  The Fujitsu would not be able to read the smaller width tracks.  Is this correct?  I just don't want to buy 2 drives that aren't going to work with the CC9900 Controller card.

See here for the Teac FD55 line to make the 80 track versions act as 360K:  https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/modding-a-teac-fd-55-for-double-step-(80-to-40-track-conversion)/


There's a link to a German site in the post here that explains how to get them to do 40 track stepping properly, as a 360K drive would do it.

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On 4/27/2023 at 6:21 PM, Ksarul said:

Will the FD55F drives work? Yes, with a really big caveat: the drive controller does not know to double-step the heads, so it only sees the first 40 tracks on each side of the disk. Why is this datum important? the disk will work fine in any 80-track drive with your CorComp, but it will not even be readable in a 40-track drive, as that drive will only see 20 formatted tracks per side. It "may" be possible to set the drive to automatically double-step, but you would have to read the technical manual for the FD55F drive to see if that is a possibility. On a side note, when used in a Geneve9640, your CorComp controller will actually be able to format and use 80-track drives, so you could get the full 720K formatted capacity the drives are capable of.


It would also have issues reading the normal 40-track disks, for the same stepping issue identified above. The controller does not know it needs to double-step, as the firmware in the CorComp expects a 40-track drive.

That's good news.  And I was right that once I start copying the old disks from the Fujitsu to the Teac, the Fujitsu will no longer be able to read them.  I will still save those old disks from the Fujitsu assuming I am able to get them going again.  And would you please look at the following post.  You seem to have more knowledge about these things.  And Thanks.

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Using that cable to bridge from the PC's twisted floppy cable to the straight TI cable didn't work.  So I don't know whether the floppy drives are the problem or not.  I have tried both drives with both the first release CC9900 controller and the REV A controller.  The results were the same with both.  I did connect a different drive awhile back that I bought off eBay and it did work.  But now that drive doesn't work either.  Anyway, that's why I think the problem is with the drives.  But it did make me wonder if there's something wrong with the cards that's killing the drives although I don't know how that could happen.  Maybe it's just a coincidence.


Let's assume for this discussion that the drives are OK and it's the controllers.  When I turn on the PEB, the drive spins up and the LED comes on until I turn the console on.  That's normal.  When I turn the console on, the CC9900 screen is displayed, and the drives shut down after a  moment.  That's normal.  When I press 1 for Disk Manager, the drive comes on and attempts to load it but beeps after it checks drive 1 and 2 and can't find it.  That's normal.  When I press 2 for TI Basic it goes right into TI Basic.  That's normal.  When I press 3 for TI Extended Basic the drive comes on and attempts to find and run a program on disk named LOAD but can't find one so the drive shuts down and returns to the TI Extended Basic ">" prompt.  That's normal.  When I press space bar for color bar I get the color bar.  And if I press the space bar again I get the regular TI menu with "Press 1 for TI Basic" and "Press 2 for TI Extended Basic".  That's normal.  This is just how I remember it when everything worked.


So with all that appearing normal, could there still be something wrong with those cards?  Both of these cards were rebuilt.  I replaced everything including the IC's with the exception of the PALs since they're not available.  Would the cards still appear to work even if the PALs were bad?  I know the CC9900 screen is running out of the ROMs.  It was my assumption that if the cards work normally, then the PALs are probably OK.  But maybe not?  And it appears that the PALs are different (the equations in them, not the ICs' themselves) between the first release card and the REV A card.  I tried swapping them once and the cards didn't even come on.


And one more thing.  I also checked both ends of the boot between the console and the PEB.  They just contained a couple of 74LS244's and 245's and some resistors.  Nothing looked unusual.  I was thinking that maybe there was something wrong with communication between the console and the PEB.  Not knowing what that spike traveled thru and what acted like a fuse makes me suspect everything.

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