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Tandy 1000EX Floppy Controller Issue

D10D3

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Mar 14, 2019
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Hey guys, long time listener, first time caller.
I've been working on a Tandy 1000EX and I've run into some trouble with the floppy drive. When I first got my Tandy the drive seemed to work just fine and it had no trouble booting from disks, but after a week or so the drive stopped recognizing any disk. When I attempt to access the drive it will spin the disk, but the read head doesn't seek, and after a few moments it reports a failure to read the disk.

Here is what I've tried so far:
I tried a number of different disks.
I dismantled the drive and cleaned the heads.
I built adapter cables to allow me to use non-Tandy drives and tried several, both 5.25" 320k drives and 3.5" drives with 720k disks. These all acted in the same manner as the first.
I installed a riser card in the expansion bay with an XTCF board to allow me to boot the machine without the drive and confirmed that it seems to function in all other ways.

Theories:
As much as I don't want it to be the case, I'm starting to think there could be a problem with the FD Controller on the motherboard. I dismantled the whole machine and cleaned the motherboard and I don't see any bulging capacitors or other obvious problems, but that doesn't mean there aren't any. I'm not sure where to go from here or how to diagnose it further and would appreciate any advice.
 

Stone

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Nov 3, 2009
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South Jersey, USA
Try running a diagnostic on the floppy system.

CheckIt might do it. So might Dr. Hardware Sysinfo.

It sounds like you might be right about the floppy controller. Can you disable it and put a card in with a floppy controller?
 

Eudimorphodon

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May 9, 2011
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Upper Triassic
Looking at the 1000 EX technical manual I suppose the one bright side is *if* it's the FDC it looks like it's a generic uPD765a and not integrated into one on the Tandy custom chips. So there'd at least be some hope for replacing it, if necessary?
 

Chuck(G)

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Jan 11, 2007
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Try some of the IMD testing. You should at least be able to move the heads.

I suspect it's not the FDC, but rather the buffer (usually a 7438) between the FDC and the drive, if it's an IC at all.
 

D10D3

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Mar 14, 2019
Messages
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CheckIt might do it. So might Dr. Hardware Sysinfo.
Good idea. I think I have CheckIt on my CF card so I'll try that when I get home today.

It sounds like you might be right about the floppy controller. Can you disable it and put a card in with a floppy controller?
I'll have to see if I can find a small one to find in that little bay. I'll have to ditch either my XTCF card or my ram expander though. I love the Tandy 1000 EX but it's pretty short on expansion slots.
 

Ratix

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Apr 25, 2017
Messages
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Location
Romeoville
Looking at the 1000 EX technical manual I suppose the one bright side is *if* it's the FDC it looks like it's a generic uPD765a and not integrated into one on the Tandy custom chips. So there'd at least be some hope for replacing it, if necessary?

I have this same issue with my sx model. the only difference is that i can't write to any disk without corrupting it. i gave up on the system after i replaced the actual socketed FDC chip along with the data seperator. both of these chips were replaced and still had issues
 
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