Original Tandy 1000 no boot

[falter]

I ended up buying a Tandy 1000 off ebay for a decent price (actually two, I got an original 1000 and then a 1000TL for $75 each).

The 1000 powers up and posts, but on power up the disk drive LED is perma-lit, and it makes no obvious effort to actually try and boot.

This 1000 appears to have had its original 360k drive swapped out in favour of a pair of the drives used in the Tandy 2000. I believe these are 720k if I'm not mistaken.

I did try swapping a known good 360k, changing cables, etc.. but no dice. So I'm wondering if there's much else I can do here or if we are looking at a floppy controller problem.

[Eudimorphodon]

You've checked and ensured that pin 1 is correctly aligned between the drives and the motherboard, correct?

[falter]

Yup. Checked and triple checked. Only one drive lights its LED.

And I was incorrect.. these are 360k drives.. Toshiba FDD 5401.

The drives don't even spin or anything.. just the top drive light is on at power up and boot fails.

[Eudimorphodon]

Check your 12v line, it could be dead. That would explain no spinny-motor but the rest of the electronics working, a Tandy 1000 doesn't use the 12v for much. Is the power supply fan spinning?

[falter]

Yes.. fan is working at full blast. I'm thinking this may be FDC chip failure.

[tipc]

The Tandy 2000 drives will not work in a 1000 or vanilla pc. Personally I've never heard of a 5 1/4" 720k drive, not that there were many, that was pc compatible. Maybe they fiddled with jumpers, if there are any, to try and get the Mitsubishi 4853-1s, iirc, to work.

[lowen]

The PC originally used Tandon TM100-2 drives or equivalent as I recall; Tandon's TM100-4 is the same drive in 96DPI trim and will format out to 720k. I had a few of these back in the day, but I wasn't running PCs either. I actually had a few TM101-4 drives, the ones with buffered seek, but they were difficult to get to work with my machines of choice back in the day.

I personally haven't seen one in the wild with 720k 5.25 drives, but if the PC in question is able to support 720k 3.5 drives it can support what were, back in the day, called quad density drives. They were common in the non-PC world.

The hobbyist can always repurpose some AT 1.2MB 5.25 drives as 720k QD drives, and I have seen that, but it was a hobbyist build. The 1.2MB unit just needs to be able to run 300 RPM (not all can) to make that work.

[Agent Orange]

Concerning the 1000SX, I've personally never seen or even heard of a 5.25 720 floppy drive. If it exists, possibly Japanese? My SX has a 360 and 1.44 3.5 configured as a 720. The default BIOS settings are pretty much chiseled in stone so one would have to get creative in that area. I'd like to hear more about that 5.25 720 if it does exist.

[falter]

Yeah I made a mistake in identification the drives. These Toshiba drives look very similar to the ones used in the Tandy 2000, which I understand are quad density.

I thought perhaps someone had upgraded for more capacity. However on closer inspection, these are not those drives. These have a slide lock on them the 2000 drives do not have. These are 360k Toshiba. What these are doing here I'm not sure.. probably just replacements. They were missing screws on one side so even though this is an earlyish 1000 I don't think these are drives Tandy used.

Regardless, I've now tried three different drives in the system, along with cables, and the result is always the same.. solid light on one of the drives at power up, system pauses like it is trying to read a boot disk, and then fails.

[Eudimorphodon]

Concerning the 1000SX, I've personally never seen or even heard of a 5.25 720 floppy drive. If it exists, possibly Japanese? My SX has a 360 and 1.44 3.5 configured as a 720. The default BIOS settings are pretty much chiseled in stone so one would have to get creative in that area. I'd like to hear more about that 5.25 720 if it does exist.

"Quad Density" 5.25" disk drives go back to the late 1970's and while rare did show up either as stock or as options for quite a few machines up into the MS-DOS era. (Like the aforementioned Tandy 2000.) Strictly speaking I can't think of a reason why you *couldn't* use one on a PC other than the BIOS limitations, but that isn't even that big of a deal. I'd think you should be able to treat one exactly as if it were a 720k 3.5" drive. (It'll be the same format, 80 cylinders of 9 sectors per track.) My dimly-remembered experience with sticking 720k drives in original XTs that only supported 360k drives is that even if you don't use driveparm or driver.sys DOS will get from the disk format that you're using 80 tracks and behave accordingly; you'll just need a hacked version of FORMAT or use DOS 3.2 or later with DRIVEPARM to format disks.

The gotchya is the BIOS would have no built-in facility for double-stepping the drive to read standard 40 track disks, so you'd either need to write your own driver to handle that or just settle for having to use a machine with one standard drive and one quad density to do all data transfer.

Anyway, per the issue with the Tandy 1000, I believe the original 1000 uses a standard FDC chip instead of some Tandy-specific ASIC, which is good if that is blown out.