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Tandy 1000sx versus Low Leveling MF hard drive.. the lesson learned.

Patrick.B (TTR)

Experienced Member
May 11, 2011
Houston, Texas, USA
The lesson I learned yesterday
The situation I find myself in is simple, I need to low-level format two MFM drives, and the solution seemed simple enough, grab the Tandy 1000sx and "get er done". Well what seemed like a possible two hours event, turned into a "WTH" eight hours event.
I will start with: We all know IRQs are the boon of the XT and AT machines, always a fight to "does it work together or conflict, should I turn it off or on " situation.
So since I do not have a working RGB Monitor on hand, I slapped a 512K VGA video card in the computer, and LCD Monitor, and grabbed my trusted WD1002A-WX1 MFM Controller I have used so many times before of course I had pulled the "Jumper and Notes", and the Western Digital manuals and verified all jumpers are correctly set on main board and Controller, plug it to a Tandon TM502 on to it, connect my gotek to the 1000SX and start her up.,
[A few moments later]
"1701" on boot up.... and the floppy with a known working image of MSDOS 5 refuses to even "read boot tracks at all"
I spend the next hours trying to understand why this is not going on smoothly and find, if using an external video card the WD Controller needs to be the first card on the slots (nearest the PSU) to avoid conflicts, so from my findings, I swapped cards around, video on farthest and controller on nearest, power up... and...
[A few moments later]
The A> prompt shows up and I start up Ontrack Disk Manager and work the configuration but the hard drive refuses to initialize properly making me consider this drive may just be gone for good.
[A few moments later]
I continue to try different hard drives, and I keep getting the same dead-end situation. I even use a known working drive to test I am not crazy at this point, the result remains the same, and I am pretty sure something else is afoot.
[A few moments later]
After a beer and walking around the block in frustration I watch an episode of BSG75 Season 3.... then return to the problem that is nagging at me.....
[A few moments later]
I sit facing the machine then a word from a TV game show springs to mind. " Simplify " .. the 1000sx comes with Composite out from the main board already configured just pop J2S1 set to off and plug a monitor into it... So I removed the Vga card and monitor and do just that, leaving the system with just a single ISA card in it the MFM controller, and flick the switch on.
[A few moments later]
The system boots normally and the floppy boots up to MSDOS and then after a few more moments... Initializing hard drive..... and partitions are created as desired.....
I confirm my diagnostics by low levelling 3 more drives after the TM502, None failed. What a way to spend a Saturday afternoon...


Veteran Member
May 9, 2011
Upper Triassic
Sounds like you hit a perfect storm of hardware edge cases.
  • Tandy 1000s assign IRQ5 to their onboard video, so 1000-compatible MFM controllers say to use IRQ2
  • EGA and *some* early VGA cards expect to use IRQ2 for snow prevention. That’s going to clash with a Tandy 1000 jumpered MFM controller.
The OAK OTI-077 I use in my 1000HX doesn’t have an IRQ enabled so it gets along fine with a mouse on IRQ2, I assume it would also have been fine in your situation.

…. Although, dumb question: if you have Tandy video disabled is it safe to use the standard XT IRQ5 for the HDD controller?