View Full Version : Laser XT not recognizing a Seagate ST-250R Hard Disk

May 24th, 2017, 07:03 AM
When the computer boots up, the hard drive's LED comes on, stays lit. The fairly noisy drive spins into action. After the memory check, the BIOS reports that it can't find any drives. With the DOS 5.0 boot disk in the drive, I type debug, <ENTER>. I then type g=c800:5, <ENTER>. A seagate format menu appears and asks if I would like to try Drive 0 or Drive 1. Regardless of which choice I make, it says it can't find a device. So it appears, there is no way to low level format it.

Checking the ribbons, both are plugged into the ISA controller card firmly. I have unseated and reseated the card itself. I have taken the drive out, unscrewed the controller PCB from the bottom and inspected it for any blown circuits or burn marks -- none found. Using my multimeter, I checked the voltages on the molex power cable that goes into the hard disk. One reads 5.16V, the other is 12.63V. I believe this is very close to the stated requirements of +5 and +12V without being excessive.

The jumpers at the back of the drive seem correct. They are unchanged and place the drive assignment as DS-2, and a radial configuration.There are no other disk drives save for a floppy drive in the machine.

Here is a reference to the ST251R. As I said, J1 and J2's ribbons are connected to the data controller. (Oddly enough, when I received the computer, J2 was not.) Pins 1 and 2 are shorted on J7, along with pins 13 and 14.

I'm at a loss what to do next. Any suggestions?

May 24th, 2017, 11:28 AM
I don't think it should be set to "radial", try removing that jumper.
Is your 34-wire control cable without twist, or with twist? If the former, set the HDD to DS1.
Is the terminator installed?

May 24th, 2017, 11:41 AM
What controller?

May 24th, 2017, 11:48 AM
Does the hard drive LED come on when the cable is not attached?

May 24th, 2017, 12:14 PM
Radial select is exactly what you do want--the opposite is binary select.

Ensure that no cables are "upside down"; that is, that you've identified and matched up pin 1 on all of the connectors and cables.

Finally, if you have a "flat" control cable (the 34-conductor one), you'll need to select DS1, not DS2. Make sure that you're not using a floppy cable by mistake.

May 24th, 2017, 03:22 PM
Radial select is exactly what you do want--the opposite is binary select.
Uhm, doesn't "radial" mean separate control cable for each of the drives?
That would be rather rare in PCs...

May 24th, 2017, 03:30 PM
No, same control cable, just different drive selects. Like floppies.

May 24th, 2017, 05:10 PM
No, same control cable, just different drive selects. Like floppies.

"Each radially connected drive has its own control and data cable."


May 24th, 2017, 06:09 PM
I stand corrected. Obviously, the term "radial select" means something different from floppy drives, where the other option is "binary select". In any case, for a single hard drive, it would seem to make little difference.

May 25th, 2017, 12:59 PM
Thank you all for your responses. I learned that there is a pin stripe on the data ribbon that indicates the position of pin 1. Essentially, the ribbons were connected upside down when I first got the computer! It is now able to recognize the drive.