Question : Problem: SEEK ERROR READING DRIVE A:

I'm trying to repair an old 386 to computerize my electric train.  I've a great problem with the A: drive(1.44Mo).  It's impossible to boot with this drive, nothing happens... And when trying to access a disk through it, Dos "says" SEEK ERROR READING DRIVE A:  What's the problem?  The controller, the drive(other drives have the same reactions)?  Not expert in repairing computers(in fact, my sister replaces the motherboard by another one -not her, but a friend -, and now she gives me the computer back without the new motherboard, but with the old motherboard, but all cables are disconnected.  Perhaps one of the connections is wrong? ) Please help me.

Answer : Problem: SEEK ERROR READING DRIVE A:

SEEK ERROR normally refers to a problem with the drive itself.  The quickest way to determine if there is a problem with the controller is at boot up, before the system begins to boot the controller will check for the presence of the floppy drive.  The light will come on and you will hear the heads do a full sweep (sort of a vree-vree sound.)  If you get this, the odds are your controller card is okay.  The controller on the drive itself may be bad, but your description leads me to believe it isn't a problem with the floppy's onboard controller.

Here are the big things to check:
1) Is the drive firmly connected to the controller card?
      -> just press the cables in tight.
2) Do you have the cable connected the right way?
      -> on the controller cable one of the wires will have some distinguishing markings on it (normally red stripes).  This indicates pin number 1.  Look on the connector on your drive, if the red cable isn't connecting to pin 1 as labled there, it won't work.
3) Is the CMOS configured correctly?
      -> Look in the CMOS (Press either DEL or ESC normally while the memory check is going on).  Ensure that the boot sequence is set to A,C and that drive A is configured to be the correct type of drive (I guess in this case 1.44M Floppy.)
4)  Ensure you actually have a 1.44Meg floppy drive, a lot of 386's came with a 720k floppy, if you have it configured incorrectly it won't work.
5)  If you have more than one floppy drive (eg a second 1.44M floppy or a 1.2M floppy -- 5 1/4") connect the other drive as A and try booting from it.

If I was working on it, this is the order I would check things.  These days I'm a programmer, but when I was doing hardware support I saw this sort of thing a lot.  If you get to #5 and still can't get the system to boot from A, I would be inclined to say you have to replace the floppy drive.  Normally if there is a problem with the controller you will get a boot message something like
      FDD: Controller Error.

If none of this helps, let me know, I'll see if I can remember anything else.  Good luck.