PC AT 5071 Floppy drives

Hello

I have a IBM AT 5070, first mother board, 512 memory, No HD, two floppy 1.2 MB and 360 and color monitor.

Question:

The computer was working with both floppy. All of a sudden neither floppy worked. They both stopped at the same boot time. The disk controller is for 2 HD and 2 FD. When I try to boot both lights come on in sequence; A then B back to A. Then It goes to IBM Basic from ROM.

When this happened I though maybe lost BIOS. Reconfigured with information I got from GSetup which made no difference at all.

What do you think may have happened?

Thank You

Paul

Check to make sure the floppy drive cable is correctly installed. At least, the couple of times I had a similar problem it was caused by having the cable off by 1 pin.

Test the drives on a different computer if possible. Having a cable fail or the controller fail won't be too surprising; they are about 25 years old. Someone else would have to supply you with probable suggestions on possible fixes to a controller card.

Also check that you're getting +12 and +5 at the floppy power connectors. When you insert a floppy, listen to make sure that the drive spins the disk briefly (all half-height floppy drives do this to ensure that the disk is centered over the hub). If it doesn't, it's a pretty sure sign that your +12 isn't happening.

You've got a 5170 with no hard drive, and two floppy drives. In that configuration, the 5170 will access both floppy drives during 5170 start up, bot only attempt to boot from drive A:

You can't boot from A:, and so can't boot DOS. Therefore, how did you determine that drive B: is faulty? I'm guessing that you either swapped the two drives, or tried to access drive B: from BASIC.

Chuck(G) said:

Also check that you're getting +12 and +5 at the floppy power connectors. When you insert a floppy, listen to make sure that the drive spins the disk briefly (all half-height floppy drives do this to ensure that the disk is centered over the hub). If it doesn't, it's a pretty sure sign that your +12 isn't happening.

Click to expand...

Hello Chuck
Thanks. The power supply is ok. The 1.2 floppy spins; when disk is inserted and at cold boot.
What I have just realized now is that when I insert a blank floppy and do a cold boot. The floppy spins and software does not stop and tell me the disk in not a system disk; which it use to do regularly. With this observation tells me that the cmos information is not getting to the motherboard memory or it is but memory is bad (will not hold code from the CMOS).

What do you think?

Paul

Paul, a blank floppy will not get you a message; the system should just go to BASIC after sitting around doing nothing for a while.

There's another aspect that really messes with things--1.2MB floppy drives spin at 360 RPM, while 360K (48 tpi) drives spin at 300 RPM. So, if the CMOS configuration thinks that you're using 360K (48 tpi) drives and you have a DSDD/360K floppy inserted, it will try to read it using the wrong data clock frequency. Similarly, the opposite applies.

So, the first task is to make sure that the battery is good and CMOS contents are being saved across power cycles. Then you need to make sure that the floppy drive type in the configuration actually matches what's in the box.

Make certain that the floppy media type (DSHD or DSDD) matches what you've formatted the floppy for.

Then, you need a system-formatted floppy to boot. Note that a DSDD (48 tpi) 360K floppy will boot in a 1.2MB drive, but not the other way around.

I under stand what you wrote in your last post.
Chuck, I must back track some. The configuration I have on the AT is the same now as it was when I first installed Dr-DOS on a floppy. The disks that contained the installed dr-dos ran well. I was able to access B: and md there. So when I say that the system will only get to finding both floppy's and then load DOS from ROM. The system has not changed as far as what I did to get DR-DOS loaded and running. Even my master disks for DR-DOS will not load or the diagnostic disk I had made from an older copy disk; using copy disk.

I am at a lose.

Thank You
Paul

I'm assuming that the CMOS configuration hasn't changed. That both drives stopped working at the same time and you have +12 and motor function does narrow things down a bit.

Do the drives perform a seek at all--in other words, do the heads move when the system is powered up? If not, the next two things I would check would be the drive cable (perhaps a conductor or connector has failed) or the floppy controller itself (perhaps a driver IC has failed).

Yes the head on A seeks before it stops and the computer loads dos from ROM.
Is it possible that part of my ram is bad?

abpccpba said:

and the computer loads dos from ROM.

Click to expand...

I'm sure you meant "BASIC from ROM".

Chuck(G) said:

That both drives stopped working at the same time

Click to expand...

Chuck. The OP didn't answer my question (at post #4). Therefore, at this point, I think it is not safe to accept the fact that drive B: is faulty. I suspect that the OP tried placing their boot floppy in B:, and when the 5170 didn't boot from B:, incorrectly assumed that that meant that drive B: was faulty as well.

Oh, okay--sometimes I take things too literally and assume too much.

The next thing I'd do is to swap the cable connections to both drives--nothing else need change--just take the 34-conductor edge connectors on both drives and put the one that was on the first drive on the second and vice-versa. What was your A: drive is now your B: drive and conversely...

That should tell you if the drive itself is at fault.

I took your direction about swapping drive cables and found nothing changed. I found a new used floppy cable and installed it and found that there was no change. I am going to assume that the old cable was not the problem. I have look at the drive controller and found no obvious burns bad joint etc. I then put it back into another socket and the computer and drives did the same as before; ending at Rom basic.

I have been using the same floppy as the system built back awhile. So it could be that the first sector on the disks have been corrupted or just physically broken scratch Magnet. At this point I do not have the facility to make some new ones to make new tests with.

I am at a stand still until I can find another source of loaded floppy's. I have an old computer that I will try to get a 5 1/2 drive to work in.