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Floppy Disc(s) Fail (40) after replacing battery in Dallas RTC

N

Nelson Ogden

Member
Joined
Mar 12, 2020
Messages
10
Location
East Jordan, MI USA
Hi Folks,

I have a Pentium II system with a 3.5" floppy (drive A) and 5.25" floppy (drive B) connected to the onboard FDC controller. Motherboard uses a Dallas DS12B887 RTC which I just had to modify with an external battery. After I replaced the battery, I loaded default BIOS settings and went through all the settings, changing what needed to be changed.

That process went fine, but now the BIOS is giving me a "Floppy Disc(s) Fail (40)" error. The error message seems to be related to drive B, a 1.2MB 5.25" Panasonic JU-475-4. If I disconnect that drive, the system boots fine. If I set the drive in the BIOS to 360kB instead of 1.2MB, it boots fine (though the drive won't read 1.2MB disks in Windows). I'm sure this is a 1.2MB drive, but I get the error when I set the BIOS accordingly. Before the battery failed, this system (including the 5.25" drive) worked fine.

If I continue booting after bypassing the error message, the drive "kind of" works. Windows recognizes it and can tell me how much space is used/available on a disk. It can't read the disk, though.

Only thing that changed between the time it last worked and now is the Dallas RTC battery failing so I assume its a BIOS setting somewhere I'm missing. This is a PC I built from spare parts a while back and don't recall having to change any unusual BIOS settings back when I put this PC together. Any suggestions?
 
Is your 1.2M Floppy strapped for fixed Density or Dual Density? Also it needs to be strapped for
DS1 in a DS{0..3} selection or DS2 in a DS{1..4} selection, with the twisted 10 thru 16 conductors.
Make sure the TM Jumper is installed.

Larry




JU-475-4.png
 
With the settings set to 1.2mb, try booting to DOS and running ImageDisk in alignment mode. That might give you some additional clue. You should be able to manually step over tracks, and see what sectors Imagedisk reports under the head.

Possible causes might include dust or junk in the drive preventing the head from moving when the computer does a seek test, dust over the track zero sensor, or faulty cable.
 
Thanks for the replies. It is strapped for dual density and DS2 (in a DS{1..4} selection). I had previously removed the TM jumper since the drive was not at the end of the cable. Since it is drive B, I placed it before the twist. Still, I reinstalled the TM jumper and still have the same trouble.

Then I unhooked the 3.5" drive A and connected the 5.25 in question to the end of the cable after the twist (TM jumper still in place). I configured the BIOS accordingly (with drive A as 1.2MB 5.25" and drive B as none). Still have the same error.

I'll try ImageDisk next.

-Nelson
 
If you strap it for DS2 in a DS{1..4} configuration, and put it on the end of the twisted cable with the
TM Jumper Installed as a single drive, with the BIOS set for 360 will it boot from a 360K floppy?
What about setting the BIOS for a 1.2Meg and try booting from a 1.2 Meg Boot Floppy? It should
be recognized and at least turn on the Drive LED as the system boots.

Larry
 
Finally had a chance to try a few things:

1. I tried a different 5.25" drive and it worked perfectly.

2. Ran ImageDisk. The drive responded to my commands but I noticed something. By the time I got to about track 60, the head in the drive was already at the extent of its travel. When I went back to track zero, the head went to the other end of its travel (about where I'd expect it to land for track zero). Tried this test several times and had the same result. It seemed like the drive was moving the heads too far every time I advanced one track (in single step mode, too).

3. I set the BIOS for 360kB and found a diskette I had formatted on an actual 360kB drive. It didn't boot (not sure why; it should have been a boot disk) but once Windows loaded, I was able to read the disk properly.

4. I tried a different cable. Same trouble.

Based on these tests, it seems like my drive is having an identity crisis and just thinks its a 360kB drive! Before the Dallas battery failed, I read and wrote a number of 1.2MB disks with this drive on a semi-regular basis without any trouble. Nothing changed between the time the drive worked and now except for the Dallas module.

I have the following jumpers in place:
DA, DC, GX, TM, PH, and DS2.

There are no obvious problems on the circuit board like physical damage, corrosion, etc. I'm not too concerned about this drive since I do have a replacement and this computer is something I just built for the fun of it! Not a big deal if I can't get this drive working. Just don't want to condemn it too quickly!
 
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