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5.25in Floppies Refuse to Format With 3.5in FloppyDrive Present

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First post, by Dolard

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I have my setup configured as follows:

A: 5.25in 360kb DS/DD Matsushita JU-455 Floppy Drive
B: 3.5in 1.44mb DS/HD Mitsumi D353M3D Floppy Drive

I'm running Windows 98 SE Quick Install on a Award PnP Flash BIOS v1.4 Boser HS-4500.

Yes I have a twist cable. Yes both drives are on DS2 (or 1 in the case of the 3in since it starts on DS0). Yes the termination resistor is on the proper drive. No floppy swap isn't enabled in BIOS. The drives are correctly assigned in BIOS and they have been verified to be the types of drives I have asserted. I have the proper disks for certain. Each drive works perfectly alone with the disks for read, write, and format (both quick and full). But the moment I put them together in any configuration the 5.25in drive starts misbehaving. The 3in drive has no problems ever.

I have narrowed down my configuration to really have only have one real problem. That being formatting of the 5in diskettes. Simply put... it does not work. I tried on the GUI and it didn't work with generic problems so I figured I'd go to DOS. I tried formatting normally using just /F:360 and despite succeeding it suggested that all sectors were bad and the visible area had a size of about 170kb. I then decided to try an unconditional format using /U and that had no impact. Lastly I tried /4 with /C to reexamine clusters and it said this:

Format complete.
Unable to write BOOT.
Format terminated.

It should be noted immediately afterwards I shut the system down and removed the 3in drive, restarted, and tried formatting the same diskette and it returned successful with zero bad sectors. I also tried removing the 3in drive in BIOS and keeping it attached and it seems that this doesn't work and results in a separate error stack:

Formatting 360K
Invalid media or Track 0 bad - disk unusable.
Format terminated.

This is untrue as formatting all the disks I have with the 5in drive alone succeeded with no bad sectors so I have no idea why this might be and I'd be super grateful for any help.

Reply 1 of 3, by DaveDDS

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You've already tried the first things I'd suspect, drive jumpers, twisted cable and terminations.

Next thing I'd probably check is power - do have an oscilloscope or at least a decent multimeter - I'd check that power supply voltages were still good (both +5 and +12) with both drive connected, and still no noise on them.

Another thing I'd try is the 3.5 at the end of the cable and no termination in the 5.25 - depending on the 3.5, it may have some "always" termination and if your FDC can't handle the extra load, removing term from 5.25 might help.

When booted to DOS, you can run ImageDisk - this might let you try some other things, and give you some more information. When doing so, try setting both drives to None in BIOS (ImageDisk talks to the FDC directly and does not use BIOS - setting to None can avoid "software interference").

With both drive connected, do they both physically operate as expected (motor on + seeking when accessed) - IMD align/test mode makes it easy to test things like this.

- Dave ; https://dunfield.themindfactory.com ; "Daves Old Computers" ; SW dev addict best known:
ImageDisk: rd/wr ANY floppy PChardware can ; Micro-C: compiler for DOS+ManySmallCPU ; DDLINK: simple/small FileTrans(w/o netSW)via Lan/Lpt/Serial

Reply 2 of 3, by Dolard

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Thank you Dave for the response! It seems as though it was a voltage issue. I guess the AT power supply I was using just couldn't hold steady enough for the 5in drive. Super grateful for your help in helping me solve this headache (:

Reply 3 of 3, by DaveDDS

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Good to hear it's working!

Seems odd though ... floppy drive doesn't need all that much power (original PC 5150 which didn't have a PSU anywhere near anything newer supported 2 x5.25)
Maybe the supply is "going" for other reasons, or perhaps something else in the system is causing excessive load - worth checking on.

- Dave ; https://dunfield.themindfactory.com ; "Daves Old Computers" ; SW dev addict best known:
ImageDisk: rd/wr ANY floppy PChardware can ; Micro-C: compiler for DOS+ManySmallCPU ; DDLINK: simple/small FileTrans(w/o netSW)via Lan/Lpt/Serial

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