VOGONS


First post, by DamienC

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I've done a fair amount of googling and I'm kind of stuck. I've been doing my annual messing around with old PCs and I'm having trouble with the 5.25" floppy in my 486/POD 83 build.

In a nutshell, I can read/write 1.2mb HD floppies perfectly fine, but this drive/machine won't read 360k disks at all. The floppy drive is a Teac FD-55GFR, my favorite 5.25" model and is set up to be drive B.

Computer specs:

  • Amptron DX-9500 aka PCChips M919 v1.5 (fake cache removed, 256k real cache added)
  • Pentium Overdrive P24T 83MHz CPU
  • 16mb FPM RAM
  • S3 Virge DX PCI 4mb
  • Sound Blaster 16 CT1740
  • IDE to SD adapter - 4gb SD storage
  • Allied Telesyn AT2000 10mbps Ethernet
  • AOpen 48x IDE CD-ROM
  • MS-DOS 7.1 (built from Win98SE disc)

I have this same floppy drive in two other machines: a 1991 Zeos 386SX with onboard floppy controller, and a Biostar motherboard 386DX computer with a generic ISA disk controller card. Both computers have a two-floppy drive setup with the 5.25" disk as drive B and they all read and write 360k disks just fine.

Unfortunately I only have enough room in my house for one vintage PC set up at a time, and I really want this jack-of-all-trades system to be the one I have set up for both gaming and also making disk images of all my old floppy based games.

Things I've tried that don't work (mostly based on Google results of similar issues):

  • Different floppy cables
  • Floppy drive swap in BIOS
  • Disabling all caches (L1 & L2)
  • Different autoexec.bat/config.sys configurations (clean boot, no EMS, etc.)
  • Cleaning drive heads

Things I still need to attempt:

  • Disconnect 3.5" drive A and just connect the 5.25" drive and see if issue persists
  • Swap known working drive from other system and test in this one and see if issue persists

I have a feeling this particular drive is just going bad. I hope to dig out one of my other floppy drives and throw it in this machine and see if it works, but I might not be able to do that for a couple days.

Is there anything else I could check in the meantime to figure out why this is happening? I know about the issues with 360k disks in 1.2mb drives, but I figured that mostly related to writing/formatting and I really just want to make disk images of 360k disks I have.

Thanks

Reply 1 of 7, by PCBONEZ

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~ This ~
[*]Disconnect 3.5" drive A and just connect the 5.25" drive and see if issue persists
[*]Swap known working drive from other system and test in this one and see if issue persists

DamienC wrote on 2019-12-31, 00:49:

Is there anything else I could check in the meantime to figure out why this is happening?

Not like often but (in forums) I've seen a few old FDD with bad capacitors show up lately.
Capacitors wear-out so that should more or less be expected with anything that old.
Fixing FDD is not my thing. I've never even tried to fix one.
.
Look for caps that are leaking or bloated but not all bad caps fail with visual indicators so that's no where near a 100% reliable.
.

GRUMPY OLD FART - On Hiatus, sort'a
Mann-Made Global Warming. - We should be more concerned about the Intellectual Climate.
You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.

Reply 2 of 7, by Horun

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PCBONEZ is correct about possible bad caps, there are about 7 and are very small 6.3 to 33uf(iirc) on the Teac 55GFR and a few handle the stepper and spindle motor. Many old floppy drives have been brought back by cap replacement and a good cleaning. It is odd that a DD 360k cannot be read because it has twice the track width as HD 1.2Mb. Usually it is the other way around where 360's work and 1.2's don't as the drive fails (from my experience). Are you sure the 360's are still good ? Over time the original magnetic recording dissipates on disks as it does on VHS tape and become unreadable.

Hate posting a reply and have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. 🤣 Second computer a 286 12Mhz with real IDE drive ! After that came 386, 486, Pentium, P.Pro and everything after....

Reply 3 of 7, by DamienC

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PCBONEZ wrote on 2019-12-31, 01:22:
~ This ~ [*]Disconnect 3.5" drive A and just connect the 5.25" drive and see if issue persists [*]Swap known working drive from […]
Show full quote

~ This ~
[*]Disconnect 3.5" drive A and just connect the 5.25" drive and see if issue persists
[*]Swap known working drive from other system and test in this one and see if issue persists

DamienC wrote on 2019-12-31, 00:49:

Is there anything else I could check in the meantime to figure out why this is happening?

Not like often but (in forums) I've seen a few old FDD with bad capacitors show up lately.
Capacitors wear-out so that should more or less be expected with anything that old.
Fixing FDD is not my thing. I've never even tried to fix one.
.
Look for caps that are leaking or bloated but not all bad caps fail with visual indicators so that's no where near a 100% reliable.
.

Well... I'm starting to think the drive is just messed up.

I took my other 386 out of the attic and yanked the 5.25" drive. I thought it was the same model, but it's actually an FD-55GFV. I'll refer to this as "good drive" and the FD-55GFR as "old drive." Results:

Good drive from 386 (prior to removal): Drive reads & writes all disks
Good drive in P83: Drive reads & writes all disks
Old drive from P83 installed in 386: Drive reads & writes HD 1.2mb disks, "Sector not found" when trying to read 360k disks
Old drive from P83 restalled in P83: Drive reads & writes HD 1.2mb disks, "Sector not found" when trying to read 360k disks

The drive doesn't appear to have any blown capacitors. It was sitting on a shelf in my non-climate-controlled attic for over a year, and I'm almost positive it was working fine back then. So I'm not quite sure what's wrong with it.

I'm just going to swap to the drive from the 386. Only slightly annoying thing is it has a black bezel and the other one is beige. I was sorta thinking of switching to a black case anyway.

Reply 4 of 7, by PCBONEZ

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Power it up.
Let it sit with power for about 2 hours.
Then try it.
.

GRUMPY OLD FART - On Hiatus, sort'a
Mann-Made Global Warming. - We should be more concerned about the Intellectual Climate.
You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.

Reply 5 of 7, by maxtherabbit

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I had a Mitsubishi 5.25" 360kB drive that would not read disks reliably at all. None of the electrolytics on the board had any visible bloating or leakage, yet when I removed them I found some with almost no capacitance remaining. After a recap the drive works fine.

Reply 6 of 7, by PCBONEZ

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Yes.
Only -SOME- bad wet-lytic caps bloat or leak.
All of them eventually wear out.

Aluminum Electrolytics are (used to be) called "Self Healing" caps.
With a DC bias applied the oxide layer will rebuild itself and repair any damage to the layer.

When caps sit with no DC voltage applied the layer gets thin by slowly dissolving back into the electrolyte.
There is a point where enough dissolves that the cap will not work right.
If you then put voltage on it a process like electroplating occurs that rebuilds the layer. - Then it works again.
- All of that only works until the electrolyte wears out from age, oxidation and/or contamination.

This is why I said to put power to it for a while then check again.

This is also why you should power-up any stored boards (cards & mobos & FDD too apparently) with wet-lytics for at least 1 hr a year.
30 minutes is probably enough for 1 year, just failing-safe by saying 1 hr.
.

GRUMPY OLD FART - On Hiatus, sort'a
Mann-Made Global Warming. - We should be more concerned about the Intellectual Climate.
You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.

Reply 7 of 7, by SirNickity

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Bloating and leaking tends to come from overheating. Often, internally-generated heat, which is common with caps that are applied across power rails. (Leaking can also occur because of material failure at the bottom rubber seal.)

Now, electrolytic caps are also used for signal conditioning -- like DC-blocking. In this case, they'll be exposed to very little current, and so will not heat up enough to expand and swell. I just recovered a 720KB Teac 3.5" drive by replacing its caps. They looked perfect, but one measured 0uF. So, if you can, give it a shot -- nothing to lose.