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Strange floppy drives issues

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First post, by aha2940

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Hi guys

Recently I received an AI5TT socket 7 board (manual here: http://www.elhvb.com/mobokive/archive/Tmc%20- … ual/AI5TT12.PDF). I have tested it, and so far it *seems* to be working fine. I've tried the AT keyboard port, ps/2 mouse port, USB ports, both IDE channels and *floppy* port. Now, I also have 4 floppy drives. 2 known working, and the other 2 were a gift in unknown condition, I had never tested them, nothing strange. I tested them with this socket 7 board, and they throw "General failure reading drive A:". I was told in these forums that this was not something I could solve by cleaning the heads, and drives were dead. Bad news I guess. So, I plugged a known-working drive to the board. I used it to successfully install DOS 6.22 on the socket 7 PC, and copy a couple files from another PC I have. Now, I just tried to copy some more files, and the drive is also throwing "General failure reading drive A:" errors. I didn't even shutdown the machine since it was working fine!! I just copied the soundcard driver, it copied OK, then I went to my other PC, copied some more drivers and BAM! now it won't read any disk. So, my questions are:

- Can something inside the board be damaging the drives?
- Maybe the Winbond W83977TF controller is bad somehow?
- I am afraid to try my last working drive there, I do not want it to get fried too.
- Am I being paranoid and it is just bad luck / coincidence?

I do not think the power supply is bad, since no other components are even acting up, and I do not think the floppy would be the most delicate component here.

Any thoughts / ideas / opinions are appreciated, thanks.

Reply 2 of 10, by aha2940

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appiah4 wrote on 2020-03-21, 18:07:

Do the supposedly bad drives work in other PCs, have you tried this?

Yes, I forgot to mention it. The drives do not work in other PCs I tried them, they seem to be in fact damaged.

Reply 3 of 10, by Horun

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aha2940 wrote on 2020-03-21, 19:02:
appiah4 wrote on 2020-03-21, 18:07:

Do the supposedly bad drives work in other PCs, have you tried this?

Yes, I forgot to mention it. The drives do not work in other PCs I tried them, they seem to be in fact damaged.

Check the PSU voltages. If the +5 and +12 are above or below by 0.5v or more it could do some damage. Most motherboards can tolerate questionable PSU better than 1.44Mb floppy drives can.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 4 of 10, by aha2940

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Horun wrote on 2020-03-21, 19:16:
aha2940 wrote on 2020-03-21, 19:02:
appiah4 wrote on 2020-03-21, 18:07:

Do the supposedly bad drives work in other PCs, have you tried this?

Yes, I forgot to mention it. The drives do not work in other PCs I tried them, they seem to be in fact damaged.

Check the PSU voltages. If the +5 and +12 are above or below by 0.5v or more it could do some damage. Most motherboards can tolerate questionable PSU better than 1.44Mb floppy drives can.

Thanks for the suggestion. I measured the voltages under load (PC running), but both are within the limits, so I don't think the PS has problems.

Reply 5 of 10, by Horun

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Hmm it is possible that there is a short in the floppy bus causing the +12 or +5 to hit the data lines. Check (with no floppy drive connected) the volts on all the even # pins on end of the floppy cable.
This page lists what each of the pins are for: http://www.interfacebus.com/PC_Floppy_Drive_PinOut.html

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 6 of 10, by aha2940

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Horun wrote on 2020-03-21, 23:30:

Hmm it is possible that there is a short in the floppy bus causing the +12 or +5 to hit the data lines. Check (with no floppy drive connected) the volts on all the even # pins on end of the floppy cable.
This page lists what each of the pins are for: http://www.interfacebus.com/PC_Floppy_Drive_PinOut.html

Thanks for the suggestion, however I'd like to understand better: If I turn on without a floppy drive connected, it's because I had to disable it in the BIOS, but if I disable it, why would there be any voltage on the data lines? I don't get it...

Reply 7 of 10, by Horun

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Actually you should not have to disable in BIOS, just leave the floppy cable connected to mobo, it should just give an error like Press a Key to continue. You are looking for a full 5V or 12v on the data lines which NEVER occurs because they are clocked so should not show same as your 5+ or 12+ PSU lines.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 8 of 10, by aha2940

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Horun wrote on 2020-03-22, 01:51:

Actually you should not have to disable in BIOS, just leave the floppy cable connected to mobo, it should just give an error like Press a Key to continue. You are looking for a full 5V or 12v on the data lines which NEVER occurs because they are clocked so should not show same as your 5+ or 12+ PSU lines.

Hi!

I just did this test and had the following results:

* All odd pins are grounded (as expected, according to this pinout: http://www.interfacebus.com/PC_Floppy_Drive_PinOut.html)
* All even pins have no voltage (0V, or a voltage so tiny that it barely moves my voltmeter's needle), *except* for the following pins which have +5V:

- Pin 8 -> /INDEX
- Pin 26 -> /TRK00
- Pin 28 -> /WPT
- Pin 30 -> /RDATA
- Pin 34 -> /DSKCHG

There are no voltages different from 0V or +5V on any pins. I have no idea if these voltages are normal or not, or if they are due to measuring with the floppy drive disconnected.

Thanks for the help 😀

Reply 9 of 10, by Horun

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Those pins carry signals to the floppy and should be about 4.6-4.7v (or about 0.3-0.4v less than the 5V+ supply voltage. Do you have a digital Voltmeter ?

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 10 of 10, by aha2940

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Horun wrote on 2020-03-23, 22:32:

Those pins carry signals to the floppy and should be about 4.6-4.7v (or about 0.3-0.4v less than the 5V+ supply voltage. Do you have a digital Voltmeter ?

Unfortunately, I only have an analog voltmeter that works. I have a digital one, but it's broken, since it measures way too high any voltage. for instance, it measures around 6.3V on the output of a PC's PS +5V and it measures about 200V AC on the wall output, however in my country the wall output gives 115V AC. It's a crappy digital voltmeter. However 0.3-0.4V does not sound too bad, do you think that could have damaged the floppy drives?

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