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Help connecting a Hitachi HFD305SD 3" floppy drive to a PC

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First post, by popcalent

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Hi, all.

I'm trying to connect a Hitachi HFD305SD 3" floppy drive to my 386 PC. This particular drive uses a 34-pin shugart edge connector and a molex power input, as opposed to most 3" drives that use a 26-pin header connector. I thought (maybe I read it somewhere) that these drives are 100% compatible with 180K/360K drives, so I was about to connect it to my PC, but then I thought I would check the power input with a voltmeter in continuity mode. Regular 3" floppy drives have the 12V/5V pins swapped, but this one should not. Another thing is that regular 3" drives use the small molex connector (same that goes to 3.5" drives) and this one uses the big one that goes to 5.25" drives. Anyway, to confirm the power input with the voltmeter I checked the continuity between the two positive input pins, and the pins of a few ICs that are on the board. The one where the 5V go is not in continuity with any IC pin, and the one where the 12V go in is, which makes me think the 5V/12V pins are reversed (the two middle pins have continuity so I assume they are both ground). I don't have access to any exposed pin of the motor to check continuity with the power input pins. I need to confirm what pin is what because I don't want to fry the drive.

I found a manual here: https://library.defence-force.org/books/conte … del_hfd305s.pdf, but it shows a block diagram of everything, including power, and it doesn't tell what corresponds to what in the molex connector.

As I'm writing this post, I found this page: https://atari-owner.com/club/resources/hitach … ad-sinclair.71/ that says the 5V/12V are not reversed in respect to a PC (see picture), but again, I find it weird that the Vcc of the different ICs is directly connected to 12V, and not 5V.

Help, anyone? Thank you!

hitachi_hfd305d.jpg
hitachi.png

Reply 1 of 3, by wierd_w

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A normal 5.25 capable ribbon should work?

(Example product. Not an endorsement)

https://www.amazon.com/CablesOnline-24-inch-U … n/dp/B07KDJTMGP

Attach it after the twist for drive A, and before the twist for drive B.

The computer wont/shouldnt care about which connector (idc / card edge) the drive is on, as long as the signal pinout is correct.

Molex power cables have the ground pins on the center pair.

IA43b.jpg

Verify orientation of the receptacle against your measurements.

Reply 2 of 3, by DaveDDS

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If it's the same as a 5.25" connector (seems odd for a 3" drive) then you should be able to use any 5.25" compatible floppy cable.

If it's not, you'll have to find or make one. (I've got adapter between 5.25"<->3.5", Desktop3.5"<->Laptop3.5" and 8"<->5.25" - most of these are "off the shelf" but I did have to make the 8" one, it's not tough!

As for power, you'll have to confirm the correct ordering, if you can get a datasheet on the drive, that would be best, but it's usually no to hard to "figure out".
5v will go to logic. 12v will go to "switch" ICs and then to motors, steppers and solinoids.

- 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 3 of 3, by wierd_w

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I see '+12' silkscreened right on the pcb, right on the molex connector.

When compared with the port's orientation, this matches standard molex power?

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