Hitachi FDD-412A 8 inch floppy drive

[mk2s]

It's August 2026 and I've come into a FDD-412A by way of a disk duplicator on a Japanese auction site.

I'm trying to verify that the drive is operational and found this thread. I see that @someoneontheinternet mentions he found the "service manual" at The Internet Archive, but I've been unable to find this. If you have a copy or know how to find it please let me know.

My drive came without terminating resistor, but I've found a replacement.
I've attached pic of my jumper setting. According to what I've read this means VFO source is disk, VFO output enabled when drive is selected, and decoded VFO to pin 33. Mine does not have jumpers between J1:7&8 while others like @valcanaria have that jumper. Wondering whether that might be termination related.

fdd412a_jumpers (1).png (137.59 KiB) Viewed 704 times

....maki....

[Vulcanalia]

You can find the manual easily: its the SHARP FDD 412A
https://www.manualslib.com/manual/32924 ... -412a.html

Working on the data separator still. i have a nice VFO signal from the SED9420 but it can be shifted 180 degrees , which makes it hard to get the pulses correct.

[mk2s]

Thank you so much Valcanalia. That's super helpful, and confirms J1:7&8 for termination. I was searching for Hitachi so maybe that's why I couldn't find it. If I get to making a 34pin adapter I'll share my board. The unit I got also came with a YD-380 model 1713 which is a 5.25" 1.2Mb drive with 50 pin connector just like the FDD-412A and also with a VFO. I've been working through issues on that drive like non-functioning index pulse.
....maki....

[Vulcanalia]

Hi Maki,
Excellent, good to have you on the team!
From the picture of the FDC board by "WhoSoldItToMe" it seems that the separated data is just simply combined in the FDC.
That would simplify the job to create just the proper pulsewith centered around the VFO.
Thats my current approach.

Is your goal to get the emulator running?

I want to get the emulator working, figure out how the okuma file system is set up, and then convert my 8" files to a 3,5" format, readable by OSP software. So that i then can run my OSP5000 system on MBII hardware (CMOS memory instead of Bubble).
Would be wiser to buy a newer lathe, but hey, its also an intest for fun.

[mk2s]

Is your goal to get the emulator running?

My goal is to verify/fix this drive to end up with a working drive. I may even sell the drive after validating it. I am a bit interested in getting the emulator running, but don't have the OSP5000 so can only make suggestions.

i have a nice VFO signal from the SED9420 but it can be shifted 180 degrees , which makes it hard to get the pulses correct.

I would think the job of the data separator is to separate correctly all the time. So if it's not 100% you'll need to figure out when/why. You may need to adjust something on the data separator side. Also reading the history of posts here if I understand correctly the OSP5000 8" disk has FM on track0 and MFM on remaining tracks. This is not uncommon on 8" media. I know of old CP/M machines that can only read FM on track0 to boot. But this affects the data separator as it takes as input the modulation see pin10. However I think the OSP5000 FDC also puts out a signal called MFM Gate that indicates this so maybe you can use that.

....maki....