FC9801 computer FDD replacement

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Vector
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FC9801 computer FDD replacement

Post by Vector » Mon Nov 22, 2010 9:04 am

Hi,
I am new to this forum. I have aquired a Japax wire cut EDM machine and am having troubles with the FDD. I would like to convert to a FDD emulator as the disks are now almost always faulting when read.

The computer running the machine is a NEC computer type FC9801. It has 2 FDD type NEC FD1135D.

I have managed to read disks using "Omniflop" and have determined the following; The FDD runs at 360 rpm. The disk has 77 tracks, 2 sides, 26 sectors, 256 bytes per sector and is encoded MFM with the exception of the first track which is FM and has 128 bytes per sector. It is this last part which may cause trouble.

I have managed to get identical disk images off 2 disks of the 7 disks I have and hopefully I will be able to transfer that to a SD.

Will this emulator work for my particular disks ?
Chris P

Jeff
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Re: FC9801 computer FDD replacement

Post by Jeff » Tue Nov 23, 2010 9:55 pm

Vector wrote:Hi,
I am new to this forum. I have aquired a Japax wire cut EDM machine and am having troubles with the FDD. I would like to convert to a FDD emulator as the disks are now almost always faulting when read.

The computer running the machine is a NEC computer type FC9801. It has 2 FDD type NEC FD1135D.

I have managed to read disks using "Omniflop" and have determined the following; The FDD runs at 360 rpm. The disk has 77 tracks, 2 sides, 26 sectors, 256 bytes per sector and is encoded MFM with the exception of the first track which is FM and has 128 bytes per sector. It is this last part which may cause trouble.

I have managed to get identical disk images off 2 disks of the 7 disks I have and hopefully I will be able to transfer that to a SD.

Will this emulator work for my particular disks ?
Have a look to this thread :
http://torlus.com/floppy/forum/viewtopic.php?t=455

Yes these formats is supported BUT if the FC9801 need the "window" and "sync" signal from the disk drive this can be a problem.

floam
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Re: FC9801 computer FDD replacement

Post by floam » Wed Sep 21, 2011 3:37 am

We just ordered a couple units as we have two of these Japax EDMs we want to convert. Did you have success?

Jeff
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Re: FC9801 computer FDD replacement

Post by Jeff » Wed Sep 21, 2011 7:27 am

floam wrote:We just ordered a couple units as we have two of these Japax EDMs we want to convert. Did you have success?
You will probably need an additionnal board for the VFO.

What is the floppy disk drive used ?

floam
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Re: FC9801 computer FDD replacement

Post by floam » Wed Sep 21, 2011 8:17 am

The computer is connected to an external FDD box with two NEC FD1135D drives in it.

Inside, there's one regular FDD connector on a circuit board with mostly 74-series chips on it that goes to the two drives. There's two regular FDD power connectors, and also a wire that runs to a jumper on top of each floppy drive. Not sure what it does. Only one of the ports on the back of the external chassis goes to the computer.

What will I need to buy?
Last edited by floam on Mon May 28, 2012 1:59 am, edited 2 times in total.

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Re: FC9801 computer FDD replacement

Post by Jeff » Thu Sep 22, 2011 11:49 pm

floam wrote: What will I need to buy?
In fact as far as know there are no vfo board available "ready to use".
Some people have successfully used the HxC with an vfo ( http://www.gamepres.org/?p=83 ), but i don't know where they got it.

Anyway maybe that the EDM doesn't need the vfo. can you take a picture of the motherboard (fdc part) ?

floam
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Re: FC9801 computer FDD replacement

Post by floam » Fri Sep 23, 2011 12:22 am

Image

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Re: FC9801 computer FDD replacement

Post by Jeff » Fri Sep 23, 2011 7:47 am

Thanks.

And inside the FC9801 ? a picture of the FDC part of the computer ?

floam
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Re: FC9801 computer FDD replacement

Post by floam » Fri Sep 23, 2011 7:54 am

Don't have that with me. I can get one tomorrow for you. Thanks for the help.

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Re: FC9801 computer FDD replacement

Post by Jeff » Fri Sep 23, 2011 11:13 am

floam wrote:Don't have that with me. I can get one tomorrow for you. Thanks for the help.
And a picture of the floppy disk drive PCB if possible.

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Re: FC9801 computer FDD replacement

Post by Jeff » Wed Mar 14, 2012 11:18 pm

There are now a board with the famous VFO circuit :

http://kitahei88.dtiblog.com/blog-entry-94.html
:wink:

Image

floam
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Re: FC9801 computer FDD replacement

Post by floam » Sat May 19, 2012 7:09 am

Sorry, I ended up putting this project on the back burner. Here's various photos I took a while back. Hard to get inside, I hope this may help. Can't remember which if any of these were of the relevant area. I suppose I will just move forward without the VFO thing and see if it works. I will take some pictures of the old FDD PCBs.

Photo Sep 23, 1 05 34 PM.jpg
Photo Sep 23, 1 05 41 PM.jpg
Photo Sep 23, 1 05 53 PM.jpg
Photo Sep 23, 1 06 02 PM.jpg
Photo Sep 23, 1 06 26 PM.jpg
Photo Sep 23, 1 06 50 PM.jpg

Jeff
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Re: FC9801 computer FDD replacement

Post by Jeff » Sat May 19, 2012 8:35 am

I don't see any VFO chip on these pictures, so you will probably need the additionnal VFO board.
Let me check if there are some available.

floam
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Re: FC9801 computer FDD replacement

Post by floam » Sat May 19, 2012 10:01 am

Thanks. Definitely interested in getting one, maybe a spare if I can afford it. Looks like I could probably place a digikey order and clobber one together but that board would be very slick.

floam
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Re: FC9801 computer FDD replacement

Post by floam » Sun May 20, 2012 4:40 pm

and also a wire that runs to a jumper on top of each floppy drive. Not sure what it does.
By the way, these (white wires in my photo of the NEC dual floppy box) run to the RD header on each of the floppy drives, this enables VFO/VCO. Indeed inside the floppies there are 19.2 MHz and 16 MHz oscillators right near these pins just like kitahei88's circuit.

Should it be better to use the HxC through the interface inside the dual-drive enclosure or going directly to the computer? I don't quite understand if these wires are enabling this in response to detected SYNC/WINDOW commands and superflous for HxC+VCO circuit purposes (but maybe helpful for me to find out if the computer is sending these commands) or what.

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