Re: 26 pin MFM drive

On 11/5/2021 4:08 PM, philo wrote:
> In my box of obsolete computer parts, I found a JVC   LD3824R00-1   20 Meg MFM drive. It has a 26 pin connector and no separate power pins.
> 
> 
> No idea where it came from. Does anyone know anything about this drive?
> 
> 
> It's the same size as a standard IDE drive.

The disk drive industry, must have been a train wreck
at some point. There used to be a lot of disk drive companies.
JVC was one of them (so not just a rebranding exercise).
At first I thought, if it was made by someone else, we'd
need to figure out who that was.

https://en.wikipedia.org/wiki/List_of_defunct_hard_disk_manufacturers

*******

Badcaps.net has a thread for this. This is the text from the PDF
file in one of the attachments---

The JVC JD-3824R00-1 harddisk

This is the internal hard disk of a Toshiba T-3100. It uses a
custom interface, probably similar to the ST-506 harddisk interface,
but fewer pins. Both signals and power are combined in one 26 header.

Other machines using this type of hard disk interface:

Epson PX-16
Epson Equity LT
Epson Portable PC (Q150A)
Sharp PC-7200
Data General One Model 2T ?
GRiDCase 3 Plus
Toshiba T1200 ?
Wang WLTC Laptop

3. Parameters (2 heads, 34 sectors, 615 cylinders)
4. 2-7 RLL coding
5. Spindle Rotation: 2597 rpm
6. Data Transfer: 7.5M bps
7. Average Access: 78ms
8. Power Voltage: 5V and 12V

This is the controller from the Toshiba T-3100. The chip numbers are: T7518 (large one), DC2090P166A
(smaller one), TC57256AD-20 (EPROM). All are of the Toshiba brand.

Pin 1 GND (20- 2)                   Pin 2 -Read Data (20-18)
Pin 3 GND (20- 4)                   Pin 4 -Write Data (20-14)
Pin 5 GND (20- 6)                   Pin 6  Reserved
Pin 7 -Drive Select/+Power Save (-) Pin 8 -Ship Ready (-)
Pin 9 GND (20- 8)                   Pin 10 +Read/-Write control (34- 6)
Pin 11 -Motor On (-)                Pin 12 Head Select(+Head 0/ - Head1) (34-14)
Pin 13 -Direction In (34-34)        Pin 14 -Step (32-24)
Pin 15 -Write Fault (34-12)         Pin 16 -Seek Complete (34- 8)
Pin 17 -Servo Gate (-)              Pin 18 -Index (34-20)
Pin 19 -Track 000 (34-10)           Pin 20 -Drive Ready (34-22)
Pin 21 GND (20-11)                  Pin 22 +5V (-)
Pin 23 GND (20-12)                  Pin 24 +5V (-)
Pin 25 GND (20-15)                  Pin 26 +12V (-)

The signals have the same name as the ST-412/ST-506 interface (between'()'),
but the read/write signal is not differential.

*******

This is the badcaps.net page where I got the PDF dump in
the previous section.

https://badcaps.net/forum/showthread.php?t=64108

The two JPGs. Reposted via Postimage.
Use the "Download original" to get full res (3000x1688 using bad quality lens).

One is a picture of the Toshiba adapter board, which
appears to convert from one useless standard (26 pin) to
another useless standard (34 pin). It was popular in those
days, to throw a thousand dollars worth of electronics
at a simple serial stream. Mainly, because the boards
might be available in some catalog, and you "just buy them"
rather than wasting time on more engineering effort.

    https://i.postimg.cc/VvynLk0b/20170824-190914.jpg

    https://i.postimg.cc/VLWnm1fd/20170824-190846.jpg

One of my guys at work did that. That's why my best
guess at the design, is it was a "catalog engineering job",
joining one defacto standard to another.

      Paul