The HP 9895 is a dual 8" floppy disk unit, which talks to the host computer via HP-IB. It's a great companion to the HP 9825 scientific calculator, but it connects to a very wide variety of HP computers, including HP 1000 series and the HP 85.
Internally, the disk drives themselves are CDC drives, model BR8A8B. None of the ones we had did work, some with electronic faults, most with belt and bearing faults, and all with a broken brake in the head position motor. You can connect these drives directly to an older PC by the way, without the need for the HP-IB contoller board.
That led us to a deep dive into 8" floppy disk and their many differences, as well as similarities, to more modern 5-1/4 and 3.5" brethrens.
Some of our HP-IB controller boards had failed too, but we repaired them all, while reverse engineering them while we were at it.
We restore our first CDC BR8A8B and learn all about 8" floppy drives, including connecting them to a PC using an adapter developed by my friend Antoine, available at: https://www.tindie.com/products/jurassicomp/8-floppy-disk-interface-50-pin-to-34-pin-adapter/
Here we show the complete 8" diskette drive restoration procedure, including replacing broken brakes with a 3D printed part, belt replacement, and going through drive head alignment.
We repair the first HP 9895 dual disk drive unit and use it to play Colossal Cave
We repair two HP 9895 controller boards and reverse engineer them while we are at it.
They are available on Tindie, here is a link to Antoine's store
https://www.tindie.com/products/jurassicomp/8-floppy-disk-interface-50-pin-to-34-pin-adapter/
Refer to the "All you never wanted to know about 8" floppies" video to find out how to set them up.
Most of our drives had the brake part fail in the stepper motor.
A step file to print out a replacement is here:
https://drive.google.com/file/d/1R1JfgcCpUcura-fH2WtWzi3PewHuyY4X/view?usp=drive_link
We ordered our replacement from PCBWay, so it could be made of a very strong reinforced material
Refer to the "8" Flppy Drive Final Repair" video to see how order and replace the brake.
The HP 9825 supports two 8" floppy disk drives, the HP 9885 and the HP 9895. These are far faster, more reliable, and larger capacity than the DC-100 tape drive included in the unit.
The HP 9885 is a single drive, single sided, single density floppy, and connects via a parallel 16-bit IO interface.
The HP 9895 is a dual drive, supporting both single and double sided, single and double density floppies, for up to 1.2MB of storage. It connects via the HP-IB interface plug-in (which must be either a Revised A or a B model, the original A won't work).
But in order to use either of these drives, you'll need an HP 98288 Mass Storage ROM. And these are as rare as hen's teeth. And they were thought to be difficult to duplicate, since HP used proprietary mask ROMs with some very unusual address decoding, bank switching and power logic embedded in them.
But that all changed when Paul Berger got his hands on an equally rare SSS Mass Storage ROM, which my friend Jack Rubin had acquired. SSS was non-HP, but they were obviously former HP engineers from the 9825 development team with very deep insider knowledge. They made an upgraded Mass Storage ROM that supported the newer 5.25" and 3.5" HP-IB drives, at the expense of dropping support for the older HP 9885 drive.
Paul reverse engineered the boards and found that SSS had used standard ICs and two Intel 2764 EPROMs to make an HP ROM equivalent. The only slight difficulty in the design is that it also includes a small bipolar 82S129 PROM, which does not contain code, but is instead used to implement address decoding. So you have to program 3 ROMs to make this work: the two 2764 EEPROMs that contain the same code as the original HP ROMs or the SSS ROMs, and the little 82S129 with a small binary image.
Once Paul had reversed engineered the SSS design, a copy of the SSS PCB was made by Adrian Nicol, and a make-your-own Mass Storage ROM clone solution became available to the community. You could flash the two 2764 EPROMs with the SSS or the original HP 98288 images. It was soone realized that if you used 27128 instead of the 2764, and slightly modified the board with a switch and a resistor, you could burn both images on the larger PROM and select which one you wanted to use with the switch. That's what I did on my board, and I include explanations on how to do it in my notes in the files below.
The info to make the clone is available below, except for the Gerber of the PCBs, which I could not find. But KiCAD schematics are included as well as images of both sides of the original SSS PCBs, so making a new PCB should be relatively straightforward.
I listed all the individual files below so you can browse around, but I also included a .zip file that has all the files in it so you can download the whole package with one click.