Silent Q

Posted By azog on March 7, 2012

I’ve been browsing eBay for an enclosure for the P112 kit I recently built. It’s kind of hard searching for “external drive enclosure” because you end up with thousands of USB floppy drives. I could have installed it in a PC case, but that’s not very classy. I wanted it to look “different”.

I just decided to Google around until it gave me more ideas than eBay alone, and I found a good candidate in the form of an HP 9122 external HPIB drive.

I found a few of these listed on eBay with insane starting bids of like $200, even when blatantly non-working. I was quickly outbid on the ones that were “reasonable” in terms of price, until I found this 3rd party version of the 9122. It was posted with the infamous “tested, powers on” status, but I was more interested in the enclosure, power supply and possibly the drives. I didn’t care if the IEE488 interface worked or not.

It’s better, because if you look at an official HP 9122, they use funky floppy drives. This one looked like it uses PC style drives.

The rear view is pretty bland. An HP-IB interface and address switches, selectable voltage input and a fan.

Opening it up to assess the possibilities was encouraging.

It’s very well designed. Nice, clean layout. Everything looks modular. So I removed the floppy mounting bay to expose the controller board underneath.

Some interesting chips on there: a Z80, RAM and ROM, and a bunch of other stuff. I’ll set this controller aside. The controller is mounted on standoffs. Yet another bonus.

The floppy mounting bay is equally nicely designed. This is the view from the bottom.

They appear to be standard PC style 3.5″, 1.44mb floppy drives. Because of the mounting, I’m not too concerned about the drive functionality, as they can easily be replaced. But it would be bonus if they worked.

So now that I’ve got the controller and floppy bay removed, I can give it a once-over to see how to mount the P112 itself. The power supply stays, as it has a standard 4-pin Molex connector and two 3.5″ floppy power connectors.

The first test-fit shows only one of the mounting standoffs is in a suitable location. You can’t see it in this picture, it’s hidden behind the battery. I’ll have to move the other three.

Since I’m inept, this was the hardest part of the whole project. How to drill holes in the proper location? I found a 3.5″ floppy sled that had the right holes, so I used that as a template for drilling.

I wanted a reset switch, so I poked a hole right thru the front panel.

Build up a simple wiring harness, mount the P112, and test it. I also wanted to re-use the original power LED, but that was connected to the original controller, so I just soldered some random 120 ohm resistor to it, and connected it straight to the 5vdc supply.

I don’t know what to do with the P112 console cable, so I simply routed it loosely thru the now-empty IEE488 port. Again, ineptitude will prevent me from trying to cut a hole in the back panel to mount the console cable, and the P112 itself blocks me from kludge-fitting it to one of the empty screw holes.

So now it’s just down to the floppies and testing the whole thing. Since everything up to now went pretty smoothly, I figured it was a good time for something to go wrong.

Using the original two drive floppy system, I just connected them to the floppy header, but these original floppy drives don’t seem to work, or don’t work with the P112. I had a whole stack of other random floppy drives which I also tried. After about a week of trying every possible combination (single and/or double drive; single ended or double ended cable, with and without a twist, changing jumpers, etc), I got two drives to work, but neither has a bezel, which is unattractive but it tells me that things are generally operational.

I couldn’t really find any floppy drives for less than $20 on ebay, so I posted on a forum I frequently lurk. Someone mentioned an online retailer had 3.5″ floppy drives for $9. Sounded like a deal, so I ordered two for $22. I got them working, but I’m unhappy with them. Sometimes they seem to stop functioning. Maybe it’s related to this, below…

The P112 CD includes a variety of disk images. First I tried Z, but when it boots, the console says “OS loaded, booting…” and stops. I tried CP/M 2.2 with the same results. I ended up using the CP/M 3.0 image, which worked with an odd caveat.

At some point in the boot process, the console switched from 9600 to 19200 baud. You can see the baud rate on the status bar. I’ll figure that one out later…

Here it is all bolted back together. Can’t tell much of a difference from the original box, can you? Oh, and I make no apologies for the Hello Kitty. People who know me know I’m an unabashed fan of Kitty, and I decided to make her kind of a “signature” for completed, or semi-completed projects. You’ll be able to deal with it :)

I named this “part one”, as I still have to address a few issues:

#1 – What’s the deal with the original HP floppy drives?

#2 – Mount the console port. Actually I’d like to mount the “other” serial port, and perhaps the printer port too.

#3 – I’d like to eventually get a GIDE kit, at which point I’ll need to lose one of the floppies and all the above grief will be for naught.

#4 – figure out why Z and CP/M 2.2 won’t boot. UZI did, and so does CP/M 3.0. What’s the difference? I can READ the 2.2 disk while CP/M 3.0 is running, so it’s not a corrupt image.

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