(last updated: 08-Sep-2012)
The current configuration is in its original 'as acquired' condition.
| 1 | Video Board - 6800 w/ 48KB RAM |
|---|---|
| 2 | I/O Board - Z80A w/ 32KB RAM |
| 3 | CPU Board - Z80A w/ 64KB RAM + Disk I/O |
| 4 | I/O Distribution Board - x2 Serial Port |
31-Oct-1982
This date is more or less correct, but not exact. I purchased this machine from Novell Data Systems at the time of it's demise. Time things looked very dark for the company this time, but it later re-emerged as Novell, Inc. in January 1983
24-Jul-2008
While searching for some item that I now have forgotten all about I discovered that one of the boxes in my NDS 2010 stack had caved in a little on the rear and that the few things on stacked top were askew. I took a look and discovered that the boxes were damp! I pulled down the stack and found that there wasn't just dampness, but absolute wetness. The cardboard cartons were simply sopping wet and were falling apart. Mold had started to attack the cardboard, which tells me that this has been wet for some time, perhaps weeks.
The box that had caved in somewhat contained the disk drive subsystem, and unfortunately, because that particular box did not have a top piece of foam, water and gone directly into the box and pooled in the lower half of the molded surrounding foam. There was a good two inches of water trapped inside, and the disk unit was partially submerged in it. I had serious doubts about the viability of the system after seeing this.
I removed the disk subsystem, and drained the water from inside, out of the fan vent on the underside, and dried off the exterior as best as I could. At this point I wanted to get inside and actively dry everything rather than just let it dry on its own. The possibilities for corrosion are high when doing that.
So, I disassembled the entire unit, drying each and every piece. Two items are particularly noteworthy. First, the DTC controller PCB had been the first stop on the water's way into the system, and there was a thin film of water covering almost the entire board. The other is that the cooling fan in the lowest part of the subsystem's base had rusted solid and would not turn.
In the case of the controller PCB, I carefully dried everything with towels and absorbent paper, then I used my small air compressor with a narrow nozzle to blow the remaining moisture from underneath the integrated circuits and other components on the board. When dried completely, it is apparent that the water had begun to attack the epoxy layer on a good-sized section of the board which is no longer glossy, but dull. Several chips have rust stains on a two or three pins. I cleaned them as best as I could and hope that the pins are solid, and that there are no shorts between them. I checked a few worst cases with my multi-meter and found no short circuits.
As for the fan, after fully disassembling everything I was able to handle the fan alone and with a strong twist was able to break the spindle free. Once done, it spun surprisingly freely, and I hope it will still be operable.
After carefully drying everything I reassembled the subsystem, starting with the fan, then the power supply. With just those two items installed in the lower cabinet, I plugged in the AC cord to check the fan's operation. Fortunately, it works just fine and shows no negative effects from being submerged in water for who knows how long. I was worried that it would have become noisy with the rust developing inside, but I'm happy that this is not the case. It seems fine.
I continued the assembly, taking photos along the way. Once reassembly was completed, I see no lasting marks or damage. There are a few rust spots inside the cabinet from a few nuts and bolts, but everything looks just fine externally.
Now I need to checkout the rest of the system, and do an operational test to confirm that there is no real damage done.
24-Jul-2008
With the heavy and long duration exposure to water, all of the cardboard cartons that I've kept all these years are damaged too badly to try to use further. Besides, they are covered in mold and mildew, and I don't want them in my house! So, while it pains me quite a lot, I have decided to throw the cartons out.
Before they were taken away, I took the dimensions of each carton (CPU, Disk, Keyboard) in case I ever find cartons with the same dimensions which will allow me to properly pack and store the system again.
CPU: 25" L x 21-1/4" W x 23" H Disk: 22" L x 21-1/4" W x 18-1/4" H Keyboard: 24-1/4" L x 14-1/4" W x 6-3/4" H
I have kept all of the foam inserts, hoping for eventual success in finding replacement cartons, or making my own. The Disk Subsystem doesn't have a top foam piece at all, and I think that allowed the water to penetrate right into the system. I remember taking the original foam piece and slicing it up about 15 years ago to provide some cowl inlet plugs for my new Mooney MSE. Kind of a dumb thing to do, but I did it. It occurs to me now that if I do ever find some useable replacement cartons, I can make my own foam top by using some expandable-foam-insulation-in-a-can from the hardware store. Might require a couple of cans worth, but it should work just as well as the original. I should have thought of this before now, and I might have avoided water in the disk subsystem.
25-Jul-2008
Printer
First I looked over the Image 800 printer that had just a small amount of moisture on the exterior last night. Opening it up completely, I was very happy to find that there is no evidence of water inside the unit. Everything looks good.
I don't have the appropriate serial cable (have to make one) to connect the printer up to the CPU, but I did power up the printer and check what I could. The front panel is fine, working normally, but I have a problem with the carriage of the print head. There are about three points along the slide rails where everything binds up. With the power off, I can manually push through those spots, but the stepper isn't able to overcome the resistance. I can't tell if there is binding on the cable pulley, or on the rails themselves (they could use some lubrication). I'm inclined to think it is the pulley since the binding seems to occur at a certain point as the pulley rotates. I need to confirm this in the future, and see if it can be corrected. I might be due to the system sitting completely unused for 20 years.
CPU
When I made a quick examination last night this unit looked in good shape. I didn't see any evidence of water inside the carton, or on the surface of the computer. Still, I wanted to open it up and make sure. Besides, it gave me an excuse to re-acquaint myself with the insides of this old computer. I've never opened it up since I first got it, so I was pretty keen to refresh my memory.
I was overjoyed when I removed the top cover and found that everything was nice and dry and clean inside. That is great news! With that worry behind me I went to work disassemling the system, noting the major parts used, and then reassembling it. I did take a moment to power up the cooling fan with everything else disconnected from the power supply, just to confirm that it works. It does.
Most of the components and assemblies bear dates from 1981, but as was discovered during the power-on checkout, the firmware displays 1982 dates when initializing, so I consider this to be a '1982' machine.
Keyboard
Externally, the keyboard looked just fine. There was no water inside it's box last night, though the carton itself was a goner. I couldn't find a way to open the keyboard. There are no screws on the bottom, unless they are hidden under the rubber feet, but since the feet were strongly glued on I didn't want to take them off to find out. I could just peek through a small opening where the cord emerges, and everything looked just fine there, so I declared the keyboard okay.
25-Jul-2008
Now that everything is proven dry and clean, it's time to connect everything and test it. It's pretty simple, just plug the keyboard into the bottom front of the CPU, and connect the ribbon cable from the disk subsystem to the back panel of the CPU. Plug in the CPU and Disk AC cords and that's it.
Fortunately, there is no damage from the water! I powered the disk subsystem, and the hard disk spun up just fine. No sparks, smoke or duds. Then I powered up the CPU. It prompted for boot from floppy, and I typed 'N" and, lo!, the system booted from the hard disk, just as easy as could be.
So, it seems that the system has suffered no ill effects from the disk unit being in so much water. I'm glad I took the time to properly dry the controller board last night.
Well, I fiddled with CP/M for a few minutes (I can't remember much!), and eventually found my games 'user space'. I started ADVENTUR.COM and took a photo of the screen.
26-Jul-2008
Due to the long time since I used this system regularly, I had some trouble remembering some of the particulars of this system. After an hour or so I was able to re-learn a few thinks:
- CTRL+LOCK: resets/reboots the system - UPPER+CONFIGURE: enters terminal setup mode: - select character sets (glyphs) - configure serial ports - set TOD clock - Will first try to boot from floppy if prompt is not answered, and if no floppy in drive, will boot from hard disk - Boot the hard disk as drive A: - USER x changes 'directory' - STAT USR: shows with USER spaces are active - Novell's implementation of CP/M has unusual characteristics: - has 200 USER spaces, rather than usual 15 - has a 'public' drive N: which is like the search path, where CP/M and other executables reside - floppy drive is referenced as drive Z: - load keyboard keys files from N: before running WordStar and SuperCalc to enable function keys particular to each application
13-Aug-2008
While waiting on some PDP-11 diskette image processing, I thought I'd play STARTREK. Oh no! The system powers up fine, but the terminal computer doesn't recognize the disk subsystem anymore. It says "NO DISK OR NETWORK ACTIVE" and halts.
I can hear the ST-506 spin up, so it's alive, and both the floppy and harddisk LEDs flicker when I cycle the power, so each drive is powered. The other major component is the disk controller, which had some pretty heavy water exposure. I wonder if a chip, or PCB trace corroded out on me. Blast! How will I fix that? I have no schematics for the controller, so scoping it out isn't something I can do. I probably couldn't do it with a schematic anyway, but I sure can't try without it.
25-Aug-2008
While awaiting a response to my request to the classiccmp.org cctalk: mailing list hoping for anyone with a schematic to come forward, I sounded out the cable that runs between the disk subsystem and the terminal/computer. It's fine.
I checked the resistor packs on the CPU interface connector on the DTC520. They seem fine, all connector pairs giving a value of about 136 ohms.
I double checked the 8 position DIP switch and the readings are the same whether the switches are ON or OFF. There's obviously a interconnect via other components. I reset the switch all ON and all OFF to test, and I believe that have returned the switches to their original position with all ON, except 1 and 3. I need to review my photos to confirm that this is correct.
16-Sep-2008
A couple of things have happened in the past little while. First, I ordered several replacement chips from Jameco and DigiKey for some of the chips that are showing corrosion and rust on their legs. A couple of weeks ago I replaced the worst looking chip, a TI SN74LS33N in position 7K, but that didn't change the behavior of the system. All I get when booting the system is the same "NO DISK OR NETWORK ACTIVE" message on the terminal/computer.
Today, just to make sure the board is clean of any material that might be bridging contacts on chips or PCB traces, I removed the socketed chips (see below) and washed the board in the dishwasher, without any detergent. It came out looking somewhat better, and I let the board finish drying in the sun on the patio. Alas, when I put the chips back in, and connected everything up, I see the same old problem... "NO DISK OR NETWORK ACTIVE".
I'm thinking (worrying is more like it) that I might have to work up a schematic diagram, ala Tony Duell, by hand, and trace everything down. That is a ton of work, and I'm not sure that I'm patient enough to try it, let alone finish it.
Another thought is to continue with replacing the suspect chips one by one and just hope for a miracle. This is also tedious work that I might not have the patience for.
15-May-2010
On a lark I did yet-another-google-search and hit this:
http://stason.org/TULARC/pc/hard-disk-floppy-controllers/C-D/DATA-TECHNOLOGY-CORPORATION-Two-ST506-412-MFM-devi-262.html
which is for the DTC520DB, which I believe to be a later version of my DTC520. After looking at this I wonder if the trouble is related to the SASI addressing. No doubt the CPU BIOS is 'hardwired' for a particular disk subsystem address, and maybe the water infiltration corroded the selection switches, and then later as I was working with the board, I could have disturbed them without noticing, and only took my reference photos afterward. I think it might be worth a try to just test the SASA address switch block, and if it is good, try all different combinations of SASI address hoping to hit upon the correct one.
06-Sep-2012
I had a thought some time ago concerning this failure. Since the water 'damage' to the PCB is heaviest around the 8-position DIP switch, I thought that perhaps the contacts within it were corroded and thus failed. In order to test this theory I could remove the switch from the board, but instead I unclipped the board and turned it over so I had access to the solder side. Then I tested each switch with the system powered. The switch works fine in all eight positions, going on then off according to the position. So this idea has proved that the switch is working, but still doesn't solve the problem. For now, the system is going back on the shelf awaiting more ideas.
There is one option that now occurs to me. Somewhere along the way I have acquired a DTC-520D controller board, but at present I can't locate it. However, my thought is to disconnect all drives, swap that controller in in place of my DTC-520 and see if the main terminal computer at least recognizes that there is a controller there. Even so, it is doubtful that the controller would be able to read the drive, since the drive was not formated with that particular controller, but it just might be worth a try. Now, to find that controller; where did I put it?
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