Computer Room

Computer hardware and software; especially vintage machines and retrocomputing.

Jul 292014
TRS-80 Model 1

Well, I’m finally the proud new owner of a TRS-80 Model 1 system! I just bought it on eBay for the princely sum of $380.85 including shipping. Yes, I’m geeky enough to take pleasure in the presence of "8085" in that amount.

Here are the eBay listing pictures, used with permission from the seller. I’m looking forward to seeing it in person, because I haven’t touched one since around 1979 or so, and back then I didn’t know anything about computers. My first computer experience came with a TRS-80 Color Computer a year or two later, and I never got any experience with the Z-80 TRS-80s until I became interested in retrocomputing less than a year ago.

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Jul 132014
Chalco Paper Tape Reader

I just bought this punched paper tape reader through eBay, just because it looks neat. It was made by Chalco Engineering Corporation, and the accompanying paperwork indicates that it was part of the AN/TPN-19 radar system. It appears to have been overhauled and then packed up for use as a spare. I didn’t find any technical details about it online, but to my amazement I found an original manual for this series of tape readers in another eBay listing! The manual doesn’t cover all of the details of this particular model, but it should be very helpful anyway. When I get around to it, I’ll scan the manual so it can be archived online somewhere.

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Jul 062014
New Life for a TRS-80 TP-10 Printer

The little Radio Shack TRS-80 model TP-10 was a thermal printer with a serial interface, formerly sold for use with machines like the Color Computer. They show up on eBay from time to time, sometimes for very few dollars. They’re small and quiet, and suitable for utility printing such as when developing BASIC programs. You wouldn’t want to turn in a book report printed on one, but they’re fine for utility purposes. I got mine for next to nothing as a ride-along with some other items in an eBay lot. It had a bit of paper left in it, but the paper appears to have weathered a lot of hot summers in somebody’s garage, and it doesn’t give very good print quality any more.

Unfortunately, paper for the TP-10 isn’t so easy to find. They use 4-1/8" wide thermal roll paper, which doesn’t seem to be a common size in the US at this time. When original TP-10 paper shows up on eBay, it’s listed at $10 a roll or more… I think I paid about that much for the whole printer! I decided to try an experiment to see how easy it would be to cut down common (for the time being…) FAX machine paper.

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Jul 062014
A Paper Tape from eBay

With a nudge from Earl, one of the RCR Podcast guys, I bought this punched paper tape from an eBay listing, described as "STRTRK (Startrek)" on paper tape for Imsai/Altair/S100/8080/Z80 etc. I don’t presently have any S100 type machines, but it looked interesting to me anyway. The seller had no knowledge of what was actually on the tape, so it might have contained machine code, source code, documentation, or something entirely unrelated to the label.

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May 292014
Nothing Sucks (Power) Like a VAX

I’ve wanted a VAX-11 system for a while, and now I have one! I bought this VAX-11/730 system from a seller in Wisconsin on eBay. It includes 4M RAM, an R80 fixed hard drive, and RL02 10M removable pack platter hard drive, and a TU80 tape drive. The CPU cabinet also includes a couple of TU58 DECtape II drive; one on the front panel, and the other on the right side of the CPU cabinet, accessible when it’s slid out of the rack.

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Mar 082014
Data General Nova 3 and DEC PDP-11V03-L

Back in February, I was contacted by somebody who found my web page and thought I might be interested in some old computers in his company’s basement. The company turned out to be in Culver City, within reasonable driving distance from my home in Riverside, and I ended up purchasing both of the computers. One is a Data General Nova 3, installed in a rack cabinet with a hard disk drive that has one fixed platter and one removable platter. The other is a Digital Equipment Corporation (DEC) PDP-11V03-L, which is a combination of a PDP-11/03 and an RX02 dual 8" floppy drive mounted in a short rack cabinet.

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Feb 072014
Look at what UPS Brought Me Today!

Fresh off the truck comes this exciting eBay find: A Digital Equipment Corp. (DEC) PDP-8/M! According to the seller, this particular machine originally controlled some sort of industrial sewing machine. The board numbers tell me that it should have 8192 words (12 bits each) of core memory. I’ll mate it up with my recently-acquired Teletype Model 33 ASR (commonly but incorrectly called an "ASR-33") which will provide a printing terminal with low-speed paper tape reader and punch.

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Feb 072014
A Silly Paper Tape Renderer

When I first became a cryptographic hardware collector, Mark’s Green Pages was a simple static-HTML web page. It started off as Mark’s Green Radio Page, and then turned into Mark’s Green Pages with sub-pages for radios and trucks. So when I wanted to add cryptographic hardware to the mix, I naturally created a new sub-page called Mark’s Crypto Page. I wanted a page banner that captured the essence of the mechanical and electromechanical cryptographic hardware that interests me, and I came up with this title image that melds together M-209-like printed text with Fialka-like 5-level punched paper tape:

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Jan 182014
DEC VT240 Terminal

Here are some pictures of a Digital Equipment Corporation (DEC) VT240 terminal with a VR201-C amber monochrome monitor. It’s just about to be sent away as part of a trade deal. I’m posting the pictures here to show them to the collector who I’m trading with, and then I’m leaving them here because there’s always room for more pictures of cool old computer equipment on the Internet. I took the pictures on the tailgate of my truck because it was the only free spot I could find to set the terminal down. :)

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Jan 032014
DEC RL02 Drives

Here are some pictures of my new heap of old Digital Equipment Corporation RL02 hard disk drives. They store 10 megabytes on a removable 14 inch platter. I’ll be using some of them in my PDP-11/44 project. I don’t have much to say at the moment… I’m mostly just posting these so I can refer to them in mailing list discussions.

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Nov 242013
Version 2 of TRS-80 Model 4 ROM Adapter

I previously designed a small adapter board to allow a regular 2764 EPROM to be plugged into a TRS-80 Model 4 (Gate Array version only) in place of ROM chip U4, in order to use the new auto-booting feature of the FreHD hard disk emulator. As I posted earlier, the assembled board was a bit too tall to fit under the aluminum shield that is present on US Model 4 computers, and it also needed a couple of pull-up resistors added. I changed my board design to address these problems.

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Nov 042013
My New DEC PDP-11/44 Project

I recently learned of a computer collector up in Santa Clara, CA who was moving to a new location, and who needed to get rid of a lot of his vintage computer equipment that he had in storage. He had already moved the good stuff that he was keeping, but he offered up piles of gear for free to anybody who would haul it away on some specific days. I didn’t want to drive up there myself at the time, but one of my friends at work suggested that one of his daughters and her boyfriend lived nearby in Tracy, and they might be willing to grab a truckload of equipment and bring it down south next time they drove back to visit him.

Everything all came together, and we met at a restaurant near my home on Saturday to transfer the loot. The haul consisted of four PDP-11/44 chassis and on ASR-33 teletype!

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Oct 272013
M4-GA-ROM-BC: TRS-80 Model 4 (Gate Array Version) ROM B/C EPROM Adapter

Fred Vecoven has designed a neat hard disk drive emulator for the TRS-80 model I, III, 4, 4P and 4D computers, called "FreHD". That is pronounced “Fred”; the "H" is silent. Ian Mavric manufactures and sells them, and I ordered one from him recently via his eBay store. It works quite well.

Now they’ve come up with a cool new innovation: Modified ROMs for those computers which allow them to boot directly from the FreHD without needing a floppy drive, and even present an on-screen menu to allow the operator to select which image to mount! Different ROMs are needed for each model and production variant of the 8-bit TRS-80 machines. My Model 4 happens to be the so-called “gate array” version. It uses a 24-pin mask-programmed 8k x 8 ROM which is not pin-compatible with common 28-pin 2764 EPROMs. It’s not too hard to adapt a 2764 with a few soldered wires, but I’m really allergic to blue wires. So, I’ve designed a little board which should plug in to the ROM socket in place of the original ROM, and then accept both the original ROM and a 2764 EPROM, with a jumper to select one or the other.

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Oct 222013
CoCoEPROMpak: A PCB for EPROMs in the TRS-80 Color Computer Cartridge Port

I designed this printed circuit board (PCB) to allow regular 2732 through 27256 EPROM chips to be plugged into the cartridge expansion port of a TRS-80 Color Computer. My main motivation was to crank out a simple design to try out a prototype PCB vendor called OSH Park. Unlike most small-run, online-ordered PCB vendors, they provide boards with ENIG (gold plating) surface finish, which is much better than HASL (solder plating) for edge connectors.

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