28 years in a hot attic....

[NavAir]

...and it still works!

In 1979, I purchased a Challenger 1P (while I was in medical school - I guess I needed a distraction). I really learned a lot about "modern" computers from that little device. I used a DEC PDP-8S in a High school computer class, and our college computer was an IBM that required one to create programs on punched cards to run! Although I don't have any formal electronics training, I built a number of Heathkits as a teenager, and come from a family of Electrical engineers...

I constructed a number of add-ons for the Challenger, including doubling the video resolution to 32x64 (and actually sold the instructions to do this for $8 each, making enough to pay for the computer - I'm in the First Book of Ohio Scientific by Clothier & Adams), interfacing a WWII formation control stick from a B24 to function as a joystick for games and a flight simulation program I wrote, and added a 610 memory expansion board. I also got an old IBM Selectric printer and interfaced it to be a printer/plotter. I wrote a patch for BASIC-in-ROM that added a "LPRINT" command to output to the printer. I even built a ROM burner and interfaced it to alter the monitor and BASIC ROM software.

The last time that I used it was in 1985 (I think). It went back in the factory carton and has been moved back and forth across the country at least 5 times, and has spent the last 28 years in my attic in TX (at temperatures of >120 degrees in the summer).

When I pulled it out, I wasn't optimistic that it would even power up. I bought an old Sony B&W monitor on eBay for video. I opened the Challenger case, and checked the power supplies, which were quite close to 5 volts, with no ripple. When I performed the "Smoke test", the darn thing actually booted to the "D/C/W/M" screen, but would not do anything else. Some quick checks disclosed that 37 years of disuse allowed some oxidation on the keyboard contacts, and after some cleaning, it actually booted up and I was able to write some short BASIC programs. Occasionally, it doesn't read all 24K of installed memory (probably oxidation on the memory chip pins), but I can live with that.

Now, I have to find the old cassettes with my programs on them and a cassette player (I think there may be one in the attic as well). Since I retired from clinical practice 5 years ago, I have had more time for old hobbies. Anyway, it was nice to find this site, and to know that I'm not the last man on earth with a functional Challenger 1P!

Some photos from the reanimation:

Back side of the 600 board, showing video display mods

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Memory expansion board

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Piggybacked 2114L memory chips for video expansion

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ROM chips with ZIF sockets for EPROM programmer

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Printer interface

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Back together in case

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[harrywalter99]

Great pictures. I am currently building up a C1P replica, so your photos are of particular interest. There is some wonderful blue wire art there.

With regards to the cassette player, I would recommend replacing the drive belt(s) early in the piece if you have problems reading the tapes, also a head clean will be kind to the tapes. I reloaded some data tapes after 40 years but I found that I only had success when I changed the drive belts on one of the 3 cassette players I had tried unsuccessfully earlier. It is very satisfying to load data after so many years.

[dave]

Welcome to the forum! Love the photos.

[NavAir]

Thanks! Doing a lot of aircraft maintenance (and other kinds of stuff) has gotten me into the habit of taking "closeout" photos whenever I have a piece of equipment open, just to verify something was done, or how I repaired something.

I did find my cassette recorder, and after replacing one of the belts and treating the pinch roller, that works fairly well.

Steve

[Scott Larson]

The 32x64 video expansion was the most complicated thing I had ever done in my young life. The instructions weren't very detailed and it involved cutting traces and soldering new chips on top of existing chips. It was effectively instructions on how to ruin your computer and initially that's what I had done. When I finished I got nothing but random characters on my screen and I knew I never should have tried anything like this.

But I didn't give up because I could tell it was sort of working. I just had to learn how CRTs work. I learned how the little beam drew stuff on the screen, how the bright dots were ones and the dark spots were zeros, how the bytes in video memory tell the character generator ROM which ones and zeros to send to the display, and how all those shift registers constantly scan through video memory throwing every byte at the video display over and over. Once I learned how all that worked, I figured out that I had soldered some wires to the wrong spots and that was putting the characters on the wrong spots on the screen. My destroyed computer worked again and worked even better than before with twice as many characters on the screen.

I felt great but I had no one to share this accomplishment with. None of my friends with Apple IIs and TRS-80s had any idea how their computers put stuff on their displays. When I tried to explain how I had modified my computer, their eyes just glazed over. Some thought I was crazy to tear up a working computer.

[dave]

The OSI video circuits are great playgrounds in which to learn digital design. I had a C2-4P with a 540 (no color) board, and I spent lots of time on the video.

[Scott Larson]

The TRS-80 and Apple II were also good for learning video. Video controller chips like the 6845 kept most of the mystery of how video works in the silicon.