JAIR 8080

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

JAIR 8080

Postby BillO » March 21st, 2021, 3:08 pm

One thing I will say about the JAIR is that this is definitely an intermediate build. Maybe I'm slowing down in my old age, but this took me about 8 hours to build up. Not only are there literally thousands of solder joints to make, but they are close together and the lands are generally very small making it difficult to make contact with the land and the pin with the iron at the same time. Even with my usual 1.5mm chisel tip. Not a beginner build.

That being said, it offers a heck of a lot on a single board.

Here is a shot of it mostly done. Only have some jumpers, connectors, LEDs and RAM to add after this.
IMGP9828s.jpg


Note the butterscotch brown chip to the left of the 8080. Its a Bulgarian 8224 clone. I could not find a reasonable source for a genuine Intel chip, so took my chances on this item and got a couple of them for $1.69 apiece.
IMGP9829s.jpg


I could not find the RAM chips at DigiKey, but found higher spec'd NEC D43256BCZ-70Ls on eBay that were supposed to be NOS and were only $2.99 each from a local supplier. However, this is what arrived.
IMGP9830s.jpg
IMGP9830s.jpg (28.35 KiB) Viewed 147 times

Not only were these NOT NOS, but it looks like they were pulled by an angry gorilla using his teeth.
Last edited by BillO on March 21st, 2021, 3:47 pm, edited 2 times in total.
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Re: JAIR 8080

Postby BillO » March 21st, 2021, 3:20 pm

Well, I cleaned up the RAM chips and straightened all the pins and will try them out at some point. I was a pretty sure this would not work first try. Not only does my clock chip look more like toffee than an electronic component, but the CPU is from China and the 8212s are from France and, well, thousands of solder joints...

I set it up in Altair CPU mode, plugged it in and ... it works!
IMGP9833s.jpg


I've still yet to test it in stand-alone mode. There could be all sorts of surprises there as that mode relies on a lot more components. However, before I do that I have to find myself an SD card under 1GB. That may prove to be more difficult than it first seems. I thought I has a 512MB one around here somewhere but it looks lie I tossed it some years ago. Anyway, if and when I find a little SD card I'll provide an update.
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Re: JAIR 8080

Postby AltairClone » March 21st, 2021, 8:28 pm

Wow, great progress! Thanks for sharing your work on this.

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Re: JAIR 8080

Postby BillO » March 26th, 2021, 6:56 am

Just as an update. It worked flawlessly for about 24hrs, then as I was editing a little BASIC program is just unceremoniously stopped. Tried resetting, then cycling the power. No joy. Once put into run mode it just seems to cycle through the addresses, almost like it can't see the data bus. The replica CPU still works fine. Anyway, It's going to be some time before I can trouble shoot this. I have other projects that need attention for a while.
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Re: JAIR 8080

Postby AltairClone » March 27th, 2021, 7:34 am

Well damn, that is frustrating. I love to get old equipment restored and working, but I must admit, once I’ve fixed it, I’m just annoyed when I have to fix it again. In this case it’s new hardware, so that’s doubly annoying :)

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