IMSAI 8080: Do you want to play a game ?

[fdiskitup]

I saw this in a box of modems and agp cards, is it what I think it is ? (IMSAI 8080, S-100 cpu/mpu).




Seems to be missing CPU and some other chips, and there is some rough soldering arround the power ic.
Cost me $1 + tax.

 

[twolazy]

Indeed it is!

 

[fdiskitup]

I guess somebody upgraded their IMSAI to a Z80 or 8085 cpu card.

 

[fdiskitup]

I think this will go nicely with the cpu card … looks like it needs the active termination finishing, about a hundred resistors needed along the front.

 

[hmb]

I think this will go nicely with the cpu card … looks like it needs the active termination finishing, about a hundred resistors needed along the front.

This is a Vector 8803 backplane, which has an active termination circuit. In addition to almost 100 resistors, the circuitry also uses several active components.
Vector licensed the design from Godbout/CompuPro - you can find the schematic, parts list, and assembly manual starting at page 209 of this manual:

https://deramp.com/downloads/mfe_archive/010-S100%20Computers%20and%20Boards/00-CompuPro-Godbout-Viasyn/10-CompuPro%20S100%20Boards/CompuPro%20User%20Manuals%201975%201980.pdf

IC2 is a 4250 op-amp, now long obsolete and hard to find. Anchor Electronics still has them in stock. You might as well also replace the ancient axial tantalum caps that were installed on the board.

Although the terminals on this board are labelled +5V and +/-12v, in a typical S100 system these terminals would be connected to a source of unregulated +8 VDC and +/-16VDC.

 

[fdiskitup]

100 resistors, the circuitry also uses several active components.
Vector licensed the design from Godbout/CompuPro - you can find the schematic, parts list, and assembly manual starting at page 209 of this manual:

Thankyou for the link. There is some gold in there about memory cards and interface serial ports.

I couldnt resist this imsai 16k memory card on ebay, it also needs some chips and some care …. You can probably guess where this is going …. Cpu, memory, backplane… did the 8080 machines use serial or parallel to communicate with a terminal?
I think the switches and lights frontpannel might be an imposibility to find, but it should be possible to put in an eprom and get it to boot that way.

 

[daver2]

It is interesting that someone put A1, A2 and A3 in sockets but soldered the rest in. Unless they were trying to repair the board and gave up after replacing A1, A2 and A3 - so took the CPU out of a dead board?

Dave

 

[hmb]

Thankyou for the link. There is some gold in there about memory cards and interface serial ports.

I couldnt resist this imsai 16k memory card on ebay, it also needs some chips and some care …. You can probably guess where this is going …. Cpu, memory, backplane… did the 8080 machines use serial or parallel to communicate with a terminal?
I think the switches and lights frontpannel might be an imposibility to find, but it should be possible to put in an eprom and get it to boot that way.

I would not have recommended you buy that IMSAI 16K RAM board - that board is a "project" mostly of interest to someone trying to restore an original IMSAI rather than something you can get up and running right away. This board has already been cannibalized for some of its ICs - not a good sign. The cheap TI edge-wipe IC sockets are a problem. There is a CompuPro RAM17 64K S100 RAM board currently on eBay that would have been a far better choice.

Before buying more boards, I suggest you first thoroughly consider what the end result of this project is going to be. An S100 system with 16K of RAM, a serial interface board, and a small software monitor program running from a ROM is going to cost you several hundred dollars to get running - and you will not be able to do much with it. To get a minimal S100 system up and running based on what you already have, you will also need:
- a board you can plug an EPROM into with monitor ROM software. Unless you have a front panel or a board that provides a power-on jump circuit, the monitor ROM you choose will need to have a starting address at 0000h (the reset address of the 8080)
- a serial interface board that the ROM monitor software has been designed to work with. You can use any PC running serial terminal emulator software as your S100 system's console.
- of course, a power supply for your backplane. Highly recommended you use three inexpensive switching power supplies, one to supply +8V and two to supply the positive and negative 16V.


A "switches and lights" front panel is not impossible to find however you either (a) need to build one, and there are several DIY designs available to choose from or (b) you need to buy an original IMSAI - expensive, but virtually always available for sale on eBay.

Consider joining the Google Groups S100 discussion group - more S100 help available there than anywhere else. Also, look at this web site for a lot of information on S100 systems, and projects for those who want to build a new S100 system rather than using old parts salvaged from vintage systems:

S100 Computers

S100 Computers Home Page

www.s100computers.com

 

[fdiskitup]

This might be quite a long term project, but it keeps me out of the pub.

Ive got a couple of SS-50c machines working with serial links, this has been great fun.

I’m right at the beginning of the S100 learning. Maybe the ultimate goal is to get a monitor and minibasic up and going… perhaps a cassette data recorder. I dont think I need 64k of dram

I tend to look for cheap stuff that needs work, missing chips, bad tantalum caps, blown rifa caps, battery damaged traces, gold scrap, etc.. I’m hooked on that moment when you power something on for the first time and it actually works.

 

[hmb]

This might be quite a long term project, but it keeps me out of the pub.

Ive got a couple of SS-50c machines working with serial links, this has been great fun.

I’m right at the beginning of the S100 learning. Maybe the ultimate goal is to get a monitor and minibasic up and going… perhaps a cassette data recorder. I dont think I need 64k of dram

I tend to look for cheap stuff that needs work, missing chips, bad tantalum caps, blown rifa caps, battery damaged traces, gold scrap, etc.. I’m hooked on that moment when you power something on for the first time and it actually works.

You could consider getting a 2SIOJP board:

2SIOJP

88-2SIOJP Enhanced Serial Interface Board

deramp.com

That board, along with the boards you already have, would allow you to get up and running right away with either its included monitor or MITS extended ROM BASIC (as originally used on the Altair).

 

[fdiskitup]

And dont think that this isnt like catnip for me .. $900. I’d have to sell a kidney.

 

[fdiskitup]

You could consider getting a 2SIOJP board

Thats perfect for this project, eprom and serial ! Thanks for pointing it out.

 

[DDS]

"IMSAI 8080: Do you want to play a game ?"​

I liked the "WarGames" reference.

The WarGames IMSAI – The Official IMSAI Home Page

www.imsai.net

"A STRANGE GAME.
THE ONLY WINNING MOVE
IS NOT TO PLAY.

HOW ABOUT A NICE GAME OF CHESS?"

 

[fdiskitup]

for future S100 Wannabees like me:- the JAIR (Joint Altair(Joshs') IMSAI Board) board gets you a fully working single board S100 computer to get started with.
Now to test that IMSAI CPU board that started this thread...

 

[wperko]

for future S100 Wannabees like me:- the JAIR (Joint Altair(Joshs') IMSAI Board) board gets you a fully working single board S100 computer to get started with.
Now to test that IMSAI CPU board that started this thread...

View attachment 1265759

Hi,

Not much different than my Test Bench Computer setup. I too have a J.A.I.R. SBC with an IMSAI mini-Front Panel.

I've been collecting boards to build the reproduction IMSAI cabinet into an IMSAI-ZPU computer so when I finish a few other projects I'm working on (like the reproduction SciTronics RTC S-100 board) then I'll move the IMSAI mini-Front Panel and J.A.I.R. to the Test Bench setup.


.

 

[fdiskitup]

very nice - I like the upcycling of a Walmart box !

do you see any issue with the 3 power supply's starting up simultaneously - I'm guessing they don't all stabilize at the same time ? would it be a bad thing to feed +15V/12V to the CPU before there is +7.5/5V ?

 

[wperko]

very nice - I like the upcycling of a Walmart box !

do you see any issue with the 3 power supply's starting up simultaneously - I'm guessing they don't all stabilize at the same time ? would it be a bad thing to feed +15V/12V to the CPU before there is +7.5/5V ?

Hi,

Using the three Mean-Wells is pretty standard for S-100 buss computers now days.

I have them on three computers; Altair 8800c, IMSAI-JAIR and the Test Bench Computer ... no problems.


https://www.brainless.org/Altair/


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