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IMSAI reassembled

cchaven

Experienced Member
Joined
Jul 31, 2003
Messages
169
Location
Roanoke, VA
Some of you may have seen a bare bones (chassis, cover, PSU, backplane and front panel only) IMSAI 8080 on everyone's favorite auction site a few months ago. It was missing all but 4 of the switch paddles, as well as all of the S-100 bus cards. I'd always wanted one, but always balked at the prices being asked, but since I tend to like basket cases that I have to do tons of research on in order to repair, I picked this one up. I was able to get a new switch escutcheon from Todd Fischer after a bit of waiting and I repopulated it with S-100 cards I already had plus a few that I picked up for the project. The switch paddles I ordered from a gentleman in Austria as a complete set.

It's now complete! Is it cosmetically perfect? no, as it has some scratches and scuffs. Is it functional yet? no. But it's complete and two of the cards I was able to figure out that it had installed prior, and that it now has again, are the IMSAI SIO-2 serial board and the Tarbell cassette board. Both of these are hard wired to the back panel. The original builder also put the power switch and fuse on the back panel, as there's no sign that either have ever been wired to the normal spots on the PSU board.

To be funcitonal, I first need to go thru and check all of the addresses between the memory boards and then come up with a simple monitor that I could put into a 2708 EPROM that uses the IMSAI SIO-2 board for terminal IO. Currently, I have the following boards installed:

Solid State Music CB1 8080 cpu board, wired to the front panel
Vector 12k PROM/RAM board
Processor Tech 4KRA RAM board
TDL Z16 16k RAM board
SD Systems Versafloppy I floppy controller
IMSAI SIO-2 serial board
PMMI MM-103 modem
Tarbell cassette interface board

Currently, it's sitting out on display, sitting on top of a generic 8" floppy enclosure that holds 2 Siemens FDD 200-8 floppy drives. For the moment, I'm just happy to have it complete..it is a striking looking system. Hopefully at one point though I'll be able to finish getting it up and running.

Jeff
 

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Good luck. I have one as well. These projects can take many months. Take your time as to avoid mistakes.
 
Hi,

Nice job, for sure!

I also have an IMSAI 8080 that I play around with off and on. I, too am missing some of the toggle switch paddles. I got some replacements from a fine Seller over on eBay, but I have struggled to install them. Do you have any suggestions, or procedures that you used to get this done without damaging anything? Is it actually possible to do without bending the metal ears out so that the paddle is too loose? Do you have to disassemble the entire Front Panel in order to do it?

Right now, except for the few missing paddles, my IMSAI is working perfectly (as perfectly as that design and technology will allow). I am hesitant to tear into it for fear of damaging things and making even more work for myself.

Any advice you may have would be appreciated.

smp
 
Hi smp,

I read the instructions that Todd posted on IMSAI.NET for removing and insalling the switch paddles, but it didn't seem to work for me..and I was trying to use a minature screwdriver to get between the paddle and the metal ear. I finally ended up angling the paddle and pushing on it just enough to get the other side to pop in. Some of the paddles aren't in there the tightest now..but since I didn't have to remove them, I don't know if it's from the way they were removed before, or if I bent the mounting ears installing them.

Aren't you the one that modified the IMSAI SCS code to use with yours? I see that the source on Todd's site suggests that it is used with the SIO-2 board. Did you put it in ROM?

Take care
Jeff
 
Hi,
I also have an IMSAI 8080 that I play around with off and on. I, too am missing some of the toggle switch paddles. I got some replacements from a fine Seller over on eBay, but I have struggled to install them. Do you have any suggestions, or procedures that you used to get this done without damaging anything? Is it actually possible to do without bending the metal ears out so that the paddle is too loose? Do you have to disassemble the entire Front Panel in order to do it?
smp
I'm assuming you have some broken switch paddles. You will need to completely remove the plexiglass covering the front panel with an (allen/torque?) wrench. Watch out to keep the IMSAI graphic photograph clean and free of scratches by using a towel to place this on. You then unscrew the front panel circuit board and detach the front panel. The paddle switch assembly can be unsoldered and replaced. I purchased my replacements from Fischer F. company. I did not bend the metal ears, because I replaced the entire plastic / switch assembly by soldering the old one and removing it and then soldering back in the new one.
 
Hi smp,

Aren't you the one that modified the IMSAI SCS code to use with yours? I see that the source on Todd's site suggests that it is used with the SIO-2 board. Did you put it in ROM?


Hi Jeff,

Thanks for your take on the switch paddle replacement. I'm glad to hear that I am not the only one who cannot make use of Todd's directions. ;)

Yes, I used the source code for the IMSAI SCS as the basis for my first monitor program. I stripped out all the code associated with the editor and assembler, as well as the serial I/O, because I am using the SIO board from the s100computers.com web site. John Monahan has posted a bunch of sample code there to support the boards they have designed, so I used his sample code for the serial I/O portion. The remaining code fit easily within a 2K EPROM.

I went on and found some more code to read Intel Hex format files so I could assemble programs outside of the IMSAI, and then read in the hex file from the external assembler. That code had a lot of redundant code in it for ASCII-to-binary conversion, and I struggled with trying to integrate the two pieces of code together, because the redundant code became too big for one EPROM.

Eventually, I dumped that code in favor of a modified TDL monitor that is available for the Z80 processor, plus that additional code to read Intel Hex files. Of course, I had to switch over from the IMSAI processor to a Compupro Z80 processor board, but that change also bumped me up from 2MHz to 4 MHz operation.

Anyway, that's all I have running at present: the Compupro Z80 CPU, a Compupro 64K RAM board, and the Serial I/O board from s100computers web site. It is solid and stable. One of these days, I will get to building up a couple of more boards that I have acquired from the s100computers web site, but that is being saved for later right now.

smp
 
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Thanks for the encouragement everyone! SMP, would it be possible to take a look at your modified SCS? I also have a Z80 board I could put in the IMSAI...a Northstar board with the front panel connection...the manual outlines the modifications needed to it to use it in the IMSAI. If I put together a monitor I could put in one or more 2708's, then I could use the Vector PROM/RAM board with either CPU board. I also have a total homebrew S-100 bus machine that has a Z80 SBC with it's own custom monitor....since it's a SBC I may pop it into the IMSAI after slowly bringing up the PSU and checking things out. I'm definately taking things slow though..but it's all very exciting.

Jeff
 
Where the heck do you even get S100 boards anymore? Any places I know of dried up almost ten years ago as gold/copper prices began their rise to present day prices.
 
SMP, would it be possible to take a look at your modified SCS? I also have a Z80 board I could put in the IMSAI...


Hi Jeff,

I would be glad to share my source files with you. I can send you both the modified IMSAI SCS code for the 8080, and the modified TDL code for the Z80. Send me a PM with your e-mail address and I will send you those files tonight after work.

I can even give you a pointer to a fellow up in Canada who can take your Intel Hex file and put it into any size EPROM you want for very inexpensive prices. I have had him do a 2716 EPROM for me three different times throughout the past 12 months, and he only charges $10 each time. That's for everything: the EPROM, burning the code, and sending it back to me. For someone like me who will only need this kind of help once in a great while, he is the greatest.

smp
 
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Where the heck do you even get S100 boards anymore? Any places I know of dried up almost ten years ago as gold/copper prices began their rise to present day prices.

www.s100computers.com is a great place to purchase newly designed S-100 boards that work great and have capabilities ranging from what was available in the late 1970s to much more modern processors like 8088, 80286, 80386 (coming soon), as well as modern memory, video output, and CF card storage.

smp

EDIT: If you are looking for something specific, you can always post in the Vintage Computer Items Wanted forum here. There are plenty of folks who have stuff that they can be coaxed into parting with - especially to someone here on the forum who cares. ;)
 
Where the heck do you even get S100 boards anymore? Any places I know of dried up almost ten years ago as gold/copper prices began their rise to present day prices.

My company was one of the last Compupro System Centers before they closed down. While I have not always been actively advertising, I've been selling and servicing Compupro S-100 Systems, boards, and software continuously since 1980. I don't have as large an inventory as I did in the mid-1980s to early 1990s (I carried as many as 300-400 S-100 boards at a time, but still have over 100 new and used Compupro S-100 boards, system enclosures and disk drive enclosures, in stock. Yes, I still have some brand new from the factory S-100 boards in stock, along with dozens of used S-100 boards, some bare S-100 boards, and original Compupro technical manuals. I have some new and used 5.25" and 8" floppy drives available for sale, and I still service floppy drives.

Most all hardware that I sell includes a six month warranty (unless modified). If you need anything Compupro, email me or phone 909-820-9850.
 
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