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Altair 8800 Restoration Start-To-Finish w/Photos!

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
Last year I got lucky and came across an Altair 8800 (or what remained and was scattered of one) for sale in a nearby suburb. I did not know much about S-100 architecture at the time of purchase, but I knew the following: This computer did not have the original PSU, Bus, CPU, RAM or IO installed. It had a modified/custom PSU which was not output compatible with S-100. It had a custom bus which was not physical or signal-compatible with S-100. It had hand-wired and custom designed CPU and RAM cards for this bus. The front panel was quite modified and would not work with S-100.

Here was my luck, because despite all that, I was able to dig through the boxes from the estate and pull out the following:
Original PSU board
Original PSU transformers
Original MITS bus
Original MITS bus extender (never installed)
Original documentation

I also found the following cards in the boxes:

MITS 8800 CPU rev 0
MITS 4k Dynamic RAM (x2)
MITS 88-SIOA
TDL ZPU (modified)
TDL Z16 (modified)
TDL SMB (heavily modified - almost unusable)
GM Multi IO
A few 64k ram cards
Tarbell tape controller

What good fortune to have all of these parts!! I knew I had work ahead of me but had no idea how much. I can only attach 5 pictures per post so I'll start in and there will be many posts.

Here is my new purchase in the trunk ready to head home
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I am dying to see all of this stuff working again as it sits on my table, lifeless.
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Here's the original MITS bus w/CPU, RAM and IO cards still attached (as well as a mod to segue to the other custom bus)
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Original Manual in binder
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And many zines from the era (which are loaded with good info and none of them appear to be online right now so maybe I can start scanning at some point if anyone wants them)
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First look with the case off - look closely and you can see the mods to the front panel
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Modified MITS bus
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All this obviously needs to go.
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Removed the yuk-bus extension. Finally clean and ready for expansion.
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How lucky is this - the original wiring kit for the expansion!
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Getting ready to expand.
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The first few wires are soldered on
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Top view of the action
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The next 45 wires are added
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Now all signal wires are present - just need to add power.
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I was waiting for more edge connectors to arrive, so I went to start removing the old PSU. Why not leave it in you ask? Because it provided only Regulated 5v.... Not much good for S-100.
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Time to slip off the outer case
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Case coming off
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Interesting way it all goes together actually
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Here is the outer case and faceplate set off to the side while I do surgery.
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Front panel mounted still
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Removing old PSU
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Old PSU gone and desoldered all old bus wires from the front panel
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Case up on its side to start removing from the bottom
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Time to look at the manual to get an idea of how the rails need to be spaced to mount the original PSU and bus
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Old bus is finally out, time to move the rails
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Rails are adjusted to original spec
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Sizing up the PSU board and figuring out transformer arrangement
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3 original transformers all in a row
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Original PSU mounted up
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Here's a better shot of the original PSU board
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Hooray my Altair-spaced edge connectors arrived!
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First connector fits perfectly
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All edge connectors soldered in and continuity checked.
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Added power wiring and we are ready to install this 8-slot bus!
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So. many. solder. joints.
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PSU is totally installed now
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After checking voltages, PSU is reconnected to front panel for a quick test
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Front panel being removed for repair
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Front panel propped up for work.
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Many hours were spent tracing routes, patching, flipping LEDs, testing circuits, etc.
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This bus is dying to be connected to that panel.
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Original bus + expansion being attached to mostly repaired front panel
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Partial bus attachment
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Bus completely attached
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Bus and front panel placed back inside case and attached to PSU
IMG_20140225_145559.jpg

After replacing some capacitors on the Z16 and debugging one last missing connection for MWRITE, a successful test with a running adding program!
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Reinstalled the front panel and it's all going back together now so that it may now operate in its former glory.
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Wow the first person I met nuttier than me with their Altair... I did a similar tear down and rebuild on mine, though I found it easier to grab a roll of NOS white wire and just redo the bundles to the front panel to the motherboards. I also learned how to wire lace for mine as well from an old Bell Telephone guy at my hackerspace. The original owner did a beautiful job wire lacing the bundle into a harness, but the original wire on mine was too brittle it just kept breaking so it had to be addressed for reliability.

Great find on the connector kit wires, making those yourself is the biggest pain in the backside. I actually have another rev-0 motherboard to put in mine to bring me to 12 slots (I wouldn't go more than that with the stock PSU, actually that may even be too many), but I've been procrastinating almost a year because of cutting so many wires to perfect length.

Anyway... Great Job... don't forget to protect your front panel silk screen, from the pics on my phone here it looks like it's in good condition. If it is, try a couple of coats of polycrylic satin clear spray. It's water based so it won't interact with the powdercoat or the silkscreen. Before it hardens, you can wash it off and redo it if it doesn't come out well. I do suggest a few thin coats, then a last thicker coat. Mine actually has about 7 or 8 thin coats and a single thicker coat which was carefully wet sanded when hardened with 2000 then buffed (I have practice taking scratches out of exotic cars so this was't something I was concerned with, but you may want to skip that step).

Anyway protecting your font panel was something that was in one of the altair notes back then, and it's a great idea if you plan on toggling in more than just a simple address to a ROM.

Cheers,
Corey
 
Wow the first person I met nuttier than me with their Altair... I did a similar tear down and rebuild on mine, though I found it easier to grab a roll of NOS white wire and just redo the bundles to the front panel to the motherboards. I also learned how to wire lace for mine as well from an old Bell Telephone guy at my hackerspace. The original owner did a beautiful job wire lacing the bundle into a harness, but the original wire on mine was too brittle it just kept breaking so it had to be addressed for reliability.

Great find on the connector kit wires, making those yourself is the biggest pain in the backside. I actually have another rev-0 motherboard to put in mine to bring me to 12 slots (I wouldn't go more than that with the stock PSU, actually that may even be too many), but I've been procrastinating almost a year because of cutting so many wires to perfect length.

Anyway... Great Job... don't forget to protect your front panel silk screen, from the pics on my phone here it looks like it's in good condition. If it is, try a couple of coats of polycrylic satin clear spray. It's water based so it won't interact with the powdercoat or the silkscreen. Before it hardens, you can wash it off and redo it if it doesn't come out well. I do suggest a few thin coats, then a last thicker coat. Mine actually has about 7 or 8 thin coats and a single thicker coat which was carefully wet sanded when hardened with 2000 then buffed (I have practice taking scratches out of exotic cars so this was't something I was concerned with, but you may want to skip that step).

Anyway protecting your font panel was something that was in one of the altair notes back then, and it's a great idea if you plan on toggling in more than just a simple address to a ROM.

Cheers,
Corey

Thanks for the advice. I cleaned a bunch of ancient masking tape residue off of the front panel and was as gentle as I could be to get it off. It looks really nice and clean now but protecting will be a good thing as I do plan to use this machine somewhat and also want it to last in my collection for many years. There are a couple of small spots on my panel where the print has worn off but overall it's in really good shape and I'd like it to stay that way.

I don't know if I'm necessarily nuttier about the computer, but that there was just a ton of work to do to get it operational again. It was one of my big goals to actually restore this machine and having done it now, I can say that I'm way more confident about diving in with any piece of vintage hardware. I'm not skilled with wire lacing but I have a little of that left to do to make this clean on the inside so I'll just follow the pattern set by the former owner who did a pretty good.

I agree about the slot-count PSU limitation and think you should just hang on to that expander. I imagine if need 12 slots, it's so I can run maybe 8-10 cards (due to tight spacing - I can't put anything next to the Z16 I don't think), which would mean maybe I'd want 1-2 IO cards, Maybe a disk controller, CPU and 32-64KB of RAM and probably a PROM.. It's really pushing that power supply at that point I think, so a PSU upgrade would come first or at the same time IMO.

Do you have info on easy PSU upgrades from the day? I don't know anything beyond the basics about PSU design so I'd have a hard time just adding a big cap to the 8v line and hoping it could supply more when I know the transformer and diodes can only handle so much, but I've seen that mod in several machines.
 
Very nice job! I really like projects like these. You really are getting to know the machine
and all its ins and outs.

I would love to have such an machine too. But I guess it's impossible to find in the Netherlands...
So the only thing, with switches at the front, that I have is an Intel Intellec 8 MCS.

http://www.vintage-computer.com/vcforum/showthread.php?37488-Intel-Intellec-8-MCS

Regards, Roland
 
Hi All;
I Just saw this thread, and I am amazed at your work and labor of love..
Just wondering, Do you have any Idea of what the former owner had done/intended with all his mods.. Such as on the front panel, can you tell of his intent ??
There is a Transistor Mod for better output on the origional Power supply.. I have left the origional power supply in my machine, but disconnected it, and put newer Switchers that I got from Grant.. That way I can put it back to origional state if need be, but I now have cleaner voltages and protection in case of shorts or other problems..
I love the pictures !!!!

THANK YOU Marty
 
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