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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
903243_10151598253114104_1508154317_o.jpg

I am dying to see all of this stuff working again as it sits on my table, lifeless.
883705_10151598445434104_757699617_o.jpg

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)
459304_10151641688334104_683320878_o.jpg

Original Manual in binder
466946_10151641688184104_1881277252_o.jpg

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)
472736_10151641688264104_308229791_o.jpg
 

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
First look with the case off - look closely and you can see the mods to the front panel
479459_10151641688424104_169622165_o.jpg

Modified MITS bus
919913_10151663968514104_1703049450_o.jpg

All this obviously needs to go.
977386_10151663968639104_367165660_o.jpg

Removed the yuk-bus extension. Finally clean and ready for expansion.
462582_10151663968849104_680566503_o.jpg

How lucky is this - the original wiring kit for the expansion!
966621_10151666331094104_318072630_o.jpg
 

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
Getting ready to expand.
901276_10151666330644104_861521984_o.jpg

The first few wires are soldered on
919703_10151666330744104_321873596_o.jpg

Top view of the action
976754_10151666331294104_1322790930_o.jpg

The next 45 wires are added
324905_10151666331379104_681407125_o.jpg

Now all signal wires are present - just need to add power.
976095_10151670974064104_665447368_o.jpg
 

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
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.
977269_10151670974169104_651470777_o.jpg

Time to slip off the outer case
977905_10151670974364104_233766999_o.jpg

Case coming off
964475_10151670974459104_964348423_o.jpg

Interesting way it all goes together actually
966905_10151670974569104_2123131962_o.jpg

Here is the outer case and faceplate set off to the side while I do surgery.
967122_10151670974894104_228420769_o.jpg
 

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
Front panel mounted still
966257_10151670974724104_1994115944_o.jpg

Removing old PSU
919662_10151670975094104_129661821_o.jpg

Old PSU gone and desoldered all old bus wires from the front panel
978010_10151671359399104_1326167490_o.jpg

Case up on its side to start removing from the bottom
965036_10151671359619104_831714550_o.jpg

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
966758_10151671360199104_1361710875_o.jpg
 

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
Old bus is finally out, time to move the rails
977777_10151671360009104_763915410_o.jpg

Rails are adjusted to original spec
468027_10151675701659104_1435431079_o.jpg

Sizing up the PSU board and figuring out transformer arrangement
964225_10151675701484104_1716643563_o.jpg

3 original transformers all in a row
967272_10151675701829104_1080074689_o.jpg

Original PSU mounted up
966925_10151681195944104_683721466_o.jpg
 

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
Here's a better shot of the original PSU board
981571_10151681195774104_401993730_o.jpg

Hooray my Altair-spaced edge connectors arrived!
964004_10151705369284104_1044280020_o.jpg

First connector fits perfectly
980160_10151705369374104_1661261460_o.jpg

All edge connectors soldered in and continuity checked.
1008300_10151715773259104_118739672_o.jpg

Added power wiring and we are ready to install this 8-slot bus!
1015590_10151715773409104_1022908429_o.jpg
 

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
So. many. solder. joints.
981494_10151715773539104_474088991_o.jpg

PSU is totally installed now
965724_10151705369204104_1251466228_o.jpg

After checking voltages, PSU is reconnected to front panel for a quick test
965877_10151705369104104_1751996694_o.jpg

Front panel being removed for repair
1014509_10151715773639104_951061816_o.jpg

Front panel propped up for work.
1014517_10151715719679104_28709348_o.jpg
 
Last edited:

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
Many hours were spent tracing routes, patching, flipping LEDs, testing circuits, etc.
326899_10151718712474104_1820762394_o.jpg

This bus is dying to be connected to that panel.
977183_10151715773784104_1807530055_o.jpg

Original bus + expansion being attached to mostly repaired front panel
1015699_10151723933539104_182126544_o.jpg

Partial bus attachment
1025405_10151723933649104_752775028_o.jpg

Bus completely attached
1015671_10151723933734104_463615068_o.jpg
 
Last edited:

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
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!
1653676_10152276238284104_1501042826_n.jpg

Reinstalled the front panel and it's all going back together now so that it may now operate in its former glory.
IMG_20140225_135035.jpg
 
Last edited:

Corey986

Administrator
Joined
Dec 7, 2011
Messages
821
Location
East Coast USA
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
 

rbgrn

Experienced Member
Joined
Apr 5, 2013
Messages
66
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.
 

Roland Huisman

Veteran Member
Joined
Mar 24, 2011
Messages
1,315
Location
The Netherlands
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
 

Marty

Veteran Member
Joined
Jul 26, 2009
Messages
3,111
Location
Boulder , Colorado USA
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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