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  #1  
Old 01-28-2009, 08:32 PM
philrrtx philrrtx is offline
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Default Museum restoration of 8800

I am starting the restoration of an Altair 8800 for the Goodwill Computer Museum in Austin. It was discovered about half-way through the Goodwill computer recycling process, and despite our best efforts, we were unable to locate some of the pieces.

In particular, it is missing the case and the dress front panel, which I am hoping I can purchase from Grant. I believe we can source the rest of the parts we need (switches, hardware, etc.) from other suppliers.

We have a Rev 0 original CPU board, four 4K dynamic memory boards (does anyone have schematics for that board?), and a 3P+S I/O board (I also need the schematic for this one).

The chassis is fully loaded with what appear to be factory-built bus cards. Interestingly, in a modification I haven't seen described anywhere, it has had a voltage regulator added to the output of the +8V A supply.
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  #2  
Old 01-28-2009, 08:49 PM
TomL_12953 TomL_12953 is offline
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Default Altair Board Schematics

Quote:
Originally Posted by philrrtx View Post
We have a Rev 0 original CPU board, four 4K dynamic memory boards (does anyone have schematics for that board?), and a 3P+S I/O board (I also need the schematic for this one).
All the schematics you need are in the manuals found at

http://vt100.net/mirror/harte/Altair/

Tom Lake
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  #3  
Old 01-31-2009, 04:07 AM
philrrtx philrrtx is offline
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Exclamation Schematics and switches

Quote:
Originally Posted by TomL_12953 View Post
All the schematics you need are in the manuals found at

http://vt100.net/mirror/harte/Altair/

Tom Lake
Thanks Tom. I found the schematic for the 4K dynamic memory board there. The 3P+S I/O board turns out to have been made by Processor Technology. So far I haven't found a schematic for it on line. Herb Johnson offers copies of the whole 84-page manual for 20 cents a page, but I hardly need 80 pages of "put this resistor in this hole" for a board that's already built. If anyone knows of an on-line source for this schematic, please let me know.

On a different topic, I'm having no luck at all locating the double spring-loaded switches used in the bottom row. The ST1-3 switch is still made by APEM (successor to American Switch, who made the originals) but none of their distributors currently has any in stock, and I'm not likely to convince any of them to make a special order for two pieces. If anyone knows of a source for that switch, or an alternate manufacturer's part number for same, please let me know.

We have four broken ones on the upper row and two on the lower row. The ST1-1s for data/address entry (upper row) are available from a couple of distributors, but none has the ST1-3.

Phil
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Old 01-31-2009, 06:42 AM
TomL_12953 TomL_12953 is offline
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Default 3p+s I/o

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Originally Posted by philrrtx View Post
Thanks Tom. I found the schematic for the 4K dynamic memory board there. The 3P+S I/O board turns out to have been made by Processor Technology. So far I haven't found a schematic for it on line. Herb Johnson offers copies of the whole 84-page manual for 20 cents a page, but I hardly need 80 pages of "put this resistor in this hole" for a board that's already built. If anyone knows of an on-line source for this schematic, please let me know.
Phil
Have you contacted the guy who wrote the manual, Mark Szpakowski?

szpak@eastlink.ca

He might have kept some of his old work.

Tom Lake
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  #5  
Old 01-31-2009, 01:16 PM
Geoff Harrison Geoff Harrison is offline
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Default

Quote:
Originally Posted by philrrtx View Post
The 3P+S I/O board turns out to have been made by Processor Technology. So far I haven't found a schematic for it on line.
Dave Dunfield has a copy on line. Click on the S100 link.

Geoff.
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  #6  
Old 02-02-2009, 12:13 AM
marty marty is offline
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Default switches

Grant, should be able to get the switches, either now or when He places his next order.. He should be able to add what ever you need on to a later order.
THANKS Marty
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  #7  
Old 02-05-2009, 05:00 AM
shunt1 shunt1 is offline
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Default

Today, I stumbled upon this forum and never realized that other "old farts" like me were still around. I was simply trying to show people what my first computer looked like.

I purchased my MITS Altair 8800 in 1975 and still remember a whining college kid that wrote BASIC for it...

Ok, this machine is absolutly useless, but how can I get one?

When I ordered my first one, MITS allowed me to purchase modules for $200.

Since I was in the Army and stationed in Germany at the time, my total income was only $400 per month. However, I was still able to build my first Altair 8800.

Today, after all these years, I am still doing the exact same thing. This machine changed my life forever.

How do I purchase one of these reproductions?
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  #8  
Old 02-10-2009, 05:01 AM
philrrtx philrrtx is offline
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Default A little progress

Got my replacement ST1-1 switches in and replaced the three broken ones in the upper row. I still haven't found anyone with the ST1-3s in stock, and APEM, the current manufacturer, was less than helpful.

So, in a "what have I got to lose" effort, I removed the ST1-3 with the broken-off handle from the lower row, and carefully pried the case apart. The guts looked good, just a broken handle. I then took one of the old ST1-1s that I had replaced, which only had a bent handle, and pried it open. I straightened the spring-loaded actuating pin from the old ST1-1 and used that handle to reassemble the ST1-3. Amazingly, it works. The little U-shaped case, which holds the mounting stud, isn't as tightly crimped on to the insulating block as it originally was, but it is quite functional. If I find a source for them, I'll replace it with a new one, but I can at least continue troubleshooting with my cobbled-together replacement.

The power supply survived its smoke test, and seems to be working OK, although I still need to check the ripple levels. The filter capacitor for the 16V supply looks like it has blown its safety plug, but it wasn't shorted, so I proceeded to apply power. A replacement is on order. Now, can anyone tell me why the front-panel power switch was oriented with down for ON and up for OFF? Seems backward to me.

In other news, the 4K dynamic memory boards I have turned out to be Rev 2, and all I've found for documentation so far has been for Rev 0. Of most interest at this point is how the little slide switches are arranged for address block assignments. Has anyone seen Rev 2 documentation?

Phil
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  #9  
Old 02-15-2009, 03:24 PM
marty marty is offline
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Talking 4 K dynamic memory bds

Hi Phil;
I would NOT recemend the 4K Dynamic Memory Boards, Maybe by Rev. 2 , they fixed the Problems, I would use Static memory boards, I had a 16K Dynamic Memory Board, when I had my 8800b, and it never worked, right or well. It would pass Altair memory tests, but it would not hold any thing for very long.... This was back when I bought it new in 1977, I don't have it any more... nor the Altair 8800b, I have one of Grants kits with Static memory, they work much better. Thank You Marty
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  #10  
Old 02-21-2009, 09:02 PM
philrrtx philrrtx is offline
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Default Progress report

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Originally Posted by marty View Post
Hi Phil;
I would NOT recemend the 4K Dynamic Memory Boards
Actually, I misspoke when I said they were the 4K dynamic boards. They are actually 4K synchronous boards, which I believe use static RAM chips. In any event, I finally figured out how the address switches work and it appears that all four are functional.

I have a front panel LED that is dead, but with the CPU and memory boards working, I'm hoping to be able to wrap this project up without too much difficulty.
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