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Altair 680 vs b physical size change?

falter

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Dumb question.

In my covid induced state last week, I purchased an Altair 680 front panel. Neither the seller nor myself could tell if it was for a 680 or 680b.. it has no MITS markings on it. Anyway, I had assumed it wouldn't matter, I thought the 680 and 680b front panels were the same.. but lo and behold, it does not physically fit in my 680 case. Did they change dimensions at some point? Is the 680b case larger?
 

falter

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They appear to be about 0.25" larger than that all the way around. It's weird. They appear to be correct.. everything is in the right place, the PCB substrate looks vintage.. but the ICs are dated 1979. There are no MITS markings and no silkscreen. Very weird..
 

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deramp5113

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For the most part, the 680b was the first operational version of the computer. The original 680 never quite worked and the 680b replaced it just a few months after the original 680 was announced. The front panel board did not change dimensions between the 680 and 680b. You must have a “home-brew” version of the front panel.

Mike
 

falter

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Interesting. I didn't know people were home brewing Altair boards. I don't know how I find these things. It was kind of what I was planning to do myself anyway since finding an original board is really hard.

I may just salvage the switches and LEDs for my 8800. I don't know how easy it would be to only trim off a quarter inch around the board.
 

Chuck(G)

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Shouldn't be terribly difficult. I use a tile saw to trim raw PCB stock. An oscillating tool with the appropriate blade should be able to trim your boards. There appears to be plenty of excess stock around the perimeter.
 

falter

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Shouldn't be terribly difficult. I use a tile saw to trim raw PCB stock. An oscillating tool with the appropriate blade should be able to trim your boards. There appears to be plenty of excess stock around the perimeter.
I have tried both those things in the past and usually end up, even with guides and such, cutting away what I didn't want to. What I usually cut PCBs with is a score and snap tool, and then break the piece off. But because this is such a small amount to be removed, I'm not sure it would work. I suppose a laborious way might be to sand it down on the edges.

Very weird.. I wonder why they went larger than spec. I guess maybe they built their own chassis. I'm able to fit the switches in place into the holes in the front panel, so the PCB tracks etc seem to be scaled properly. It's just getting that extra material off safely.
 

falter

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While I'm on the topic - what I have right now is an original 680 case, this 'homebrew' switch panel, and an unbuilt Rev 0 680 motherboard. Apart from expandability and the usual gripes about building an unbuilt original board (which in this case I know at least three other examples exist of)... is there any compelling reason *not* to build a Rev 0 680? I know the b was more expandable.. but this is mostly going to be just for occasional tinkering.
 

Chuck(G)

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By "Rev 0" 680, do you mean one that duplicates (exactly) the function of a Rev 0 box--or do you mean one with an updated-to-b design? My recollection is that the original 680 suffered from design bugs.
 

Eudimorphodon

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But because this is such a small amount to be removed, I'm not sure it would work. I suppose a laborious way might be to sand it down on the edges.

If you have a reasonably steady hand I'd probably vote for a dremel with a cutting disk; clamp an improvised metal straightedge along the line you want to cut to keep from going in too far.
 

Chuck(G)

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Before I'd use sandpaper, I'd use a shoe rasp--much faster on FR4 stock or a coarse file. Of course, a belt sander with say, 80 grit paper would probably also make short work of the job.
 

alank2

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I'd also wear some breathing protection as you don't want to be breathing any of that FR4 in.
 

Chuck(G)

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Yes! that goes without saying. That glass dust can be be pretty nasty if inhaled. However, masks seem to be pretty easy to come by, for some reason... :)
 

falter

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By "Rev 0" 680, do you mean one that duplicates (exactly) the function of a Rev 0 box--or do you mean one with an updated-to-b design? My recollection is that the original 680 suffered from design bugs.
Well, what I have is a motherboard marked 'Rev 0' by MITS. It was a totally unbuilt unit (probably for the reason you described) that was framed. The frame did not survive. I already had the 680 case, which I now assume would be applicable to the Rev 0 or B.

So my desire here is just to use what I have - I don't have a 680b board to build from. Assuming I could get this Rev 0 board to work, I'm not sure what I'd be missing from the b other than expandability.
 

deramp5113

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The rev 0 board did not have the 6850 ACIA, so console I/O was bit-banged. I haven’t seen a listing of the monitor for the rev 0 board, but I imagine it would be similar to the standard ASCII monitor but using the single bit I/O port logic as used in the Model 15 Teletype (Baudot) monitor (also shown in the 680b manual). The original plan at product announcement was to have a fully functional front panel like the 8800, but in the end, all they could really do with the front panel was examine and change memory. You will have to have a monitor PROM no matter what.

Mike
 

BobApplegate

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Does anyone know of an accurate mechanical design of the motherboard? Dimensions hole locations, etc? It looked like a compact board that fit a rather compact chassis.

Bob
 

falter

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Does anyone know of an accurate mechanical design of the motherboard? Dimensions hole locations, etc? It looked like a compact board that fit a rather compact chassis.

Bob
I had thought of scanning my unbuilt board... but I nearly lost some Mark 8 boards in transit and got too spooked. I think the 680 Rev 0 and b boards are different too.. I could provide the exterior dimensions. It doesn't fit on my scanner unfortunately so getting an accurate measurement for holes etc would be tricky.
 

BobApplegate

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Any dimensions would be appreciated. I have bits of information from other places and might be able to piece it together. Ideally I'd like a b motherboard dimensions.

Thanks!
Bob
 
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Any dimensions would be appreciated. I have bits of information from other places and might be able to piece it together. Ideally I'd like a b motherboard dimensions.

Thanks!
Bob
Bob,
I’ll be starting some restoration and cleaning of my 680b that will involve removing the MB from the case. I’m happy to forward dimensions to you. Do you need case dimensions as well as the MB and front panel?

Stan
 

BobApplegate

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Any/all board dimensions would be appreciated! I'm sure there are others who would like this information too! There are a lot of other vintage systems that were made in large numbers so finding boards in other people's collections or an eBay are fairly easy, but the 680b is hard to find. There is a lack of information about them so anything you can provide would be much appreciated!

Bob
 
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