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Altair 8800

Thanks Dave!! That actually makes sense to me!

This board's jumper area is pretty savaged.. I kind of wish I'd kept my other one. It's also missing a chip in the upper right socket. I think the manual says they need to be in pairs.

I do have a 4k DRAM board.. im tempted to try it despite the less than rave reviews..
 
So I decided for simplicity to configure the 1k board to the manuals expectation, which I think has memory starting at $0000. I then began entering data one byte at a time, and then reset and examined to make sure they were the same as entered. So far it seems to be holding the changes! Woo-hoo, a working Altair for $2000. Downright cheap hahaha

I'm hoping I have the input sequence right. The manual is a bit confusing, it says to enter things via D7 to D0. But then the table below with the sample program says D0 to D7

So I was interpreting 00 010 101 as:

Switch D7 - 0
Switch D6 - 0
Switch D5 - 0
Switch D4 - 1
Switch D3 - 0
Switch D2 - 1
Switch D1 - 0
Switch D0 - 1
 
Also new question - is there any way to restore the front panel silkscreening in the places where it's rubbed off without redoing the entire thing?
 

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Yeah I can't really tell if these are letraset originally or just paint on. It seems like where they've rubbed off there is a small see-through imprint, possibly plastic, where the marking was. That doesn't seem like a very efficient way for MITS to have done it though.
 
There are a number of things one can do the reduce the heat build up at the regulators. First check the voltage at the input to the regulator with a scope. You don't want it to drop below about 7.5 volts, on the lowest part of the cycle. Most of the regulators are rate down to 7 volts. You need to do this with a scope.
Measure the line voltage. as well.
Two solutions are to either use a variac to drop the line volt or use some old filament transformers to buck the line voltage. I use a variac but I did use some transformers for a piece of equipment that was rated for 240 volts on a 220 volt line. I just used them as boost auto transformers, in that case. Remember, such transformers can be small as it is the secondary current rating that counts.
Dwight
 
furball1985 said:
If it was me, convert to modern power supply with proper known good voltages and call it done. its inside the case nobody will see it, and you want to actually use the machine why deal with 45+ years of something else failing and blowing all the chips, works great for a week then you power it off for a while turn it back on and BOOM major damage.

if its a museum piece that is another story.
Click to expand...
I can strongly reccomend Meanwell's RSP-75-7.5 (7.5v) RS-25-15 (15v/-15v) power supplies for this sort of thing. Granted, both my S100 machines (A S100computers design and a 8800c) are thoroughly modern with per-board voltage regulation to match - I'm not sure how OG voltage regulators would handle voltages slightly below spec even after adjustment.
 
Hi all
I have seen following alter 8800 image for sale.
I am a bit puzzled since the front panel looks a bit different then other posted images.
It is missing the famout Altair 8800 logo but i guess this is just a name plate that was lost.
But also front marking is missing the dashed lines between a/d switches and leds.
It does have MITS SN 221335K
So i guess this was self assembled as a Kit.
Anyone can confirm this front panel?
Rgrds
LeorScreenshot_20230709_002244_eBay.jpg
 
Leorwn said:
Hi all
I have seen following alter 8800 image for sale.
I am a bit puzzled since the front panel looks a bit different then other posted images.
It is missing the famout Altair 8800 logo but i guess this is just a name plate that was lost.
But also front marking is missing the dashed lines between a/d switches and leds.
It does have MITS SN 221335K
So i guess this was self assembled as a Kit.
Anyone can confirm this front panel?
Rgrds
Leo
Click to expand...
Some discussion about it can also be found here:

The Altair shown in the photos you provided has been listed on eBay for a month now. It has been extensively modified and does not have any of the original boards except the front panel. It also does not have the original backplane and card guides, or power supply. The white front panel was likely home-made to replace a heavily worn original.
 
deramp5113 said:
I have a few reproduction name plates for the original Altair that look really close to the original if you want one.

Mike
Click to expand...
Hi Mike
I would like to purchase one such name plate for u if u still have spare ones.
Rgrds
Leor
 
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