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k1atn
May 25th, 2018, 11:30 PM
Hello,

I am in need of some photos of the Altair 8800's power supply board as I can't seem to find any online. Specifically the bottom side. I have a few broken traces I need to fix, and the foil is completely gone on the board in a couple places. I don't want to bother with using the schematic to trace everything out at the moment due to a 40 hour work week taking up most of my time lately. LOL I just need to have a visual way to trace where the few missing foil traces go. I'm doing a complete rebuild of the board. Can anybody help me out with that?

-K1ATN

Chuck(G)
May 26th, 2018, 06:26 AM
Which power supply for the 8800? There were several.

k1atn
May 31st, 2018, 05:05 AM
The original 8800. Not the 8800a or B model, but the early one. My board says 8800 P/S REV. 0 at the top left corner. Also on the foil or bottom side it says MITS 8800 P/S Bd REV 0 in silver foil.

k1atn
May 31st, 2018, 05:47 AM
Also, is there any particular reason why the C14 Electrolytic has to be 500MFD? Is there some special logic to that, or can I just use a second 2200MFD like C13 which can be any value from 1000-2200MFD? I know staying within tolerance is a big deal, which is why I bought a 500MFD at 35v just in case, but those capacitors are there to filter out ripple, and create the right currents to the backplane and display board right?

Chuck(G)
May 31st, 2018, 01:26 PM
No reason at all--a 2200 uF cap at 35V should give you a little more headroom. After all, it's a linear unregulated supply. The point is to reduce the ripple to less than the headroom required for the on-board regulators. For the LM7805, the required headroom (by the datasheet) is 2V (i.e. you can have 1V of ripple on the +8V line and still be functional).

I've got the Rev 0 PSU in mine--I wish I didn't--it's so limp-wristed that it's a wonder than the thing worked at all. The PSU that I have in my Integrand box you could arc-weld with.

k1atn
May 31st, 2018, 06:19 PM
I understand that one. LOL Any chance You could snap a photo of the the foil side of it for me? I have more than a few traces that were completely torn off, and I want to make 100% sure that I'm reconnecting them where they should go.

Chuck(G)
May 31st, 2018, 09:44 PM
Oof, no offense, but I'd have to unearth the thing from other stuff and then disassemble it. I'm not willing to do that--perhaps there's another lister with one. Sorry.

It should be pretty simple to suss out from the schematic, though. It wasn't very complicated, IIRC.

smp
June 1st, 2018, 07:58 AM
Back in 2016, a member here posted that he'd built an Altair 8800 replica power supply board:

http://www.vcfed.org/forum/showthread.php?51123-Altair-8800-power-supply-photos

Maybe he can assist you?

Good luck!

smp

k1atn
June 5th, 2018, 04:47 AM
Thanks for the info guys, I'll keep it all in mind as I go.