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In need of some Altair 8800 power supply board photos

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k1atn

Experienced Member
Joined
Apr 28, 2013
Messages
106
Location
Albuquerque
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
 
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.
 
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?
 
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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.
 
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.
 
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.
 
Do you still need photos of the underside of the PSU board? I am actually finishing up restoring mines and took a few photos before I reassembled the components back onto it.

And regarding the 500uf capacitor - what is the voltage it should be rated for? I put in a 16v Sprague Atom 500uf, hope this will be okay. Actually, all the caps I have in there are 16v.
 
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