Altair-what do I do first

From: J.C. Wren <jcwren_at_jcwren.com>
Date: Tue Sep 24 20:07:00 2002

        A less painful way may be to lift the output pin of the regulator from its
via. Or (and this is evil, but works, and is can be better than losing all
your unsocketted chips), cut the trace after output of the regulator. You
can always use a piece of foil tape or wire to effect a repair. This may
detract from the ultimate value of the board, but you're far less likely to
wreck it than removing irreplacable socketted chips.

        --John

-----Original Message-----
From: cctalk-admin_at_classiccmp.org [mailto:cctalk-admin_at_classiccmp.org]On
Behalf Of Tony Duell
Sent: Tuesday, September 24, 2002 20:24
To: cctalk_at_classiccmp.org
Subject: Re: Altair-what do I do first


>
> Good move -- don't plug it in yet.

_Neve_ plug in a classic computer without checking it first!

[Good advice on electrolytic caps deleted]

> In any case, detach everything from the power supply and check it out
first.
> Unfortunately, Altairs have no connectors for this, so you will have to
> desolder the wires.
> Some suggest powering it up slowly on a variable transformer, but I have
not
> tried that.
>
> After checking out the power supply voltages, unplug all of the cards and

The amin problem with S100 systems is that the PSU lines on the bus are
unregulated. The voltage regulators are on each card. And this means that
a defective regulator _on a card_ will wipe out all the chips on that
card, and may even put high voltages onto the bus lines and damage other
cards.

Therefore, do as suggested and get the unregulated PSU working first.
Then take the cards (one at a time) and remove all socketed ICs. Make a
diagram first, of course if you don't have the schematics/layout diagrams
for that card. You'd better hope that the expensive/rare ICs (CPU, ROMs,
RAM, LSI I/O chips) are socketed.

Then put the (essentially bare) card in the backplane and check the
outputs of the regulators on that card. Repeat for all the cards you
have. Put the ICs back into a card before starting on the next one
(unless you are a lot better organised than me!)

Then, and only then do you put populated cards into the backplane and
start testing logic functions.

-tony
Received on Tue Sep 24 2002 - 20:07:00 BST