Altair-what do I do first

From: Peter C. Wallace <pcw_at_mesanet.com>
Date: Wed Sep 25 13:39:00 2002

On Wed, 25 Sep 2002, Tony Duell wrote:

> >
> > 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
>
> A word of warning if you try this. Some (only a few, but) 3-terminal
> regulators are unstable if don't properly decouple them. So if you
> totally disconnect the output pin, add a 100nF capacitor between the
> disconnected pin and the ground rail.
>
> It may be impossible to do this, BTW, if the regulator is a TO3 (metal
> can) one _and_ the power distribution is on an internal power plane of a
> multi-layer PCB. Multi-layer PCBs are not common in S100 machines, but
> they did exist at that time.
>
> > can always use a piece of foil tape or wire to effect a repair. This may
>
> Indeed. Don't just bridge the trace with a blob of solder, though. It
> will give problems later.... In fact _always_ solder a wire across a
> track break or cut rather than just using a blob of solder.
>
> > detract from the ultimate value of the board, but you're far less likely to
> > wreck it than removing irreplacable socketted chips.
>
> I've never damaged a chip removing it from a socket. But desoldering
> irreplacable chips (i.e. removing unsocketed ones) is something I'd not
> want to do too often.
>
> It depends on the board. If you can pull almost all the ICs, perhaps just
> leving a bit of TTL, then try it like that. TTL is still fairly easy to
> get. If, on the other hand you've got soldered-in RAMs, or LSI parts,
> or... then disconnect the regulator from the rest of the board rather
> then trying to remove the ICs.
>
> -tony
>
>


Seems like an easier thing to do would be to use a lab supply to power the
unreg, ramp it up slowly, and make sure the regulators are working.

Better still, if you are testing the cards one at a time with an external
supply, tack on a 5V (set to 5.5 or so) crowbar on the output side of the
local 5V regulator -- no cut traces, only tacking on 2 wires temporarily...



Peter Wallace
Received on Wed Sep 25 2002 - 13:39:00 BST