25 Sep
2002
25 Sep
'02
6:39 a.m.
On Wed, 25 Sep 2002, Tony Duell wrote:
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
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