15 Nov
2004
15 Nov
'04
6:53 a.m.
At 01:11 PM 11/15/04 -0500, you wrote:
I disagree. Testing a power supply is far from trivial and merely reading the open
circuit voltage tells you virtually nothing. Power supplies need to be tested under load
(like batteries) and things like ripple and regulation need to be checked. In fact, you
can damage many PSUs by not having a suffient load on them. And without a load others will
go into overvoltage and trip the crowbar circuits and thus appear to be bad. That's
why I said that you need the specs for the supplies so you can be sure of having an
adaquete load to prevent damage (or know if they can be operated with no load) and what
the permissible regulation and ripple specs are as well as the current capacity. If you
don't know exactly what they're supposed to do, how do you think you can test
them? AND as I pointed out, I've had tested powers supplies fail TWICE just in the
last week after operating a short time so even if you do an adaquete test you can't be
sure that they won't fail in use.
AND we haven't even talked about how you're supposed to know such simple things
as the rated voltage outputs and pinouts of odd-ball things like the Nord that was being
discussed. Tell me, do YOU know what the outputs of the Nord PSU are supposed to be and
where the test points are???
>>>> "Joe" == Joe R <rigdonj(a)cfl.rr.com> writes:
Joe> Testing power supplies before powering up a system is just plain
Joe> paranoid! (And I'm trying to be polite here!) There are a
Joe> thousand parts in modern computers that can cause just as much
Joe> damage!!!!!!!!
I disagree -- at least in the case of linear regulator supplies, which
is what you'll normally find in a classic computer.
A very simple and very nasty failure in a linear regulator is a short
in the pass transistor. If that happens, you get a much higher output
voltage, and there is no current limiting. It's a fair bet that this
will fry a large fraction of the semiconductors in your system.
If the supply has a "crowbar overvoltage protection" circuit in it,
that's a different matter. But testing a linear supply is trivial.
So why not do it?
If you let the magic smoke out of the computer, it's too late...
And you can still let the smoke out even after days of testing as I pointed out in my
message. And that's based on an ACTUAL example and not some hypothetical discussion.
Joe