Derk said:
Hi,
I made a stupid mistake. I have an Asus M2A-VM-HDMI MoBo and I added a
SATAII HD to it. In the process, I ripped a few cables small off the MoBo.
These small cables are connected to the System panel connector accoring to
the manual.There's a double connector with 2 wires for the HDD led(yellow
and black wire) and 2 loose connectors (green and black wire)for the system
power led. Both are working, but I'm not sure I connected them the right
way:both should have a + and a - wire.
Question: how do I know what the + and what the - wires are?
TIA!
Derk
The PANEL header is usually defensively designed. That means to
some extent, you can't damage things with a wrong connection.
The LEDs on the computer case, are generally good for up to 5V PIV
(peak inverse volts). That means, for a cheap LED, you can reverse
the connections by accident, and all that happens is there is no
light. Once you rotate the connector 180 degrees and try again,
you'll get light. The LED is polarized in operation, but reversing
it is not the end of the world.
There are some high power LEDs (say 1 watt to 5 watts), which do seem
to be sensitive to reversal, so on a product like that, you have to
be extra careful to get it right. Some of those LEDs are used in
car headlights, or powerful personal flashlights. We don't usually
see that kind of LED in a computer (unless someone bought one
for the purpose of lighting up the inside of the case). If the LED
has a datasheet, you can check for a PIV rating, or read the text
discussing LED operation, for guidance on how careful you have to be.
In addition to LEDs, computers also have front panels switches, for
things like "Power" or "Reset". The switches are usually insulated
by plastic, so that the switch is "floating" with respect to the
chassis. The result is, you can rotate the switch contacts on the
associated PANEL header pair, without consequences. You can consider
the switches to not be polarized.
If you look at the various cables, there are also things like SPKR
wires, for the case speaker that does the "beep" at POST. A user
could plug those into the wrong pins. But if you look at the connection
pattern on the header, there usually isn't a way to get yourself in
trouble. The SPKR is potentially the most dangerous of all the PANEL
wiring, because sometimes designs have a raw connection to +5V. The
other side of the speaker lead, is "pulled down" by the driver, and
that is what makes the cone of the speaker move. One fault that
can have spectacular results, is if the +5V wire on SPKR is pinched
against the chassis, such that the insulation gets cut, and the wire
melts when a large current flows because of the short. If the
designers wanted, they could probably arrange that a little better.
In conclusion, you don't have too much to worry about. As long as
you locate the correct location for each wire pair, the interfaces
are relatively safe from reversal. And only the grossest ("I randomly
connect the wires") kind of usage, could result in a surprise.
You can even swap the RESET and POWER switches if you want. The current
flow through them is tiny - they use logic level signaling to achieve
their results. And if a LED was wired to the switch pins by accident,
there likely would be no long term effect, because the current flow
levels should be low. So the PANEL header isn't a thing that has
to be feared when you're working on it. Just do your best to get
as close as possible to the pins(s) each cable uses. If the LEDs
don't work, rotate them and the job should be finished. The switch
connections should not require rotation - just get the connector
on the correct set of pins.
Paul
