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Determining Motherboard Front
Panel Connectors
Last updated: 3/25/2003
Q. How can I determine where and how the various
front panel connectors (Power-on, hard disk LED, speaker, etc.) connect to
the header(s) on my motherboard without the motherboard documentation or
clear labeling?
A. You can plug LEDs in backwards and it won't
hurt them or the motherboard. Switches do not have a polarity and can be
plugged-in either way. The speaker can be plugged-in either way. It has two
wires that usually connect to a four-wire plug. You can plug a switch, which
is not closed (most aren’t except, possibly, the key lock on older cases),
into a LED connection on the motherboard and it won't hurt the motherboard
(or switch). Do not plug a LED into a switch header on a motherboard or a
closed (short) switch into a LED header on the motherboard. I generally start
with the Power on switch (ATX motherboard), and then the speaker, and follow
with the Power on LED. The Power on LED usually plugs into a five-pin header
or a group of five pins on a header with the keylock. Keep plugging it in
the four possible positions, backward and forwards, until it lights. The
key lock (if it isn’t on a five-pin plug with the Power on) goes into the
remaining two pins. You can do this with the computer on. Follow with the
reset switch and test. Next, hunt for the HD LED like the Power on, using
the Reset switch to boot the computer and light the LED… There are still
Turbo LEDs and Switches in the world and some motherboards still accommodate
a Turbo LED. I handle them last because the wiring is not consistent from
case to case and motherboard to motherboard, and they have no meaningful
function except eliminate the problem of having to explain to a customer
why the Turbo LED isn’t on and why the Turbo switch has no real purpose.
If I can’t get them to work after a few minutes or fidgeting, I leave them
disconnected and bundle them with the other wires with a zip (cable) tie.
Sometimes, one must resort to tracing wires to the appropriate LEDs and switches...
The last case LED I burned-out in my shop was about five years ago and that
was caused by error, not procedure. Larry
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