Skybuck said:
Hello,
ASRock's motherboard 939A790GMH mentions the following in the quick
installation guide/manual:
Page 23:
System Panel Header:
O O O O
O O O O O - dummy
| |
GND RESET#
Antec 1200's reset switch connector has a brown and a white cable.
I have some question about this:
1. What is "RESET#" ? (I can understand "ground" but "RESET#" ???)
2. How does a reset switch work ? Does it "cut power" ? Does it make all the
electricity flow away via ground or something ?
3. How to connect the reset switch ? Should the brown wire go to GND or vice
versa ?
I also have a theory how the motherboard might get damage if it's not
grounded:
The gnd cables and/or the reset switch somehow makes it possible for the
chasis voltage and low ampere to briefly flow back into the motherboard,
this probably weakens the electronics, if this is done often enough
motherboard death would occur, therefore it would be best to ground the PC
so this can't happen ?!?
4. Last question, is this theory possible ?
Bye,
Skybuck.
Feel free to throw in any crazy theories you might have.
The RESET# and PWR# circuits should look similar to this. Neither circuit
carries heavy currents. The switches are momentary contact type, delivering
a pulse. It is up to the motherboard logic, to convert the pulse into
something useful. The signal coming from the circuit, is a logic level
signal. The "#" on the end, means they're active low, activated when
the signal level is in the low state.
You may have noticed, that under some conditions, there is a 4 second delay
from when you start pressing the front power button, until the computer
goes off. The motherboard has the ability to measure the duration of the
pulse, and to enforce a long duration requirement if the computer is up
and running. This is to avoid the computer switching off, if the power
switch is bumped for a short interval. The same delay is not applied,
when you try to turn on the computer in the morning - it starts immediately.
The motherboard logic takes care of all these tiny details. It
"conditions" the logic signal.
+5VSB Volts |
| +5V | -----+ +-----
| | | |
Resistor 0V | +----+
| ------------------ Time
+----------> Motherboard Input waveform
| Logic Active low logic
Push X Chip (Active Low)
Button->
Switch X
|
Ground
The body of the two switches on the front panel, is not connected to the
chassis. The body of each switches "floats" electrically. It's usually
insulated with plastic. A benefit of that, is it doesn't matter which
wire of the switch, goes to the "X" points in the circuit. You can rotate
the 1x2 connector either way and the circuit works. Either rotation
of the connector for the switch, works equally well.
*******
The LED outputs, such as the Hard Drive LED and the Power LED, use
a similar looking circuit. (I've removed the control element from
the picture here for simplicity.) The LED is "polarized" and only
lights when inserted one way. If you reverse the 1x2 LED connector,
the LED won't light up. If that happens, simply reverse it. The
LEDs used can take 5V PIV (peak inverse volts) and won't be harmed
by being connected in reverse. So if you cannot figure out how to
connect the two LEDs, you have a 50% chance of getting it right
on the first try, and if that fails, rotating the connector 180 degrees
will result in a working circuit.
+5V
|
|
Resistor
|
|
|
Power X <--- (+)
LED
X <--- (-)
|
Ground
*******
The motherboard may have a 1x4 position labeled SPKR, which connects to the
computer case speaker. Not all modern computer cases have a speaker, but many
do. The circuit driving the speaker, looks like this (this circuit is extracted
from the Intel reference schematic BXDPDG10).
+5V
|
X
SPKR
X
|
Resistor (~34 ohms)
|
Transistor
|
GND
A logic chip sends a repetitive square wave, at logic levels, to the
transistor. The transistor, in turn, turns the current on and off
to the speaker. The 34 ohm resistor (two 68 ohm resistors in parallel
in the Intel schematic) limits the current, and helps define how
loud the speaker will get. Generally, there is no volume control
for SPKR, as it is intended to just "beep".
The speaker is not polarized and placing the 1x4 in either orientation
will work.
One thing to notice in the above circuit, is one wire of the
speaker twisted pair, is connected directly to the power supply.
If the wire is pinched in the removable door of the computer, such
that the chassis grounds the wire, the wire will start to burn.
This is a silly "feature", and is about the only safety thing
to be aware of. When you route the SPKR wires inside your case,
make sure they don't get pinched inside the case. The wires should
be loose and the insulation in good condition.
The reason I know about this, is because a poster in one of
the groups, actually had the wire burn when it got pinched
and the plastic insulation on the wire was cut. When that happened,
I waited until I could look at some schematics, to see
what mistake had been made.
*******
The electronics on the motherboard are robust, even if you
don't believe it.
There are still some things about motherboards that are
mysterious, such as why is there so much trouble with
making a reliable PS_ON# signal (the signal on the main
cable of the power supply, that turns the supply on). That
too is a logic level signal, and seems to fail to work
properly, more than it should.
Paul
