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Chassis wiring
kerno Apr-16-00 01:18 PM
Is there a standard for chassis wiring in cases,
eg- what colors represent what voltage, which colors represent actives, which are grounds etc.
Any info greatly appreciated.

1. RE: Chassis wiring
lbyard Apr-16-00 05:34 PM
In response to message 0
Here’s a starter…

Disk Drive Power Connectors
Yellow +12 volts
Black (both wires) Ground
Red +5 volts

The color of front panel wires can be most anything, although some combinations are more popular among chassis manufactures than others (the plugs are usually labeled on recent, quality chasses). Likewise, there is some, not total commonality among the kinds of plugs used for the various wires; e.g., the speaker connector is almost always a four wire connector with the two speaker wires connected to the two outer positions (and they are usually red and black). Generally, if they are not labeled and you don’t have a diagram, you must physically trace the wires to see what switch, LED, etc. they are connected to and plug in the LEDs to determine which way they light. Plugging them in backwards will not hurt them. Plugging a switch into an LED header and closing the switch can damage the motherboard.

Motherboard power connectors generally conform to the drive power colors, but the best (and safest way) way to know which wire is which is to use the motherboard connector pin-out. -5 volts is usually, but not always white. With respect to Baby AT power supplies, the old saying, “Black in the middle you’re OK, red you dead,” applies to how the two motherboard connectors plug into the motherboard. The ATX power supply connector can only be plugged-in one way (or, at least that has been the case for all of the ATX power supplies and motherboards I’ve seen). The ATX specification suggests a color code, but states that no specific color code is required. Again, using the pin-out is the safest approach. Upgrading and Repairing PCs by Scott Mueller is good reference (I recommend it for all computer repair shops) and has the pin-outs for many types of power supplies. In summary, there is no color code standard. Larry

2. RE: Chassis wiring
kerno Apr-16-00 06:05 PM
In response to message 1
Many thanks Larry.

3. RE: Chassis wiring / front panel
diletante Apr-17-00 12:46 PM
In response to message 2
Tracing front panel wires is a pain in some cases (pun intended). A Volt-Ohm-Meter (VOM) is useful for determining what those pesky wires from the front panel are connected to. Most VOMs can be used to test diodes, including LEDs, in the Ohms (resistance testing) ranges, and the same measurement will detect a switch.

The computer should be off and unplugged. Test the wires while they are unconnected from the motherboard. Set the meter to an appropriate resistance scale for diode testing. Connect the test leads to the wire pair in question. Sometimes an extra set of hands is a big help. Look at the front panel for any lit LEDS. If one is lit, remove the test leads and it should go out. That pair of wires is identified. If no LED was lit, reverse the connection of the test leads on the pair of wires under test. (The meter is applying a small voltage to the wires, and it must be the right polarity for an LED to light up.) Look again for a lit LED.

If no LED lights up, keep the test leads connected to the wires and try the front panel switches. When you find one that changes the resistance from zero to infinity, you have found the right switch for that pair of wires.


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