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Identifying proper DC wire colors...

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Lee Aufdemkampe

New Member
I am trying to rewire a gaming device. From the power brick there is a shielded white wire and the bare shielding. The device has a black wire and a red wire. Neither end has a plug attached so I will need to solder them together. I have a 50/50 chance of getting this right. If I get it wrong I destroy the device. How do I figure out which wire goes where? Thanks in advance for the help.
 

MaxHeadRoom78

Well-Known Member
Normal convention is Red is +ve conductor and black is -ve conductor.
Measure the voltage from the power supply end first.
Max.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
You measure which wire is positive and which is negative from the power supply - 'usually' screen would be negative and the inner core positive - but measuring with a voltmeter proves this 100%.

For the device, it would be nice to think that black is negative, and red is positive - but this isn't always the case. You could check to see if there's any obvious chassis connection in the device (such as the metalwork of a USB socket), this would 'usually' be connected to negative, but again it's not 100% guaranteed.
 

Lee Aufdemkampe

New Member
Thanks for the replies. I should mention that there is some sort of magnet (?) attached to the black wire on the gaming device. Is this useful to know?
 

MaxHeadRoom78

Well-Known Member
Can you post a pic?
Is it just a inductive device or is there any electronics at the gaming device end?
Can you give more details or a pic?
Max.
 

Les Jones

Well-Known Member
Most Helpful Member
You could try tracing the tracks on the PCB of the device near where the power wires are connected. there is a chance that there will be an electrolytic decoupling capacitor close to the power input to the board. If so then the polarity of the capacitor will be marked. There could be other clues such as the negative wire will show continuity to the negative power pin of any standard ICs. For example 74 series TTL, 4000 series cmos, 78xx series voltage regulators etc.

Les.
 

Lee Aufdemkampe

New Member
Hope this pic helps. The wires attach to a master circuit board which distributes to several other boards. I have two other identical boards so I was thinking that I could risk this one. But then I could ruin all the other boards attached to the master if I'm wrong. I wonder if I can isolate just the master board? I'll look into that.
 

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MaxHeadRoom78

Well-Known Member
That looks like a standard Wall-Wart cable, and the centre is Usually +ve, shield -ve. Which you can measure to confirm.
On the advice you have so far, see if you can determine if red is +ve!
Max.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
You can measure the wall wart. Easy enough. Center + and center negative both exist. center + is more common.

The polarity of the device may require some detective work. Red MAY be + and BLK may be -, but this is a guess.
Somethings that can help is negative usually goes to the the common traces. In other words, lots of stuff connects there.
Look for components with bands or polarity marks on the device connected to red or black. Post those pics.
A fuse can act as a safety net, but you may not have one handy and there's no guarantee that it will work.
 

Lee Aufdemkampe

New Member
Well, I finally just took a chance. The red & white wires were the proper connection. Of course, that means that the unshielded wire and black were also correct. The device was working but in the process of buttoning everything up I noticed that a different wire had broken. I soldered it back in place but when I tried to fire it up...Nothing! It seems I have solved one problem only to be faced with another. I'd go into details but they are beyond the scope of of the original problem. I only know to try trial-&-error as I am not a pro at these things. Thanks to all for your help!
 
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