Paul
Thu Jun 19 21:11:54 PDT 2008
zalek wrote:
> On Jun 19, 10:57 pm, Paul <nos...@needed.com> wrote:
>> zalek wrote:
>>> Hello, I am trying to build a new PC. After connecting all the parts,
>>> I turned the switch on and... nothing.
>>> I suspect that the power supply is not working, or the circuit on the
>>> motherboard that switches the power supply on is not working.
>>> When I flip the switch on the back of the power supply on, the
>>> keyboard LED turns on for a second. However, when I press the major
>>> switch, nothing happens. No fans move, and there are no noises. I
>>> checked the major switch with an ohmmeter, and the switch seems like
>>> it works.
>>> I'm not sure if the power supply or the motherboard circuit that
>>> starts the power supply isn't working.
>>> So my question is, how can I check if the power supply is working?
>>> Thank you very much
>>> Zalek
>> There is a power supply spec here, so you can see the signal names.
>>
>>
http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2...
>>
>> To start with, the power supply is split into two pieces. The +5VSB
>> output, is available as soon as the rear switch is turned on. The +5VSB,
>> in turn, flows down the main power cable and powers some motherboard
>> logic.
>>
>> The second half of the power supply, operates the 3.3V/5V/12V/-12V
>> outputs. The power is "soft switched" by means of the logic level
>> on the PS_ON# signal. The PS_ON# signal normally is pulled to +5V,
>> by an internal resistor. To start the supply, PS_ON# needs to be
>> grounded (zero volt level).
>>
>> Inside the computer, the chain of command looks like this.
>>
>> Front Motherboard Grounds Main To main ATX
>> Power ------------ Logic runs ----- PS_ON# --------------- part of supply,
>> Switch on +5VSB to operate Cable fans start to spin
>> (momentary (latches when PS_ON# is
>> contact) signal) grounded
>>
>> An ATX supply can be operated on the test bench.
>>
>> 1) Connect a dummy load to the supply. You could use a couple old
>> hard drives, and connect them to the Molex connectors. I have
>> a home made load box that I use.
>>
>> 2) Switch on power supply at the back.
>>
>> 3) Connect Green to Black with a paper clip. The fans should spin.
>>
>> Then, you can use a multimeter to measure the voltages if you want.
>> I use a load box, drawing a light load (<100W), to help ensure
>> that the power supply will be regulating properly when I measure
>> it. I actually test new power supplies, before I use them.
>>
>> Paul
>
> Paul,
> Thanks very much for answering. I understood your explanation - now I
> know why the LED on the keyboard was turned on when I turned the back
> switch on.
>
> I'm not sure what you meant by "Connect Green to Black". I looked at
> all the cables coming from the power supply, and I didn't see anything
> green. Only yellow, red, white, black, blue, and purple.
> Thanks again, I really appreciate the help.
> -Zalek
If you check the formfactors.org PDF file, it has a pinout for the main
connector, with names and wire colors.
Pin Signal Color Pin Signal Color
--- ------ ----- --- ------ -----
1 +3.3VDC Orange 13 +3.3VDC Orange
[13] [+3.3 V default sense] [Brown]
2 +3.3VDC Orange 14 -12VDC Blue
3 COM Black 15 COM Black
4 +5VDC Red 16 PS_ON# Green <---
5 COM Black 17 COM Black
6 +5VDC Red 18 COM Black
7 COM Black 19 COM Black
8 PWR_OK Gray 20 Reserved N/C
9 +5VSB Purple 21 +5VDC Red
10 +12 V1DC Yellow 22 +5VDC Red
11 +12 V1DC Yellow 23 +5VDC Red
12 +3.3 VDC Orange 24 COM Black
HTH,
Paul