# No boot - Testing Power Supply with Mulitimeter



## Watchworks (Oct 4, 2009)

My symptoms: PC running when I left the house, and off when I returned. Power button does absolutely nothing, PSU fan does not move, a small green light on the back of the PSU is on. So I am trying to diagnose bad PSU, bad Power On Button, or bad motherboard.

Thanks for the posting at http://www.techsupportforum.com/f210/test-your-power-supply-with-a-multi-meter-151526.html#post829293 that provides instructions on testing power supply voltages.

After disconnecting the PSU connectors to the components (DVD writer and the system's only hard drive), I got the following measurements that are shown in brackets, [] in front of the instructions from the link above:

[Measured 2.66 volts]


> 1. Check Pin 9 (Purple, VSB) is about 5V. This is the standby voltage and is always on when the power supply is live to an AC source. If not 5V then problem with PSU, or a possible short circuit in motherboard or a peripheral device has caused the PSU to auto-shutdown.


[Measured 2.34 volts]


> 2. Check Pin 14 (Green, PS_On) should be about 3~5V. If PS_On is zero Volts and VSB okay then disconnect the pc case Power On switch to see if voltage comes up, if so then bad switch.
> [No change, stays 2.34 volts] 3. Press the pc case Power On switch and PS_On should drop to ~0V.
> If no change, the suspects are faulty switch or CPU. If the motherboards PS_On pins are accessible by removing the pc case's power on leads then short the 2 pins with a light tap from a screwdriver tip to trigger the power on. Another way is to use a jumper wire to short PS_On to GND. If no change in PS_On then probable fault is CPU.


It seems to me that since the standby voltage (Pin 9 Purple, VSB) and power on voltage (Pin 14 Green, PS_On) are lower than the 3~5 volts expected range, this problem would be the power supply of this 5 year old PC, however the quotes above imply there could be other problems, and I don't have the extra funds right now to guess at it by buying a PSU that I may not need.

I also followed the steps found on other sites to short the power on voltage (Pin 14 Green, PS_On) with a black GND by disconnecting the 24-pin ATX connector from the mother board, and using a paper clip to connect these two wires in the connector. The PSU fan then works, and if I reconnect the DVD player, its open/close door works. Re-applying the short and measuring the voltage for the DVD player power connector (multimeter Red lead in Yellow wire; Black lead in black wire) shows 11.76 volts almost immediately, and stays steady; according to that other site, 10-15 volts is expected, explaining how the DVD player works.

What's the next step? :wave:

Can I test the power switch? The instructions provided above weren't clear to me -- do I disconnect the power switch connector from the mother board and connect two of the 9 pins now revealed on the mother board, and without a schematic, which ones? FYI - the connector has 5 potential connectors on the top row (blank, blank, blank, Black, Yellow) and 4 on the bottom row (Black, Red, Black, Blue).

I have an HP Pavilion a1050y computer, Pentium 4

Power Supply Unit (PSU) is HIPRO HP-03057F3R
500 MB RAM
[Disconnected] DVD player is HP dvd640
[Disconnected] Hard drive is Seagate
ST31600 SATA


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## dai (Jul 2, 2004)

replace the psu

http://www.newegg.com/Product/Product.aspx?Item=N82E16817139004&Tpk=corsair+550w


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## Tyree (May 10, 2009)

The 650W is on special for the same price.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139005


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## Watchworks (Oct 4, 2009)

dai said:


> replace the psu
> 
> http://www.newegg.com/Product/Product.aspx?Item=N82E16817139004&Tpk=corsair+550w


Thanks for the advice. I'll go buy a power supply today.

Probably won't go for such a nice unit as you suggested -- at $99 and 550W I think that is more PSU than needed for this 5 year old PC with minimal components and original PSU of 300W (NOTE: correct model number is HP-D3057F3R). For $50 less is the next model down CORSAIR CMPSU-400CX 400 (see comparison of the original and these two CORSAIR models at http://www.newegg.com/Product/Produ...2E16817139005,N82E16817139008,N82E16817174026).


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## dai (Jul 2, 2004)

is your system pcie or agp


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## Watchworks (Oct 4, 2009)

dai said:


> is your system pcie or agp


No AGP, 1 PCIE (empty; using onboard video graphics card). 

Full motherboard specifications include the following information on expansion slots. All are empty except PCI3 (see the schematic and photo on motherboard specifications page), which has a modem.



> Expansion Slots
> 
> * One PCI Express x16 graphics PEG slot
> * Three PCI slots
> ...


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## dai (Jul 2, 2004)

then the min is

http://www.newegg.com/Product/Product.aspx?Item=N82E16817139004&Tpk=corsair+550w


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