Resolved Motherboard or Power Supply....

0I am working on a friends computer and his problem is as follows: He told me his computer wouldn't power up, no lights , no noise. I have it here now and this is what I've found. When I jumper pin 16 to GND the Hard Drive spins up, the DVD player comes back to life and the PSU Fan starts singing, my concern however is that neither the CPU or Sys Fan will come back on. They are both 3 pin and I wonder what the voltage should be. On the CPU fan I'm getting @ .375 volts. I'm pretty certain it's the mobo (screwdriver to the soft power jumpers doesn't seem to work either), any recommendations before I advise him to turf the mobo?

HP Pavillion with a MCP61PM-HM (Nettle 3) motherboard (none of the capacitors, upon casual observation, seem to have ballooned or ruptured, as seems to happen with some of the Chinese manufactured boards from HP.

Also, no new hardware.

+/- 12, 5 and 3.3 are all within tolerance

Bare mobo with no HDD, RAM etc etc, same issue.

The only other computer I have in my office right now is a laptop, so I don't have any other PSU's to test with.

Thanks in advance.

 

I would try another PSU before the turf. Cheers Neil.

 

Yep. It sounds like you are missing the +12V. Here's my canned text on testing PSUs:

To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

Fortunately, there are other options that are almost as good. I keep a FrozenCPU Ultimate PSU Tester in my tool bag when I am "in the field" and don't have a good spare power supply to swap in. While not a certain test, they are better than nothing. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within specified ATX Form Factor Standard tolerances. Lesser models use LEDs to indicate the voltage is just within some "range ". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed ". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, it is not a true load or suitable for conclusive testing.

Note the required voltage tolerance ranges:

[size= "1"]NOTE: Disregard the -5VDC reading. It is no longer used.[/size]​

Swapping in a known good supply is a tried and true method of troubleshooting used for years, even by pros. If you have access to a suitably sized, spare power supply, carefully remove the suspect supply and replace it with the known good one, and see if the problem goes away.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This requires poking (with some considerable force) two hard and sharp, highly conductive meter probes into the main power connector, deep in the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it. It is not worth the risk considering most multimeters, like plug-in testers, do not measure, or reveal any unwanted and potentially disruptive AC components to the DC voltages.

And remember, anything that plugs into the wall can kill. Do not open the power supply's case unless you are a qualified electronics technician. There are NO user serviceable parts inside a power supply.​

 

Thanks for the suggestions, I replaced the motherboard and it came back to life, needing a Windows 7 reinstall for some reason. Pardon the delay in closing the thread.

 

Thanks for the followup.