My computer stopped working. I’ve narrowed it down to the power supply or the motherboard. The PS delivers the right voltages, but I can’t load it enough to test at rated current (12A). (I’d need a 1Ω 150 watt resistor.) I hooked it up to my heat gun, 10Ω, and it delivers 1.2 amps to that, but that’s the biggest load I have in house.
Then I remembered my pickup’s headlights: the high beam is 65 watts, about 5Ω - 5.5A; I think that’s a big enough load. But I think that’s when it’s on, warmed up, that it draws a lot more current to get warm first.
The computer power supplies that follow the ATX convention output +3.3V, +5V, +12V, and -12V, and it’s all DC. Does you heat gun function normally with DC verses AC?
Most Power Supplies that fail, FAIL… usually one for more of the fuses, bridge rectifiers, diodes, or a field-effect transistor (FET) dies or they burns up ( and you usually can smell something strange )
But when this happens, it’s not intermittent and it fails completely, if you are still getting the specified voltage from the various plugs; it’s working…
Have you eliminated all other possibilities, loose connections, bad cables, depending on the age and make of your mother board, some odd ball MBs stopped booting if the clock battery died since it did not get a time sync?
Finally, if you decide trying to track down the problem isn’t worth it; it’s a great time to buy a new computer, it seems that all the major big box stores are already advertising early Black Friday sales…
The motherboard IS the load (along with all the other devices connected to it). Who cares if it can deliver full rated current. If it’s connected to the ACTUAL load and the voltages are correct but the computer still won’t fire up, you need to start looking elsewhere.
The fans spin up; the power LED flashes, then it turns itself off.
It delivers 1.23A @ 12 V, .51A @ 5.08, .31 @ -12V (! - it’s rated to only .2, so I overloaded it. And it’s only for the serial port, which I don’t use.) - why check the fuse?
It’s not ATX.
The PS testers others have recommended just put an LED across the outputs; they agree with you.
Yes. It happens even if I remove the motherboard from the computer, take off the RAM, take out the CPU, disconnect every cable that connects to it. That’s what I meant when I wrote that I had narrowed it down.
Big spender.
It fires up, then powers down, then restarts, every 5 seconds. It acts like a device that has exceeded the rating of its power supply
New ones run $70-$120. I can buy an untested used on eBay for $14. I can buy a barebones computer of the same model for $26 - and it’s been tested.
I got my computer support from LinuxQuestions. I asked about using a headlight as a load. That’s the question I asked here.
Fun. If responding wasn’t fun for you you shouldn’t have.
Heh heh. My last computer was a thermotake. The fans were so noiseyz I had to replace them. When the machine went south, Dave wouldn’t work on it so I just bought a new computer. Those magnets in the hard drive are something to behold.
Super magnets they are, I have a bunch I harvested at work. The interesting thing is they are super strong magnet on one side, then nothing on the other. Looking to build a perpetual motion machine.
I use several discarded car headlights to load- test computer power supplies. In this area folks throw their computers away all the time. They just put them out on the curb for anyone to take. If I need a lab power supply for some reason I’ll grab one, take it home & and extract the power supply, easy-peasy way to +/-12, +5, +3.3 vdc, delivered at a considerable power rating for the lab bench. BTW, this method isn’t entirely safe. Old computer power supplies may have high leakage current. I always measure the leakage current before using them.
Thanks. It’s the wrong footprint, expensive at $27.50.
I have an SSD now. It’s worth the money, not that I paid anything for it.
DING! DING! DING! We have a winner. Thanks, @George_San_Jose1 . What resistance do they measure cold? I worried that they could be 1Ω, draw down a computer power supply enough to cause it to shut off before the bulb warmed up enough to raise the resistance to operating.
What happens to the supply output voltages when this happens?
Normally, when you initially apply power to the computers I have with soft start, they will do exactly this and then immediately shut back down. When you press the power button, it then wakes up and goes through the normal boot process. There could just as easily be something wrong with the soft start circuit making it look like the button is continuously pressed. But diagnosing it while connected would be the route I would take.
I come here to contribute because I find it fun and occasionally I may even help someone. So doing all this extra work that may have no diagnostic benefit is fun for you? Great, have at it. I thought you might be interested in solving a problem in the most expeditious way. I find fixing things generally fun but I usually don’t perform diagnostics for fun. Carry on…
It’s difficult to measure low ohm’s accurately , but my estimate for the cold filament of a 9001 bulb I test with is 1/2 ohm. I think that’s the high beam, but not sure. My power supply has no trouble with lighting it up on the 12 volt lead. It has these power outputs
They rise to rated value, then fall off to near zero, then start over.
Some this computer lacks.
The power button doesn’t matter. I disconnected it: the same happens.
I started this on LinuxQuestions. Only after mulling it over did I realize I had only one load below 10Ω that would handle the current: an auto headlight. I’m pretty sure it’s the motherboard; contributors on LQ lean to the PS. I wanted to answer the question, not just fix the problem, and at the least cost. It would be elegant to replace the PS for $14; it would be more expensive if wrong.
The simplest test you can do is to disconnect everything from the PSU. Does your PC cabinet have a secondary fan? You can reconnect this fan or use one of the auxiliary devices as a load on the supply. Look at the motherboard connector from the PSU. The single green wire is the enable signal that comes from the motherboard to the PSU. Use a bent paperclip to connect the pin with the green wire to any black wire pin in the connector. Now try powering on the supply. If it turns on and runs its own fan and the load fan/device without cycling on/off, the problem may be elsewhere. If it still cycles, the power supply is bad.
Are you able to measure the 3.3V 5V and 12V supply Voltages while attempting to turn the computer on? Most people just swap in a different known good power supply to test to see if it’s the board. Power supplies are supposed to have a minimum load on each output. Usually you can get away with not doing that, but I’ve blown out the 3.3V regulator by loading down the 12V and leaving the rest disconnected.
You said a regulator on the motherboard is bad. That’s quite possible. It could be the power supply for the CPU or memory.
