Bad PC PowerSupply or MotherBoard?

snipped-for-privacy@yahoo.com ha escrito:

You got it backwards... you can blow a good motherboard with a bad PSU, but not the other way around. In a properly designed PSU, if the motherboard is shorted, the PSU will refuse to start, and nothing will be damaged.

Since all the components you tested are ok, the next thing I would do is to try a new PSU there.

snipped-for-privacy@yahoo.com wrote in news:1149373802.041400.159020 @i39g2000cwa.googlegroups.com:

check the motherboard for bad capacitors, they will likely have bulged tops (domed instead of flat) or leakage. That is the most likely problem from the description given.

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snipped-for-privacy@yahoo.com wrote in news:1149373802.041400.159020 @i39g2000cwa.googlegroups.com:

I'd not worry about it too much. If you blow the motherboard, don't worry, it's a Compaq. (In my experience, Compaqs are only good for parts machines. They're junk otherwise.)

You can get power supply testers and the like, or simply plug a drive in to the power supply and start testing output voltages. Also, with the PS off and unplugged try measuring resistance between supply and ground (+ and -). There should be some resistance, most power supplies that die are designed to switch every output to ground when they do.

Puckdropper

lsmartino,

What about repairing the old one? This is a learning project so I would like to know what killed the original PSU.

Also thanks for correcting my errors.

Ken

You don't indicate symptoms. I'm guessing no power / zero response when power button is depressed.

You didn't say whether you tested continuity of the momentary power switch. Wouldn't that be a quick fix? You can follow the wires to the MOBO, disconnect the switch connector, and jump the two pins on the MOBO momentarily with a small bladed screwdriver.

An ATX power supply won't start without a ground signal supplied by the MOBO. If you want to test the power supply, do this... Remove all connections except 1 drive. Doesn't matter which. You have to leave a load on it. With the 20 pin MOBO connector in your hand, jumper pin 14 ( light green ) with pin 13 ( black ). The power supply should start. If it doesn't, it's broke. If it does, you can perform pinout tests by following a chart obtainable from a zillion sources by Google-ing 'ATX Pinout'.

My best suggestion is to sub a power supply. That is a quick & dirty test that usually tells the story. I don't recomment attempting a repair on a pc power supply for two reasons:

It would be a shame to have lucked a blown PSU without MOBO damage only to fix it and have the PSU wipe everything out a month later. They usually fail with all the fire, smoke, noise and theatrics of a good stage show - they don't usually just quietly blow a fuse.

Good luck.

I have the same problem: when I pressed the power button - nothing happend. This motherboard (with integrated CPU) was working on old computer the day before, but today, on the second comp., she don't (the same PSU). Can mobo colapsed if speaker (beeper) was connected wrong: pins 1 and 4 are wrong, 3 and 4 are correct. In the first moment speaker was connected at 1 and 4 (pin 4 is +5V) ???

If you were hooking the speaker to a 4 pin speaker connector, I don't think you caused failure. If Pins 1 & 2 are for something other than the speaker, then you'll need to clarify the purpose of those pins for better feedback.

I am guessing that you removed the motherboard from one case and installed it into another case? If this is what happened, there is a very real possibility that you have created an open on the mainboard. I have seen this a number of times. A board is perfectly fine till someone snaps an additional memory module in, plays with an IDE cable, inserts a PCI card, or any other operation that causes the board to flex. At that moment, a circuit buried somewhere in the laminated circuitry that was making contact through gravity and magic is disturbed, never to find continuity again.

When dealing with PC mainboards, leave sleeping dogs lie!

Bob

Correct

Will Do. If it starts do I immediately remove the screwdriver?

Just to make sure I have it correct. I remove the MOBO harness and only leave 1 HD connected, then jumper 13 and 14. If starts PS is OK.

Thanks much for the detailed tips!!!

Ken

Bob,

"With the 20 pin MOBO connector in your hand, jumper pin 14 ( light

Forgot to ask, what to you use to jumper 13 and 14? Also am guessing that these 2 wires are low Voltage and Amp so there is No personal harzard?

Thanks again for the detailed tips!!!

Ken

Yes - remove the screwdriver. It's the same as pressing the button on the front of the case. Apply the short, then release. The trick part is making sure you hit the correct pins and ONLY the correct pins.

I use an unfolded paperclip to jumper the two wires together. It is low power and poses no hazard. If you really want to play it safe, hold the paper clip in a hand protected with a heavy work glove. Again - make sure you jumper the correct pins - black wire and light green wire.

Bob,

Thanks again for the paper clip tip! Jumpered #13 and 14 as you instructed. When connected the PS power cord to an AC extension cord heard a faint hi freq sound but no fan sound/movement or hard drive sound.

To double check I then jumpered a Good PS and again connected the cords. This time the hard drive and PS fan started.

Guess now is the time to try the Good PS with the Compaq MotherBoard.

Question, what if the Compaq PS when it died damaged the MotherBoard? Is it worth checking the MotherBoard for shorts etc?

Ken

It's possible that the PS damaged the motherboard. I'm sure there are tests that you can do as a preliminary. I've never bothered. The only real way to know is to hook it up and let it fly. My bet is that it will fire up and run fine. 99% of the time they do. If the board is blown, you'll cause no further harm by hooking up a good power supply. It's already junk. The board won't likely hurt the power supply.

Bob Kos

Finally put tried it. Guess I got the 1% because when turned it on, the hard drive and CPU fan started but the monitor screen was dead. Also there were no beeps or any soundswhen started. This MoBo has internal graphics so decided to install a real PCI graphics card. Same thing.

Guess the only thing left to test is the CPU. Am wondering what is the % that the CPU works when the power supply damages the MoBo?

Ken

tests

way

and

no

Do you know that the replacement PS is good? I suspect that it is, but I got burned that way once so it comes to mind.

It does sound as if the mainboard is bad. I have seen bad motherboards take out processors on two occasions. they were both AMD Athlon machines. I don't know that the Athlon being both instances is relevant. I have seen twice where boards took a lightning hit in through the AC line & out the modem / phone line without damage to the processor. Those machines were both Pentium I machines. Both smoked the motherboards & power supplies. As such, I think it's a difficult call without knowing EXACTLY what went bad on the board.

Unfortunately, you are now in the position of having to access another machine to test your processor. What kind of processor is it?

One other free thing to try. And I don't know why this has worked for me but it has. Clear the CMOS. Take the battery out and apply the CMOS clear jumper. Then put everything back and see what happens. The CMOS may have been scrambled by some sort of overcurrent condition that happened when your PS went bad.

And as I have just found recently, don't forget to look for bulging , leaking, or otherwise deformed capacitors. The PS failure might have been enough to push a marginal cap over the edge. Apparently there was a rash of defective electrolytics that made their way onto mainboards a few years back. I just opened a board up with 13 leaky / bad caps.

Bob Kos

There have been 2 PSes tested with this MoBo. One was a New Compaq and other a New std ATX PS neither started the MoBo.

My question is how to find what went bad with the MoBo?

Maybe I am Lucky on this, it is an Intel Celeron.

Thanks for the CMOS tip will try! If you remove the battery will the CMOS clear itself? This Mobo had been without a battery for a couple of months before I got the PC.

I have looked but so far have not seen any leaky or bulging caps. Am wondering if the caps may be bad but at this time am not too anxious to pull all the caps just to check.

Ken