Member Avatar for news_shooter

Having a strange problem with my Compaq Presario/AMD Athlon (1.5 yrs old). As long as it's running, everything is fine. But, if you shut it off, for any reason, and pull power, even for an instant, it won't restart.

Looking at the power supply on the back, I noticed that the power led (on the power supply) was blinking intermittently. So, I plugged in a spare (working) supply, to no avail. But, I put AC back to the old (still installed) supply, and the light came on.

Through trial and error, I learned that, when the motherboard power connector is plugged in, the computer simply won't start (no lights, no noise, NOTHING) and the power supply led blinks. But, unplug that, and the light is on.

Just to see I tried plugging in the motherboard cable with the AC connected. Okay, not the brightest thing to do, but I wanted to see, and sure enough, as soon as you plug in the connector from the motherboard to the power supply, the light goes to blinking. Note that it's not like an "error code blink", just an intermittent flash of varying intensity.

If you plug and unplug the AC cord a few times (tried 2 ac cords to eliminate that problem) the light will finally stay on, and the computer will work fine, until the next power flash.

I figure I can either puzzle this out, or just go buy a battery backup:-)

TIA
Jim

  • 2 Contributors
  • 3 Replies
  • 113 Views
  • 1 Day Discussion Span
  • Latest Post Latest Post by Thong_Ispector

Dani AI

Generated

A few safe, practical diagnostics and explanations to follow before buying parts. As describes a unit that powers normally until the motherboard is connected, and as cautioned, do not make a habit of connecting or disconnecting ATX plugs with mains present — that can damage components.

Start with these non-destructive checks:

  • Power off and unplug. Do a close visual inspection of the motherboard and the supply for bulging or leaking electrolytic capacitors, burn marks, or loose screws/standoffs that could short the board.
  • Test outside the case: mount the motherboard on an insulated surface (cardboard) to rule out a short to the chassis.
  • Reduce to minimum: disconnect all drives and remove all add-in cards; try POST with CPU, one stick of RAM and video only if required.
  • Check the PSU separately: verify the standby rail and that the supply runs when told to (use a proper PSU tester or a multimeter if comfortable). Note that some modern supplies need a small load to regulate properly.
  • If a known-good PSU behaves the same when connected, the motherboard or a short is the likely culprit; if a different PSU works, the original supply is suspect.

Why this happens (brief): modern PSUs have protection circuits that shut them down immediately when they detect an overload or short. A failing capacitor or a direct short on the board will trip that protection. Repeated plugging/unplugging can let the supply reset temporarily but does not fix the underlying fault.

Recommended next steps: replace the CMOS battery only as a cheap preventive step, but prioritize the visual checks and the bench testing sequence above. If uncertain about live-voltage checks, have a local repair shop perform the PSU/motherboard isolation tests — they are quick and will save unnecessary parts purchases.

Recommended Answers

All 3 Replies

Member Avatar for Thong_Ispector

First of all STOP DOING THAT...
You will blow up something important.

Although a year and a half isnt old I would check your cmos battery, replace it if at all questionable.

What was your original power supply rated at?
What was the rating on the power supply you tried?

Did you add anything to the original configuration, drives, ram, or upgrade the video card?

Member Avatar for news_shooter

The original was a 250 watt p/s, while the replacement was a 400 watt. I hadn't thought about the cmos battery, I wonder if that could make it do this-well, it won't be too hard to replace that.

Nope, I hadn't changed anything from the stock configuration. I'd added a Pinnacle capture card the day I got it, and hadn't done anything since.

I know that doing the "plug it in" stunt isn't the brightest, but it's not likely to damage the hard drive itself, and I figure the motherboard is already toast. I found a direct replacement motherboard online for seventy bucks, so that's my first inclination.

Member Avatar for Thong_Ispector

A direct replacement would not be my first choice.

For about the same money you can get a new case with power supply and a new MB that will take your CPU and other components.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.