Member Avatar for Sycophant

Hi.

I have a Compaq Presario 6000 PC with a P4 2.53 ghz processor that rendomly started booting and dying all on its own the other day. I work on my laptop and this machine is used by the wife for internet and games.

I opened the case and started to look at things. The first thing I looked at was the power switch, which when connected to the board while the box is plugged in will result in random start/stop activity - even without user intervention. I got the machine totaly booted and shut it down, powered off and unplugged. I disconnected the power switch from the board and plugged the machine back in, and the behavior stopped. Now here's where I screwed up (I'm a half assed hardware tech, I break more than my fair share of stuff this way) but I plugged the switch back in while the power was still plugged in and it fired up, but my snap reaction was to pull the switch connector again (You plug something in and something whirs, sometimes you justundo what you did.) Strangely, the machine booted up the first time, all the way, and stayed on (which it hasn't done for a while with the switch plugged in). So, knowing that I could short something out, I shut down the box, unplugged the power from the PSU, and plugged the switch back in. I plug the box back in and without pressing the power button it starts to switch on again. It goes through a cycle of off and on and never actually boots up all the way, finally it shuts off and I pull the plug just as it's coming back up (This is a very rapid boot/stop/boot/stop sequence, sometimes it powers up all the way to the windows loading screen, sometimes it doesn't make it past the bios setup screen). I'm thinking that this is either a short in the switch, or a short in the board where the switch is connected.

Any ideas?

Mike

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Dani AI

Generated

As described, the machine repeatedly cycles when the front-panel connector is attached. and raise reasonable points about the switch and connections. To avoid replacing parts blind, use this targeted, non-destructive sequence to isolate switch vs. PSU vs. motherboard short.

  • With the PC unplugged, visually inspect the board for bulging/leaking capacitors, scorch marks, or misplaced standoffs that could short the PCB.
  • Test the front-panel wiring: with the connector unplugged from the board, use a multimeter on continuity across the switch while pressing it and while wiggling the cable. Intermittent open/close readings point to the switch/cable.
  • Bypass the switch: with the PSU plugged in and everything else disconnected, momentarily short only the two power-on pins on the front-panel header (insulated tool or jumper) to simulate a button press. If behavior changes, the switch/case wiring is implicated; if cycling persists, look elsewhere.
  • Check PSU behaviour standalone: start the PSU by shorting PS_ON (green) to any ground (black) and measure the rail voltages (3.3V, 5V, 12V) and 5VSB (purple to ground). Unstable or missing rails under no-load indicates a PSU fault.
  • Reduce to minimum hardware (CPU, one stick RAM, onboard video if available). If the problem disappears, reconnect devices one at a time to find the load that trips it.
  • If the system sometimes boots to Windows, review Event Viewer/ Reliability Monitor for unexpected shutdown events to identify thermal/power events.

Cautions: always unplug mains before moving jumpers or unplugging connectors and avoid bridging adjacent header pins. If tests point to the PSU or foundered capacitors, replace the failing component rather than running the machine while it cycles.

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Member Avatar for The New Normal

Have you tried plugging the switch in the motherboard the other way? They do have + & - on them. Maybe you're putting it in the wrong way...
Check your mobo manual for the correct way to put it in. The plug should have a + & - written on it for you to match to the manual.

Otherwise it does sound like either a voltage issue of some sort (something taking too much power) or a loose connection. I suppose it could be a flat BIOS battery, but I can't say for sure as mine has never gone flat...
Perhaps check to make sure all plugs are connected firmly.

Member Avatar for coolraj003

I am thinking its the power switch thats the culprit here. Try changing that cos the way you are describing the rapid on and off of your system that would not be very healthy for the mobo's life. I would try changing the power switch and sort this problem out before letting it play with the system.

Raj

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