Computer Power Supply Question

[wb6bum]

I have an HP PC that for quite a while has served me well. Lately, it won't start up in the mornings. Gives a short effort, and then loses interest.
However, if I pull the AC supply, and then re-insert it, she starts up just fine.

This seems to have started after we had a series of power blackouts up here in the mountains, but that might be coincidence.

Any ideas?

[WA7CC]

Is the computer starting from hibernation or full shut-down?

Have you tried booting from a floppy disk or CD to see if you have some sort of hard drive problem?

Tell us more about what happens as the computer fails to start.

[wb6bum]

Full shut down. The lights come on, the hard drive spins for a few, then she just loses interest and shuts down.
But pull out the plug, and put it back in, and Presto! Just like new again.
:mad:

[KL1ZB]

When this happens try holding the power button in for a 10 seconds then push it again see if it will boot after that.

Also, you might try replacing the bios battery, its a long shot but I have seen systems do stranger things then that when that battery is dead or near dead.

[W2ILP]

All computers now use switching type power supplies. They rectify the AC and voltage double it and then they switch it with a pair of solid state devices so that it can be transformed and filtered with small components.

It is possible that you power supply doesn't start switching every time that it should. You would need a schematic diagram to find out which component (s) might be the cause of the switching (chopping) components possible failure to start.

Computer power supplies are not very expensive and you might easily get one from someones old computer, which will be a good replacement....or at least a substitution test to see if the power supply is really your problem. Most computer power supplies have the same color coded leads going to molex connectors for + and - 12 Volts and + and - 5 Volts. Newer supplies also have + 3.3 Volts. Newer supplies are soft switched on by a keep alive circuit, which might also be a cause of trouble. This circuit is "on" as soon as your computer is plugged into the AC line, it is then under the control of mother board software.

I hope that this is of some help.

BTW...I don't call them power supplies anymore. I call them energy converters.

w2ilp (Instantaneous Limited Power) is not enough. You need energy not power because that means Watts per time and not just potential Watts. A computer power supply does not supply power or even energy...It can only convert some form of energy into a form of energy that you need.

[KG4CGC]

Check all your cables and jumpers by hand.
Power outages are hell on power supplies in computers. You'll probably end up replacing that power supply and getting a line filter and back up power device in one. Also, it is likely that you have a 300 watt ps in that HP. If you add any parts like an upgraded video card and another HD, you are already overstressing an already stressed ps.

[KC9JIQ]

wb6bum, what is that kid doing in your avatar? Looks dangerous!:eek:

[w1tdp]

Not to say this is your problem, but my HP 771N was doing the same thing a while back. Many calls to HP provided no help, and to tell the truth I can't remember how I discovered the problem, but it truned out the power on push button was stuck in the "pushed" position. For the longest time I was too lazy to take the switch apart and clean it, I just left the case off with the switch unpluged from the mother board and jumped the two pins on the board to start the computer. Funny now that I look back on it!
Try starting the computer as you always do and then unplug the switch leads from the mother board. If it boots up, you have found the problem!
Good luck.

73

Edit to add: BTW, you can't tell it is stuck by looking at the front of the computer, because the plastic button is connected to the switch by a linkage. The button on the face of the machine can look to be in the normal position and the actual electrical switch still be stuck.

[w9gb]

Keeth -

Two possible causes.

1. Your switch-mode power supply is slowly failing. I have seen these symptoms on my computers as well as others. IF you have another computer power supply to use as a substitute -- that is a quick way to diagnose.

2. The other is that you have a motherboard with leaking or failing electrolytic capacitors.
Before you decide your caps are bad, ALWAYS try a known good and high quality power supply.
You can read about BAD CAPS here:
http://www.badcaps.net/pages.php?vid=5

I have repaired computers with BOTH of these issues.

**Looking for a QUALITY substitute power supply? **
PC Power and Cooling have been in business since early 1980s -- supplying quality switch-mode PC power supplies.
I have purchased from them since 1983 ..... that length of time in the PC business is due to their quality and they have
earned high respect in the industry!
http://www.pcpower.com/index.html

w9gb

[n8yx]

wb6bum, what is that kid doing in your avatar? Looks dangerous!

Looks like he's trying to 'channel' an RCI radio to me. ;)

To the subject at hand:

'GB's correct - your switching PS is on the way out. I would also suspect a bad cap or possibly one of the feedback resistors has begun to drift in value...

[KD8HMO]

Also, I have found this twice now. Check to make sure all of the mounting screws that mount the computer board to the case are TIGHT. That is where the board is grounded. I have found two that were acting strangely, and their mounting screws could be turned with a fingernail, not tight at all. I tightened them up and good as new.

[WA9SVD]

Either the supply is dying (most likely) or some device (hard drive, CD/DVD Drive) or component is placing an intermittent high load on the supply at start-up.
WHat is the "power" rating of the supply, is it AT or ATX type, and what type of H-P is it? (Processor, speed, drives, age) may tell us more. Have you added any hardware (or replaced hardware) recently? If so, the supply may be overloaded.
If you can swap supplies, that's probably the easiest and fastest way to troubleshoot.