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Weird PSU symptoms


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#1
iPowerUser

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Hey fellow geeks - I recently just did some hardware modifications to an old Windows XP box to setup as a machine for me to get some hands on practice with for my MCDST exam. It's about 3 years old, an HP Desktop with 512MB of RAM, 120GB HD, 2.60ghz Pentium 4 processor, etc.

I opened it up and added an additional 512MB of RAM, added another separate 320GB HD and replaced both CD/DVD/RW drives. The machine booted up OK before doing these basic mods. I have double checked and tripled checked that all pin connectors, wires and miscellaneous cords are fastened tightly and in the appropriate ports.

Now the machine won't power on at all. Before doing these mods, I could boot into the OS no problem. The power supply led light illuminates once I plug into the wall outlet. However as soon as I press the PC's start up button, the power supply light quickly goes out and I hear no fan noises or anything indicating the box is getting power.

I really doubt the power supply died because it was working fine before the hardware mods. Maybe something happened inadvertently to short out? Do power supplies need time to charge after unplugging connectors for a brief time? I've ruled out some basic things, and I'm relatively tech savvy.. are there any solutions besides changing the power supply?

Thank you for your time and solutions!

Edited by iPowerUser, 14 November 2009 - 05:01 PM.

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#2
Neil Jones

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Bearing in mind the most strenuous part of being a PSU is the initial power-up sequence from a cold start, and hard drives suck up most of this getting started, it's perfectly possible the PSU now can't provide enough juice to get everything going. Those HP ones tend to be Bestec with low wattage output, but it's worth replacing just by virtue of the fact that's a Bestec, they tend to go bang rather spectacularly after three years and take the entire system out with them.

I presume you have replace the PSU?
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#3
iPowerUser

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I was trying to avoid spending any money on this practice junk box, but I guess that's going to have to be necessary Neil. I just threw some spare parts in and hoped for the best. However, I did leave the PSU plugged in overnight so it could try and hold some voltage.. only to turn the box on this morning and have it do the same thing. I think the low wattage won't sustain the 2 HDD and other hardware upgrades I made.

I'll update the thread after I drop a new PSU in, hopefully that'll do it. Thanks!
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#4
iPowerUser

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Just added a brand new 400 Watt PSU to the desktop and nothing is turning on, not even the new PSU. Anyone have any ideas?
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#5
rshaffer61

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IS the outlet live?
The connections to the mobo correct?
IS the switch on the front connected tot he MOBO correctly?
Have you tried to do the following?

Disconnect everything from the Motherboard except
  • keyboard
  • mouse
  • video output
  • 20+4 powercable
  • 4/8 pin 12v wire both coming from the powersupply,
  • Cpu fan wire
  • power and reset button to the case
  • case speaker
Now you should have NOTHING connected to the motherboard except what was listed above.

The goal here is just to test the mobo:

If the computer still will not boot up then we need ot take a look at the modifications you did.
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#6
iPowerUser

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Hi and thanks for your help!

The outlet is live, I know this because the LED on the back of the power supply lights up. However, nothing inside the box seems like it's responding. I tried with both a brand new PSU and the existing PSU source.

As far as I could tell, the configuration inside the desktop was connected correctly, but there's always room for human error. So I went back and followed your directions and unplugged everything from the mobo except what was listed.

I'm still not receiving any type of activity from inside the box.. except the PSU's LED green light is still illuminated while being plugged into the live outlet.

Pressing the power/reset button yields no activity or boot sequence. It's wire is correctly plugged into the port that reads "PWR LED RESET" on the physical mobo itself.

Edited by iPowerUser, 15 November 2009 - 02:00 PM.

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#7
rshaffer61

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It is beginning to sound like a bad MOBO.
I would triple check that switch connection to the MOBO from the front of the case.
Did you disconnect the 320 gig hd?
Try taking out one stick of memory or put old memory back in.
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#8
iPowerUser

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I removed the new memory stick, leaving the remaining 256MB sticks that originally came with the box. Each stick is in a blue slot parallel to an empty black slot.

The only other switch connection in the vicinity on the mobo says "FRONT USB1" and "FRONT USB2", so it obviously couldn't be those two since there are two USB 2.0 ports on the front of the box.

I disconnected the master/slave IDE wires from both 120GB and 320GB hard drives and the mobo.

Also tried booting with the stock ram and HD config, no luck.

This box was just working yesterday. I DBAN'd the HD and was going to reformat with a fresh OS install. I opened it up, added the 320GB HD and 512MB ram and now it won't even turn on.
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#9
rshaffer61

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The other option is to take the MOBO out and do a bench test. If it fails to start then we can only determine that the board has died.


Remove the motherboard from the computer along with the power supply

place the motherboard on a piece of card board larger than the motherboard,

this will eliminate a short from the mobo to the case which could be a possibility
Install the cpu with, 1 stick ram in dimm 1, power supply, case switch and case speaker
Connect ps2 mouse and keyboard along with the monitor
Repeat the above and power on
If the computer now boots into bios you most likely had a case short so make sure when installing the motherboard in the case that you use standoffs and they line up with the mounting holes in the motherboard and none of the standoffs touch anything else on the underside of the board.
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#10
iPowerUser

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Having issues removing the motherboard from the chassis. The 120GB is also blocked. I can't access the other side of the box as it's also blocked off. The last few screws are hiding behind and under some metal insulation as pictured. Any suggestions?

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#11
rshaffer61

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Looking, give me a little bit to look this all over.
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#12
iPowerUser

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No problem.. it's an HP m376n box. It's an old junk box, so I kind of expected to run into some bad engineering.


UPDATE: Plugged the old PSU into a different mobo and the mobo LED lights up. Had to use a different power/reset switch, still wouldn't boot.

Then used new PSU into different mobo with power/reset switch, no LED lights up and also wouldn't boot. Strange.

Edited by iPowerUser, 15 November 2009 - 04:03 PM.

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