I) Let's start with the Dell. The computer was subject to a power surge
caused by lightning. You have replaced the PS with a new power supply.
When you press the case power switch nothing happens.
1) Check that the PS is set to the proper voltage and plugged into a
known good AC source and that the PS switch is turned on. Unplug till
item 6.
2) Check that the case power switch is properly connected to the
motherboard.
3) Check that the 20 pin power connection to the motherboard is properly
connected.
4) Check that the 4 pin power connection to the motherboard is the right
one and that it is properly connected. If the motherboard does not use
the 4 pin connection, this item does not apply.
5) Have no other items connected to the computer, the motherboard
including cards,RAM and CPU, and the power supply.
6) Momentarily press the case power switch. The PS fan should come on
and, if the motherboard is equipped, the green LED on the motherboard
should light.
7) If nothing happens, try reversing the orientation of the case power
switch connection to the motherboard.
8) If nothing happens, either the case switch is bad or the motherboard
is bad. OR The new power supply is bad out of the box. For a test of the
power switch and since they are both momentary contact switches, you can
temporarily substitute the reset switch for the power switch using the
connection at the motherboard. If needed, you can buy a power switch
replacement.
9) If the PS fan comes on and, if equipped, the green motherboard LED
comes on, start rebuilding your computer one item at a time. There are
several good web sites with step by step directions on building a
computer. If I start with known questionable components as you probably
have after a power surge, I always test my build after each step even
though it is more time consuming. That way it is a lot easier to
identify any bad components.
II) Now let's go to the HP. The PS "tests" good on a tester, but when
connected to the motherboard and the case power switch is momentarily
pressed, the PS fan does not come on although the PS is supplying at
least 12v power because the CPU fan comes on. I've never run into this
before, but I would try to isolate the problem. I would try the above
steps with the existing PS. If the PS fan still does not come on after
step 7, replace the PS with a known good one and repeat the steps.
a) If the current PS fan works, keep going on the rebuild one step at a
time. Reset the BIOS/CMOS by removing the battery on the motherboard for
about a minute and then replace it back on the motherboard. If your BIOS
is not corrupted, this action will reset it to the default settings. If
your BIOS is corrupted, you will need to either replace the BIOS chip,
get a replacement motherboard, or consider replacing the computer.
b) If the current PS fan does not work and the known good PS replacement
fan does not work, the problem is most likely in the motherboard. You
will need to replace the motherboard or replace the computer.
c) As I remember your previous posts, the motherboard may not be the
only problem and repair costs will start mounting making the computer
replacement option more advantageous. And you might be able to use some
components of the HP in the rebuild of the Dell (compatibility may be an
issue).
I hope this helps.
Tom Mayer
Russ Cox wrote:
> I have two computers (one HP, one Dell) that will not power on. The
> Dell suffered from some lightning effect, but nothing obvious. The HP
> went thru a series of "freezes" (HP Toast? update) before a freeze
> during flashing the BIOS killed it. Both power supplies test good, all
> voltages present and the PS fan runs when plugged into the tester.
> When I plug the PS back into the motherboard and press the Power on"
> switch, nothing happens on the Dell. On the HP, the CPU fan comes on
> but not the PS fan. +5v is present on both units since the mobo LEDs
> are on.
> The power switch on the HP does close when pressed as checked by
> ohmmeter. Didn't check the Dell. All cables are in place on both
> units and not damaged. I thought the power was turned on by the
> momentary ground applied from the power switch to the "Power Good"
> line (pin 8 on the 20 pin power connector) to the PS. It appears
> the power supplies are good, but something isn't working. I did try a
> new PS on the Dell, same result.
> I must be missing some step in this analysis. But I'm trying to figure
> out what failed.
>
> The NOSPIN Group has added a new feature on our website,
> web based bulletinboard for questions and answers:
> Visit our sister website at http://nospin.com
>
>
>
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