Re: What's your best guess?

On Oct 7, 11:20 pm, Larc <l...@xxxxxxxxxxxxxxxx> wrote:
Wire-------------Power on, but PC not-----------------PC turned on
Orange (+3.3V)-----------0V--------------------------3.356V Steady
Red (+5V)-----------------0V---------------------------5.11V Steady
Yellow (+12V)-------4.6V ~Steady--------------------12.06V Steady
Gray (Power Good)---.4V to .5V------------------------4.92V Steady
Green (Power On)--------0V----------------------------5.11V Steady
Purple (+5V SB)-----5.06V Steady---------------------5.06V Steady

These numbers says the power supply is perfectly good in this
computer. The red, yellow, orange, and purple wire voltages are in
spec. Purple wire is powering the power supply controller so that the
controller can see the switch pressed and can tell power supply to
power on. Controller tells computer to turn on when green wire
voltage goes from 5.11 down to near zero (I assume you have reversed
the numbers because 0 V would turn on power supply and 5.11 V would
turn it off. Also green wire voltage should not exceed purple wire
voltage). Regardless of erroneous Power On numbers, still, other
numbers says that signal is turning on the power supply.

When power supply sees the red, orange, and yellow wire voltages OK,
then it tells power supply controller "Power Good". Power Good at
4.92 V means power supply controller should tell CPU to operate. CPU
cannot do anything until supply controller says so.

The relevant power supply functions are working fine. So the power
supply controller is not telling the CPU to operate, or some other
motherboard function has failed.

Next examine the CPU power supply. In particular, electrolytic
capacitors adjacent to the CPU. This power supply creates 1 to 3 volt
voltages for CPU from the 12 volts (yellow wire) that connects near
the CPU. Tops of those electrolytics should be perfectly flat. If
bulging, then motherboard could be repaired by replacing those
electrolytics.

Possible is that a peripheral is locking or obstructing a critical
signal. Disconnect everything except CPU, power supply, power on
switch, and speakers. Even remove all memory, video controller,
keyboard, and mouse. Then connect AC power cord and power computer.
If working, the speaker should beep. If not, the CPU is not even
executing.

Also possible are motherboard PC traces shorted to metallic
standoffs. IOW the green solder mask has finally been penetrated by a
standoff (or some protrusion) and is shorting out a critical signal.
Remove motherboard and carefully examine anything that might touch
something metal. Verify standoffs only touch metallic rings around
those standoff holes.

If these obvious defects do not correct a motherboard problem, then
only option is to trash a defective motherboard. Based upon
multimeter numbers, the power supply is not defective. If the
simplest computer configuration (supply, motherboard, CPU, speaker,
and power switch) do not even create a beep, then a properly powered
motherboard is dead. Short of doing an analysis with an oscilloscope,
no further options exist other than to replace the motherboard.

Well I did that once to one motherboard. I traced the signal from
power supply controller to CPU. Found a broken PC trace under a
connector. Could not see the broken trace - only measure it.
Soldered a quarter inch jumper wire. Motherboard worked again. Well
even a single trace can fail years later causing the entire otherwise
perfectly good motherboard to fail. For the want of a nail, a kingdom
was lost. With so many things that can fail, it is amazing any
computer works.
.

Relevant Pages

  • Re: What do I need for 1080p playback?
    ... The CPU is a 1.8ghz e4300 Core 2 Duo. ... I want to buy a hi-def video camera but I need to be able to see what I just shot! ... in the socket so it cannot touch the processor. ... The wire then becomes my "overclock control". ...
    (microsoft.public.windowsxp.hardware)
  • Re: P5Q wont boot after long stable service
    ... The motherboard grounds PS_ON#, when it wants to turn on the power supply. ... (The voltage should be the same ... each pin is crimped to the wire. ... from the meter to the motherboard. ...
    (alt.comp.periphs.mainboard.asus)
  • Help! New P5K rig powers up briefly
    ... Put together my new machine based on a P5K Deluxe motherboard and a ... when I power up, the fans simply spin for a moment. ... all wire labels face the top of the case): ... Speaker | black wire ...
    (alt.comp.periphs.mainboard.asus)
  • Re: Help! New P5K rig powers up briefly
    ... when I power up, the fans simply spin for a moment. ... Ensured stock cooler was tight against motherboard ... all wire labels face the top of the case): ...
    (alt.comp.periphs.mainboard.asus)
  • Re: laptop power connectors
    ... It does little to relieve the mechanical stress problem. ... the wire on the solder connections. ... more substantial than hot melt of superglue, but the connections broke anyway. ... The main thing is to take the strain OFF the motherboard and thereby probably halve the likelyhood of a fault occuring anyway. ...
    (comp.sys.laptops)
Loading