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Won't Boot - Back Probed P1 - Voltage Readings

Last response: in Motherboards
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April 2, 2010 3:31:35 AM

I have a P4 Socket 478 that will not boot. I have back probed the P1 connector and the readings are as follows:

Plugged In - Power Supply On - Computer Off

Orange 0
ReD 0
Yellow 0
Blue 0
Purple +4.99
Green +4.98
Grey 0
White 0

Pressing the Power Button on the case gives the following readings
All read Zero Except for:

Purple +4.98 Falls to 0.01 and Returns
Green +4.98 Falls to 0.01 and Returns
Grey +0.08 Returns to Zero

Connecting Green to Ground Starts the power supply, processor fan, hdd's, processor starts to warm with fan removed, and I have occassionally produced 1 long beep with the ram removed using this method, but not consistently. No signs of life on the monitor.

Readings on P1 with Green jumpered to Ground are:

Orange +3.33
ReD + 5.08
Yellow +12.12
Blue -12.29
Purple +4.98
Green 0 - jumpered to ground
Grey +5.16
White -5.18

Can one of you Guru's tell me what all this means ?

Thanx
a b V Motherboard
a b ) Power supply
April 2, 2010 6:01:36 AM

Give the system details, mobo, cpu. etc, wattage of the psu, the voltages seem OK.
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a b V Motherboard
a b ) Power supply
April 2, 2010 6:38:44 PM

If you are watching your 5 volt power line fall to 0 under load and then return it sounds like it's time for a new power supply.
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a c 156 V Motherboard
a c 144 ) Power supply
April 3, 2010 7:28:46 PM

Westom_Fan1 said:

Plugged In - Power Supply On - Computer Off

Orange 0
ReD 0
Yellow 0
Blue 0
Purple +4.99
Green +4.98
Grey 0
White 0

Good values.


Pressing the Power Button on the case gives the following readings
All read Zero Except for:

Purple +4.98 Falls to 0.01 and Returns
Green +4.98 Falls to 0.01 and Returns
Grey +0.08 Returns to Zero
said:
Pressing the Power Button on the case gives the following readings
All read Zero Except for:

Purple +4.98 Falls to 0.01 and Returns
Green +4.98 Falls to 0.01 and Returns
Grey +0.08 Returns to Zero

Bad, probably good, and bad.
The purple wire is the 5 volt standby output. it should alway be at 5 volts. Pressing the case power switch applies a ground to the green wire. This starts the PSU operating. The gray wire is the PowerGood signal. It must go to 5 volts immediately after you press the case power switch. It tells the CPU that all of the outputs are in tolerance and enables the CPU to boot. If it drops back to 0, it will force a hardware reset of the CPU.



Connecting Green to Ground Starts the power supply, processor fan, hdd's, processor starts to warm with fan removed, and I have occassionally produced 1 long beep with the ram removed using this method, but not consistently. No signs of life on the monitor.
said:

Connecting Green to Ground Starts the power supply, processor fan, hdd's, processor starts to warm with fan removed, and I have occassionally produced 1 long beep with the ram removed using this method, but not consistently. No signs of life on the monitor.

Looks like the 12 volt output is present running the fans, drive motors, and the CPU power regulator on the motherboard.



Readings on P1 with Green jumpered to Ground are:

Orange +3.33
ReD + 5.08
Yellow +12.12
Blue -12.29
Purple +4.98
Green 0 - jumpered to ground
Grey +5.16
White -5.18
said:

Readings on P1 with Green jumpered to Ground are:

Orange +3.33
ReD + 5.08
Yellow +12.12
Blue -12.29
Purple +4.98
Green 0 - jumpered to ground
Grey +5.16
White -5.18

If the main power plug of the PSU is connected to the motherboard, there is nothing wrong with these readings (which conflicts with the second group of readings) and the motherboard is probably bad.

If the PSU is disconnected,
it means that either the PSU cannot carry the load and is defective
or something on the motherboard is loading the PSU down and the motherboard is defective.

Suspects, in order, are PSU, motherboard, and (very unlikely) CPU.

Try to borrow a known, good PSU to test your system.

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!