HP Elitebook 840 G3 keeps rebooting

[Rockton]

I have an HP 840 G3 that will not turn on.
It seems to be stuck in an early boot cycle.
As soon as power cord is plugged in, it starts what seems like a 2 second cycle before it resets and starts it again.
If I hold the power button for 12 seconds. The computer orange light stays on but it become non responsive to the power button and some power rails shut off.

When the resets, some voltages briefly drop.
5.v drops to something like 4.8
3.3 drops to 3.1
12v drops to 11.8. Etc.

I have tried reflashing Bios via USB but it did not work.
Is there two pins i can short on the chip to reset it?

I have disconnected HD, Speakers, Fan, Keyboard even memory and even the power button. The start up boot sequence stays the same.

It looks like 2 orange and 4 orange. But in between the orange flashes, white lights are flashing too.

Anybody have an idea what I should check. ?

Seems to me like something is bring down the 3.3 to GND ( like pressing power button ) as soon as power cable is plugged in and keeps repeating every 2 seconds.

Anybody know where the close lid sensor is?

[Rockton]

Re: HP Elitebook 840 G3 keeps rebooting

An Update

Correction on the voltage drop.
The voltage drops to zero volts every three seconds and the computer resets.
Its stuck in this loop as soon as you plug in the power supply.

[mcplslg123]

Re: HP Elitebook 840 G3 keeps rebooting

Voltage will drop when it resets-that's normal. Question is why it is resetting itself. Start with measuring resistance on all coils. See which rails are coming up within those brief 2-3 seconds. You may need to measure one coil each time it resets due to very short time span. Look carefully for corrosion on mb.

[Rockton]

Re: HP Elitebook 840 G3 keeps rebooting

On Diode test to ground. The coils in red read under 10 OHMS.

As for voltages, I'm getting different voltages depending on what side of the coil I measure.

One time I plugged it in and it didn't start resetting and all the voltages on the board were good. Thought I had it. Next time I plugged it in. Back to the same old reset procedure.