HP ProBook 450 G2 stuck in a start loop and without backlight

[kronikus]

Hi,
I bought this one just for DC-jack cable that I needed in this case:
https://www.badcaps.net/forum/showth...067#post846067

Laptop I bought is without ATI graphics chip on board. Just Intel i5.
Laptop is going into loop when power plugged on, regardless of power button but when turned off by holding pwr btn, don't try to start over autimatically - untill pressing button or reconnecting power. Same scenario is when battery is connected. When laptop is turned off by pressing power button, it charge battery without problem and signaling right abuot that. I charged 2 batteries without any problem or unwanted laptop turning-on and loop.

When plugged on, or when power on by button, in about 10 seconds it firstly supply all voltages, start short fan burst and than faint image show on the screen but without any backlight , not even momentarely, regardless of screen position. Than loop became shorter and every 2-3 seconds whole process repeat. Nothing is overheating.

I mesured values only on big coils and results are:
PL303 - 3V; PL302 - 5V; PLM2 - 1.34V; PLZ2 - 1.7V; PLH2 - 2.5V;
PL1501 - 1.47V.

When measuring, screen was detached, nothing was connected except RAM, power, fan and power button.
Before dissasembling, with everything attached, laptop was in the same loop.

Any ideas? For both cases
If needed, I can upload schematics.

TY

[caspian]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

what is displayed in the faint image?
have you converted this laptop to UMA? If so, did it work normally after the conversion?

[kronikus]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

I didn't convert anything but bought laptop "as-is" in hope that has same mobo version and, of course dc cable. Unfortunatelly, I can't see picture now because under any kind of light I use it is not visible. At the daylight, I think I saw white circle with red X inside in the middle of screen, somewhere. Both mobo's are on pictures.

[caspian]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

so you have replaced the ATI chip, right? If so, check if all the GPU voltage rails are present.

[kronikus]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

No, those are 2 entirelly different boards, from 2 different laptops. I didn't touch anything and not replaced or modified anything. Board with ATI chip show only ALW voltages and doesn't turn on any other power lines (as explained on other thread, link is on first post). On other one without ATI, startup-loop is present with faint image and no backlight. I'll try to see if anything is visible on screeen.

[kronikus]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

Schematic for board with ATI...

[caspian]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

measure voltage on PLH2 again. it should be 1.05v.

[kronikus]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

I'm so sorry. It was typo.
PLM2=1.39 fading to 1.37
PLH2=1.05
PLZ2=1.71
PL101=19.75
PL102=2.50
PL1501=1.5
On PQM2 gate voltage keep bouncing between 0.95V and 4.45V and all intermediate values. It's pin 15 on PUM1 (LGATE). Half of the cycle it is on 0.95V and than strat rising an falling.

[caspian]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

It seems powers are all OK. Disconnect the internal screen and test an external one.

[kronikus]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

I just did. No luck there. No picture on VGA, nor on HDMI.

[caspian]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

what other tests did you do so far on this laptop? they may give a clue.

[kronikus]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

I tried BIOS resetting, 3 different RAM modules (different manufacturers and size), both RAM slots. Tried to turn-on without RAM - than fan constantly spin at max speed and without restarting. Part of the board that is always warmer 10 degrees than others are arround 100uF/25V capacitors from B+ to CPU B+ (PCZ7, PCZ8, PLZ1, PUZ2). I'll remove them from board and test separatelly.

[caspian]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

now, make a backup of Bios and try Bios reprogramming using another dump. this is just a try. do not forget making a backup first.

[kronikus]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

I will. In 2-3 days I'll have programmer and try. Thanks.

[kronikus]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

Since BIOS programmer will not arrive any time soon, I did some measuring and maybe find thinghs that can clarify restarting. Again I must emphasize that battery charging works perfectly when mobo is turned off.
I did some measurements on EC during restart cycle.

Present signals (all the time and during restart):
- RSMRST
- SUS_PWR_ACK
- AC_PRES_OUT
- KBC_PWR_ON
- ON/OFF_BTN#
- BATLOW#
- SUS_CLK_KBC stay 1.6V entire time
- KBRST is 0.4V all the time

Resetting signals:
- SIO_SLP_A resetting
- PWR-GD resetting
- SLP_S4 resetting
- SLP_S3 resetting
- PM_PWROK resetting

3VS/5VS resetting but 3VDS/5VDS are present all the time. I suppose that is because SLP_S3# are openning APE8990 which is overcurrent protection (I think), with max current of 6A per channel. And on those channels there are no shorts.

[caspian]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

It is possible that it is not a Bios issue. So you can leave Bios reprogramming to a later time.

[mcplslg123]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

I'll suggest first to fix that dimm display so that you can read message, if any on screen. Check lvds pins voltage.

[dv007]

Re: HP ProBook 450 G2 stuck in a start loop and without backlight

I have the same problem with HP probook 650 g2. Did you figure out what was wrong with it?