HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

[murko1]

Hello community,
I am hoping that you could help me diagnose and find solution for my problem with HP ZBook 17 G3 T7V35ES.

I will try to describe my problem by posting exactly what I asked on official HP support forum, on reddit, etc.. (basically everywhere I posted, but got zero solution/help).

Original post from 14.12.2020 at HP Support Forum : (link here)

Hello,
I have problem with the HP ZBOOK 17 G3. It suddenly wont fully start, instead it keeps in a power on/power off loop. The loop is:

- power led button blinks quickly 2x and simultaneosly wifi + mute button blinks 1x + complete backlight for keyboard blinks 1x, after that the caps lock lights up for ~2sec -> see video
- front leds: wireless(orange) + power(white) + drive(orange) blink once at same time, then battery led blinks 5x - (changing orange/white) -> see video
- side led is solid white when AC charger connected
- during this process both fans (cpu+gpu) spin up and immediatelly spin down
- this loop is repeating indefitely
- if notebook is on battery, then there is like 1minute delay before the loop begins again, if it is on AC adaptor, the loop repeats immediately (like in video)
- this loop is exactly the same I experienced 2 years ago, but at that time I still had the warranty, under which I sent it to the repair center where they fixed it by, quoting: "Repaired by CMOS reset."
- one common sign, which could cause this loop is in my opinion some shady BIOS update from HP side, because 2 years ago, when the loop begins for the first time, I updated BIOS while the official HP drivers utility marked is as critical (or such), everything was fine for around 2 days, after that the loop started... Fast forward to present time, the same utility suggested again new BIOS (v1.52 I think) and almost exactly after 2 days the dreadfull loop begins again (btw, notebook is in mint condition, as I care about things I use for work, especially when my configuration was almost the highest possible, minus the DreamColor LCD.


So after all, I decided, based on the report from first repair, to reset CMOS by myself per instruction from HP site, I tried:



- unplugged AC adaptor
- removing everything internally connected to MB (internall battery, ssd/hdd drives, RAM sticks, RTC battery, expansion cards, WLAN card, keyboard, etc...)
- drained the residual current by holding power button for 10/30/60sec...
- reseating RTC battery after few minutes/few hours/day..., also bought new RTC battery, which I tried too
- reseating everything piece by piece (to detect probably faulty item)
- tried every suggested key combinations with power button (win + V, win + B, ESC+UP+DOWN), also tried USB BIOS recovery
- tried to run without RTC battery
- tried to run only on AC adaptor, or only on internall battery, or with AC + battery, tried two different original AC adaptors too, also with TB3 dock too


Every steps I made made zero difference, not a single different behavior, still the same loop.
From what I gathered via google-fu, it seems that the service center which made first CMOS reset repair, is not the same as I am trying per suggestion by HP.
The notebook has some kind of NVRAM which is not cleared by suggested steps, thus not fully wiping BIOS settings to default state, which I think is the problem. When the notebook had CMOS cleared by service center, my BIOS password was gone. But from what I learned, the suggested DIY steps wont clear the NVRAM, where the password is stored. So I think, that beside the password, there are more setting stored in that NVRAM, which are causing the loop - thats why all of my efforts are in vain. Also I totally think, that all of the notebook parts are fine, so I hope I wont hear some usuall BS : replace mainboard for 400Euro...


So my final quesiton for the HP officials/service - Can you please reveal how to fully reset CMOS, thus wiping BIOS to default state? I dont care about password, I know it. I just want the **bleep** thing to run again, and not to be ruined by, what I believe **extremely shady** practice by HP with BIOS updates, which will force user to buy unnecesary new mainboard.



Thanks in advance.

-M

Hope you read it all, because I will continue the story - after around 4 months from the time I wrote that original post - the notebook turned on correctly by itself suddenly (I kept the notebook assembled and on battery the whole time without external power supply.[/I] - and it worked finely until today, when the same exact power on/off loop started again ( Note, that I did not perform any BIOS update or changes after the notebook miraculously powered on).

I have backup BIOS created by HP Recovery Tool, I know my password for the BIOS, etc. I just cant figure what is causing this on/off loop and how to prevent it from happening again.

Any insights how to deal with this ?

[mon2]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Hi. Wow..nice and long story.

1) Do you have a multimeter for testing ? Are you capable and comfortable with micro-soldering of electronic parts? Without such skill and tools, this can be difficult. No guarantee that it can be repaired but you can attempt it.

2) Any liquid damage to the unit?

3) Do share the full part # for this laptop. So far, unable to locate any schematics for this box.

Based on your video and experience, believe that your power supplies are power cycling. Just an educated guess at this time but power rails feature current limit protection so that it does not burn out the local components for that rail. Suspecting that some event is causing this issue which is drawing more current than expected by the design team who built this laptop. So it is a bit of a chirp mode of OFF / ON / OFF, etc.

If you have a meter for testing:

Power down and locate where the power adapter enters the laptop. Place your meter in VOLTS mode and measure the voltage on the power adapter at the DCIN connector. This should be likely 18-19V which is common to the laptop industry. The internal logic board then takes this 'high' voltage and steps it down using BUCK convertors. Each buck convertor uses a switching power supply with a honker grey coil if it is for large amounts of current or smaller if lower current for that rail. Respectively, you can measure the voltage on each such coil and post them here.

You may find that some of the grey coils are producing the proper voltage like +12V0 (red lead on coil; black lead on ground)

OR

+5v0

or +3v3

each are expected to be in your system. Then you may find one that is 120mV or something goofy which usually indicates the trouble area of the logic board.

Also look for any parts that may be burnt out / blown up / powder / cracked that is common to damaged logic boards. Take and post clear pix of your logic board for all to review.

If you do not have a meter and soldering equipment then it is highly recommended to seek out a local repair shop with the proper experience to at least test the voltage rails.

There are many good techs worldwide so share where you are located or march on and post your voltage readings and full details of this laptop. Without schematics and boardview files, it will be difficult...

PS: We are a 20 year supplier to HP but for custom h/w we designed for them. From our limited knowledge of their PC group, the laptops are outsourced with varying quality on the construction. It sucks to hear the issues you are facing. Perhaps someone at their customer service line can make some special deal or can influence a proper repair through their channels.

[murko1]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Hi,
I am fine with multimeter measuring, albeit for soldering I havent done it for about 15years since I graduated.

Anyway:

- notebook is in mint condition, never spilled any fluid on it, also properly cleaned from dust every now and then
- serial no: CND6390DSM
- product no: T7V35ES#BCM

EDIT: Semi thorough inspection of the mainboard - I havent noticed any damaged SMDs, but I didnt used any magnifying glass, just by eye inspection.

[murko1]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

I made overall photos of the mainboard, in the case you could point me where to look at and items to measure.
Some arent much clear or zoomed well enough, as I dont have better photo equip atm. I could try to do better shots if you point me at locations you need to see more clearly.

https://imgur.com/a/WDuWwCn

Thanks,
-M

[mon2]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Hi. Received your PM. I think it will be best to review this issue here so many of the experienced techs can offer advice for a repair.

1) The last post (nice photo!) is important as this shows you are dealing with a logic board from Compal (pretty sure) and is p/n LA-C391P. However, so far, unable to locate the schematics for this exact model.

2) You can try a few ideas as follows:

a) remove the CMOS battery off the logic board

b) if this logic board has removable ram - remove the memory stick. Disconnect the hard drive. Wish to work only with the official power adapter.

c) Attach the power adapter and check the voltage (DC mode on your meter; red on the + lead of the adapter connector; black on ground).

What is the reading ?

What may be happening is that you have some cap going stale and is causing an excessive current draw. The local power supply IC will then enter shutdown mode or often will be in chirp mode (cyclic ON / OFF) to prevent damage.

To confirm this, you really need an oscilloscope or a high end multimeter to see the pulsing.

Moving forward, power down and remove the adapter (no battery) and check the resistance on each and every coil on the logic board. Often they are grey in color. Meter in 200 ohms; red probe on the coil + black to ground.

Post each coil reading. If in doubt, post pix of each coil and their value.

We are checking for very low resistance to ground which will denote that you have a bad capacitor onboard that needs to be removed to solve this issue.

[murko1]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

I will do the measuring in a moment, meanwhile I took better photos of the MB:
https://imgur.com/a/8fM857g

[murko1]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

So,
I stripped everything to the bare minimum (only mainboard pcb with gpu/cpu, without ram, without cmos circle battery).

I tested unplugged external power supply, it is allright - 19.35V.
When the power supply cord is plugged, the same voltage is on the most of the expected "points" of SMDs near the input connector (I didnt tested all of them, as there are hundreds of them to test, sadly dont have the steady hand or the time). I looked for points where I could measure some anomalies, but every of them were either around 3/5/19V. Some few were 0.2V.

I measured in a way, that I put black ground tip from multimeter on the ground of the mainboard PCB, then i move with red tip from multimeter on "randomly" choosed SMDs to check them.

[murko1]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Also, it doesnt matter in my case, if i put back RAM, cmos circle battery, or just power the mainboard from battery instead external power supply. The outcome is the same (as described in the beginning).

[mon2]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Ok. Power down and remove the adapter / laptop battery (if connected).

Meter in resistance mode (200 ohms).

Black meter probe on ground.

Red meter lead on each inductor (rather large grey parts with 2 wide metal tabs). These are the heavy current switching inductors and therefore larger than most surface mount components. Also are shielded to prevent interference to nearby radio equipment.

See attached. The pattern on these HP (Compal) logic board appears to be that they are with the "PLxx" (where xx can be any number) for each inductor. You will need to do this for every PLxx inductor.

Write and post the resistance values for each inductor. Again, searching for some very low values to possibly identify a bad cap (often a tantalum) that may be causing this pulsing / post code event.

Followed your post on the video - that LED pattern must mean something to HP. Did you ever find a look up table for these LED (post codes) ? I think that will be a logical start to solving this issue.

[murko1]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Hm, propably identified bad one ? PL37, every other were possible to measure, but not the PL37, for a very very brief moment i saw some value, but not again when tried to measure again.


https://imgur.com/a/PZ79JoQ

PS: PL37 was unmeasurable on any range of Ohm set on multimeter
PS2: Inscription on PL37 :
4R7
612
P62

[murko1]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

I did another round of same measuring, but now with range set to 20M Ohm.
PL8: 0.01
PL39: 0.01
PL40: 0.02
PL37: started at 2, then climbing steadily to around 6, after that it was climbing much slower
PL59:0.12

[murko1]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Measure voltages when powered by external power supply:

PL8: ~1V
PL39: ~3.4V
PL40: ~5.15V
PL59: ~19.5V
PL37: ~0.2V

[mon2]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Home in with a clear picture of PL37 inductor and surroundings. There should be local caps to filter the rail along with mosfets and a local switching power supply IC. We need to review the laser markings on each component to ideally hunt down a typical schematic on how it may be applied by Compal for this design.

Cannot imagine any voltage on this logic board being normal @ ~0V2.

Also believe to have found the blink code sequences for this laptop. Please see attached. Do you see any of these patterns on your box ?

[murko1]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Heya Mon2, thanks for the assistance so far, I will continue tomorrow, as there is around 1am atm and im off already.

[radegoub]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Home in with a clear picture of PL37 inductor and surroundings. There should be local caps to filter the rail along with mosfets and a local switching power supply IC. We need to review the laser markings on each component to ideally hunt down a typical schematic on how it may be applied by Compal for this design.

Cannot imagine any voltage on this logic board being normal @ ~0V2.

Also believe to have found the blink code sequences for this laptop. Please see attached. Do you see any of these patterns on your box ?

I think I found the problem thanks to the picture on the g3 light codes you posted.
Indeed it is the embedded controller which cannot launch the firmware, the first at the top of the list.
Do you think Mon2 there is a way to fix this.

[mon2]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Hi. Personally have not worked with reprogramming the EC devices, yet but others here in the forum have for assorted boxes. From my knowledge, you will need to review the EC part # -> check on which tool can reflash this device -> then apply the specific firmware for this target. Believe that there is an embedded 8051 inside these devices that lose their marbles once in a while. Not clear on this but thought that a bios upgrade can also refresh the EC firmware. Wait on some feedback from @SMDFlea and/or others on this topic.

[radegoub]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

ok i understood, i have to reprogram the ec, it can't be the bq24780s charging chip which does not supply enough current to the ec. i looked everywhere for the firmware of the ec, and i don't found nothing.

[reformatt]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

You need a programmer like a SVOD or Vertaynov. Personally I have the SVOD3.

For ENE/ITE devices, you connect to the keyboard connector and map the data lines from the EC to the SVOD. If you don't have a schematic, you have to buzz these out from the pins of the EC to the connector. Most motherboards have QFP-128 EC's so pins are directly accessible and this is relatively easy. Newer designs though are using BGA EC's and often no schematics are available. As datasheets for EC's are never published, you are pretty much screwed in this respect. Looks like the EC on this board is BGA possibly, hence why no one has dumped it as there is no schematic.

Edit: Not all EC's are programmable. Some load their code from the BIOS chip on start up. Hard to say without knowing what EC this board uses.

[radegoub]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Thanks for the info, I appreciate your help. for the moment I do not have the ec programmer but as soon as I can, I will buy one. As for the chip, it's a nuvoton ncpe586h, the same as in the diagram as the Probook 450 g3.

[athos231]

Re: HP zbook 17 G3 T7V35ES - endless restarting pre-POST loop

Hi,
I have the same motherboard with a burned resistor Q33. It is near the mxm slot. Could you tell me the name because I can not read it.

Thank you in advance