Easynote TK85 reboot loop

[Retrocomputer]

Hi!

I'm quite a newbie in motherboard repairing, so please forgive me if I make some mistakes.
As per title, I have a Packard Bell Tk85 (which has almost the same guts as the aspire 5742 or maybe 5733 (at least it surely has the same mobo, a Compal PEW71 LA6285P)
which shows the following symptoms: as I press the power button, the blue lights show up, the fan starts spinning, and it tries to read from the HDD. after a few seconds, it shuts down and reboots. Nothing is ever shown on screen, at any time. No backlight nor any kind of image. If powered on from the battery, it continues to reboot as in a cycle, if powered from supply, it usually reboots one time and afterwards it stays on, with black screen. The fan works fine, the temperature sensing circuit seems to work well, it turns on and off the fan as the temperature floats. Another symptom is that it as I turn it down with the button, after a few secontds it boots up again on its own.
Already stripped to the bare board with just ram, cpu, monitor and power button connected, nothing changes. If booted without any ram nothing changes again, no beeps or anything. What might the fault be on the mobo?
I've already tried testing all the voltage rails, and it seems they're fine.
I just checked the main voltages. They seems to be perfect, imho.
+CPU_CORE: (@C272): 1.03V
+0.75VS (@pin 204 DIMM1): 0.76V
+1.05VS (@L1): 1.05V
+1.05VS_VTT (@PJ12): 1.05V
+1.5V (@pin 5 U24): 1.52V
+1.5VS (@pin 3 U24): 1.52V
+1.8VS (@R944): 1.83V (before and after resistance)
+3VALW (@pin 9 U31 / pin 5 U26): 3.34V
+3V_LAN (@L99): 3.36V
+3VS (@pin 3 U26): 3.35V
+5VALW (@pin 5 U25): 5.03V
+5VS (@pin 3 U25): 5.03V
+VSB (@R935): 18.95V before R, 18.43V after R, 19.18 when switched OFF
+RTCVCC: (@pin 1 D1): 3.05V when ON, 2.75 when OFF

All voltages seem stable, +3VALW, +3v_LAN, +5VALW, +VSB, +RTCVCC are all present with pc is switched off (S5 state).

I've even tried reflashing both BIOS and EC with dumps found on here and on the web, but to no avail. The main BIOS chip is a Winbond W25Q32, the EC chip is a cFeon EN25F10.

Do you have any ideas?

Thank you very much!
Davide

Here's the schematic http://monitor.espec.ws/files/la-6582-r10_165.pdf
Wasn't able to find any boardview, even if it would be of extreme help, since the mobo has next to no silkscreening.

[Retrocomputer]

Re: Easynote TK85 reboot loop

No ideas? If you need anything more, ask.

[Techtiger]

Re: Easynote TK85 reboot loop

Test U16 SIO
Pin 13
Pin 100
Pin 121
Pin 84
PL 10 +VGFX COREP
Did you try with another CPU ?

[Retrocomputer]

Re: Easynote TK85 reboot loop

I was just going do write an update here as I worked for a bit longer on the mobo tonight. I found the probable culprit: by further examining the board, PU12, an ISL62881CHRT has a clear burnt spot on it, and a tiny bit of material ejected onto some tracks underneath. Since it's the voltage regulator for the GPU, it's quite clear why it didn't work!
Do you think it might be useful to try to replace it?
Thank you so much, the absence of +VGFX_COREP lead me on the (maybe) right path!

[Retrocomputer]

Re: Easynote TK85 reboot loop

Ha! Upon even closer inspection it seems that the fault started on pin 12, VIN, as there it was the most damage,it even lifted the trace off the board...

[Techtiger]

Re: Easynote TK85 reboot loop

I was just going do write an update here as I worked for a bit longer on the mobo tonight. I found the probable culprit: by further examining the board, PU12, an ISL62881CHRT has a clear burnt spot on it, and a tiny bit of material ejected onto some tracks underneath. Since it's the voltage regulator for the GPU, it's quite clear why it didn't work!
Do you think it might be useful to try to replace it?
Thank you so much, the absence of +VGFX_COREP lead me on the (maybe) right path!

PU12 ISL62881CHRT Change it if the pad is broken put a jumper from PR263

[Retrocomputer]

Re: Easynote TK85 reboot loop

Hi! Good news here! Today the spare PU12 chip arrived and I soldered it, I needed to make an extremely thin bodge wire to recreate the burnt trace... it was the first time soldering a QFN package, let alone making a trace repair... it's probably not the best but here's my work.
Oh and the laptop turned right on! It seems to be working fine now. Have yet to try with an hdd with an operating system on it.

[Retrocomputer]

Re: Easynote TK85 reboot loop

Hi!
I still have an issue with this laptop.
After that repair, it seems to work fine but after some time (5 to 15 minutes) it shuts itself off. It's not a thermal issue. I've read around it seems it may be something related to ME part. I've already flashed the latest bios from PB website using their own DOS tool. May it be useful to reflash it using a programmer?

Thank you
Davide

[piernov]

Re: Easynote TK85 reboot loop

Dirty ME region will typically cause shutdown after exactly 30 minutes. Not randomly between 5 and 15 minutes. (which sounds more like a thermal or power issue)
If you want to clean ME region, you have to dump the BIOS with external programmer, clean ME in the dump (following win-raid tutorial for example), and flash back the cleaned dump.

[Retrocomputer]

Re: Easynote TK85 reboot loop

Thank you very much! I've worked for a bit this afternoon on the laptop. I flashed another BIOS with a programmer, the equivalent Acer 5733, with PEW71 mobo. It's been working fine ever since, even if I'm facing another strange behaviour: after trying that, I flashed the original PB BIOS/ec, but the acer logo that came with the first flashing remained, and the keyboard fn layout is all screwed. Other than that, the laptop works great.
What can it be?
Thank you.

[piernov]

Re: Easynote TK85 reboot loop

The DMI information are now for the Acer laptop, or the DMI info were empty and set to Acer by default.
Either you have to flash a full dump for Packard Bell using an external programmer (to get the correct DMI info) or you can try to set them manually (if you know what they should be set to) using the DMI tools for Acer.
Can also probably merge the DMI info from the original dump to the new one, but requires more work to figure out what to port over.

[Retrocomputer]

Re: Easynote TK85 reboot loop

That's what I thought, but I flashed the files from PB with an external programmer, wholly erasing thw two chips before every flash...How is it possible that it still thinks it's an Acer?
Thank you so much!

[piernov]

Re: Easynote TK85 reboot loop

Packard Bell and Acer files are the same. Only the DMI info programmed from factory is different.
Typically the default DMI info in the BIOS file show Acer logo.

[Retrocomputer]

Re: Easynote TK85 reboot loop

Thank you again... I still don't understand, though, why files downloaded from PB (that showed the correct logo before as you can see in the picture I attached before) now shows the Acer logo... It wouldn't be an issue actually having another logo, but the fn keys layout is screwed (eg where I have the play/pause icon, it actually turns off/on the touchpad if pressed) Can it be connected in some ways?
Sorry for bothering you
Davide

[piernov]

Re: Easynote TK85 reboot loop

Again, since the original DMI info for that laptop (this specific Packard Bell model) were lost, the BIOS is now using the default parameters which are usually for the Acer-branded laptops.