ASUS GA401QM No POST (RAM issue?)

[ResoluteHawk]

I have yet another ASUS GA401QM but this one is not POSTing. It does turn on and all system voltages are present, however I am not getting an image on the screen nor on an external display. I've tried swapping in a known working BIOS chip and no luck.

I measured voltages and resistances around the board and I noticed that when the system is turned on, the CPU VCORE voltage is 1.098V when it should be just a little bit higher at 1.4V (on a working system). The other thing I noticed is that my 1.2V rail for the memory is 98 Ohms to Ground when it should be around 250 Ohms (again, on a working system). I want to be 100% sure that my onboard RAM is partially shorted before I start removing the onboard memory chips and resoldering known good ones on.

What I need to know here is how can I disable the onboard RAM? I'm looking in the schematic and it says to disable the LPDDR4x (what I assume is the onboard memory), I need to have "DDR4 enabled and connect a pull-down resistor or direct connect to VSS". I'm not sure what this means but I assume that it means shifting the 0 Ohm resistor on VDDIO_MEM_FB_H (PR8610) to VDDIO_MEM_FB_L (PR8615) to disable the onboard RAM. Then to enable the DDR4 memory controller, it states that there needs to be a 0 Ohm resistor connected to VDDIO_MEM_S3.

This would mean that if I move that PR8610 to PR8615, both of these statements are logically 0 instead of 1 according to the schematic. I don't know if moving this resistor disables the memory completely or just one of them (onboard vs slotted).

This confuses me because the schematic states that either the M_DDR4 strap or M_LPDDR4 strap must be pulled up, but never both. Is there another resistor that I have to move? If so, where in the schematic is this noted?

UPDATE: What I didn't consider is that maybe the DDR4 socket gets pulled from High to Low depending on if RAM is installed in the socket. By default, it's Low because no RAM is installed. But the memory on the board is always High because you can't just swap the onboard memory out, hence you have to pull the onboard memory to Low by moving that resistor.

I'm most likely wrong with everything in this post so that's why I need help.

I'm using 2 schematics that use the same graphic for the memory signal descriptions because the GA401QM one is very blurry.

Schematic and Boardviews:
GA401IV (clearly legible memory signal tables):
POST #4
https://www.badcaps.net/forum/showthread.php?t=115717

GA401QM (my board): https://www.badcaps.net/forum/showthread.php?p=1246796

[ResoluteHawk]

Re: ASUS GA401QM No POST (RAM issue?)

Ok so I completely missed the fact that the memory on the board was Samsung memory and comparing my resistance to ground measurements to a working board, they are both about 98 Ohms. This more than likely means that the memory on this board is not the issue preventing POST.

I still was not able to find anything about the strap configuration to disable the onboard RAM but since the resistance matches a working board, I think I can move on from this idea.

[mcplslg123]

Re: ASUS GA401QM No POST (RAM issue?)

DRAMRST# present? All_SYS_PWRGD status?

[Sephir0th]

Re: ASUS GA401QM No POST (RAM issue?)

I do agree, 98 Ohms sounds far aways from a issue regardless the manufacturer. One of the modules still could have failed in another way, though.

But you did not mentioned the state of the GPU at all. Whether a) is is full powered and b) Whether resistance are in expected ranges

[ResoluteHawk]

Re: ASUS GA401QM No POST (RAM issue?)

DRAMRST# present? All_SYS_PWRGD status?

I don't know where to check for DRAMRST#, but All_SYS_PWRGD is present (3.3V).

Whether GPU is: a) is is full powered and b) Whether resistance are in expected ranges

GPU appears to have the power it needs at boot except for the video memory.

On a working system that I have:
a) The voltage on GPU VRAM starts at 1.253V then drops, then goes up to 1.4V.
b) CPU VCORE starts off at 1.4V until it gets out of the BIOS and into Windows.

On this system:
Coils for GPU VCORE are at 0.75V, 1.8V rail is present (~600 Ohms), 1.2V on the VRAM coils is present when powered on, and resistance for the GPU Memory is right around 30 Ohms (Samsung VRAM).

CPU VCORE coils measure 3 Ohms, and the one on the top right measures 7.2 Ohms.

[Sephir0th]

Re: ASUS GA401QM No POST (RAM issue?)

I don't understand what you're doing in the CPU VRM when you're dealing with missing VMEM tbh.

You need to find out what is wrong there

[ResoluteHawk]

Re: ASUS GA401QM No POST (RAM issue?)

Memory voltage is present. We're not missing VMEM unless I'm not understanding you. I don't know where to check for DRAMRST#.

The problem is that we have 1.2V on both PL9401 and PL9402. The GPU memory is not being pulled High like it states in the schematic. It's staying Low at 1.2V. I'll have to check the resistors for MEM_VDD_CTL.

CPU is receiving voltage but it's supposed to be higher before being able to POST (+VCCGT needs to be present for integrated graphics, or for a display in this case). This is why I'm measuring CPU VCORE. I need to know what is happening with all system voltages.

If the CPU is receiving power, we know in terms of the power sequence that (ALL_SYSTEM_PWRGD)VCCST_PWRGD_CPU(CPU) is present at the least.

I will have to test the remaining 9 items of the power sequence when I get home. The problem lies between (ALL_SYSTEM_PWRGD)VCCST_PWRGD_CPU(CPU) and +VCCGT

[Sephir0th]

Re: ASUS GA401QM No POST (RAM issue?)

Oh I see. Missed the part with the 1.2V present. If BIOS was ruled out already per 100% then I'd continue with a detailed visual inspection of the motherboard.

History of the device might give the key clue in these cases.

[ResoluteHawk]

Re: ASUS GA401QM No POST (RAM issue?)

Ok so I'm still a little hairy on where the remainder of these signals are located.

I found DRAMRST# on Pin 108 of the SODIMM slot. No voltage on it.
No voltage on PLTRST# at R0704.
The only point I can find for PM_PWROK_PCH is GC6FBEN_PCH. No voltage.
I did look at APU_PWRGD and APU_RST# and those are both 1.8V.
SYSRESET# is 3.362V.

So the signals seem to stop at PM_PWROK_PCH if I measured correctly.

This was a laptop that I purchased to repair and I can still return it. When I first received it, it was ticking when plugged in and powered on. I found that the ticking was was coming through 3 places: the CPU, the EC, and the BQ24800 chip.

I found that voltage was alternating at the gate of PQH8901, so I removed the BQ chip and replaced it. The ticking is gone and voltage no longer alternates at the gate of PQH8901 and the battery actually charges when plugged in now.

This leads to where we are now.

[Sephir0th]

Re: ASUS GA401QM No POST (RAM issue?)

The schematics describes a AMD platform, so no PCH related signals and the included power sequence diagram will be almost useless for this reason.

The APU VRM seems to assert even two different PGood Sognals. APU_PWRGD and CORE_PWRGD. Measured both of them?

[ResoluteHawk]

Re: ASUS GA401QM No POST (RAM issue?)

Yes both signals have voltage present.

APU_PWRGD is 1.8V
CORE_PWRGD is 3.342V

[Sephir0th]

Re: ASUS GA401QM No POST (RAM issue?)

It has this weird SL4GE42553VTR present which has failed at one of the systems on my bench once. With any luck you'll find a (partial) short to GND at either one of the BUF_PLT_RST# or M_B_RESET#. But if nothing turns out and visual inspection already done, rabbit hole.

[ResoluteHawk]

Re: ASUS GA401QM No POST (RAM issue?)

Hmm. I didn't find that chip but I did measure those two signals in diode mode before and neither signal is shorted to ground.

Yeah....seems like this one is indeed a rabbit hole.

So why put PCH signals in the schematic if this is an AMD board and there is no PCH?