Dell G15 Ryzen Edition (LA-K454P) – No SPI Activity, No Boot, No startup

[Raven7032]

Hello everyone!
Stucked with this problem.
Model: Dell G15 Ryzen Edition
Board: GDL LA-K454P
Symptoms:

• Board powers on (consumption ~0.5A), but no boot or display.
• Fans spin briefly, keyboard backlight turns on, then fans stop.
• Can be shut down via power button (EC active).
• No POST, no BIOS splash, no backlight.
• Led is blinking 2 orange 1 white
• No activity on SPI bus (no CS#, no CLK, no MOSI/MISO) even after pressing power.
• No APU_PCIE_RST# - 0V

Measurements:

• All voltage rails present: +1.8V, +0.75V, +3VS, +5VS, VDDCR_VDD, VDDCR_SOC, DDR VDDQ, VTT.
• EC_RSMRST# = 1.8V, SLP_S3#/S5# = 3.3V, APU_PWROK = 1.8V, APU_RST# = 1.8V
• DDR_A_RST# and APU_PCIE_RST# remain LOW (not deasserted).
• Checked SPI_CLK, CS#, MISO, MOSI on BIOS chip – no real activity.
• Reflashed BIOS with clean Dell BIOS Region (1.23.0) via external programmer.
• After CPU replacement nothing changed.

+3VS 3,4V
1.8VS 1,8V
0.75VS 0,75V
VDDCR_VDD 0,8V
VDDCR_SOC 0,8V
SYS_PWRGD_EC 3,3V
APU_RST# 2,1V
APU_PWROK 1,8V
C_RSMRST# 1.8V
13) SLP_S5# 3.3V
(14) SLP_S3# 3.3V
(15) SYSON 3.3V
(16) SUSP# 3.3V
(16) +1.2V_DDR 1.2V
(16) +1.2V_DDR
(17) +3VS 3.3V
(17) +3VS_APU 3.3V
(17) +1.8VS 1.8V
(19) +0.75VS 0.75V
(20) VGATE 3.4V
(20) +VDDCR_VDD 1V
(20) +VDDCR_SOC 1V
(21) SYS_PWRGD_EC 3.3V
(22) APU_PWROK 1.8V
(22) APU_RST# 1.8V

What I can check more? Seems CPU is not starting, but cant find reason why =(

[Raven7032]

Revived the laptop.
Initially, the diagnostics pointed to a dead CPU, so I replaced it with a new one from AliExpress.
However, I made a mistake here—I should have measured the voltages directly on the CPU, not just on the chokes. It turned out that while the 0.75V power was present, it wasn't complete. On Ryzen, there are two power rails: +0.75V VDDP and +0.75V VDDP_S5, and one of them was missing. While measuring the resistance on these lines between the CPU and the choke (PL7506), I found a short circuit (1.2 ohms). I thought the solder balls might have bridged, so I removed the CPU and measured the resistance separately on the CPU and the board (on choke PL7506). Both showed normal resistance. After reseating the CPU, the short circuit reappeared!

At this point, I started tracing where the power was coming from and began checking the PWM controller (PUV03) circuitry. That's when I found this nasty homemade jumper between resistors PR7519 and PR7525 (connecting GND and FB_0.75V_S5).
I removed the jumper, and the CPU powered up, but the board's diagnostic LED started flashing different error codes randomly:

• 2-7 Display failure - SBIOS message
• 2-6 System board or chipset error
• 1-7 Non‑RPMC Flash on Boot Guard fused system

The display error appeared only a couple of times, and the last white flash was incomplete.
I tried different BIOS versions. With the wrong BIOS, error code 2-1 (CPU failure) appeared.
When I removed the RAM, a memory error popped up, which indirectly indicates that DRAM initialization passed. Also, APU_PCIE_RST# was at 3.3V, meaning the main initialization completed, and the issue was elsewhere.

Eventually, I ignored the error codes and kept digging. I discovered that while all the power rails for the display were present, the panel wasn't responding with CPU_EDP_HPD. I bought a broken but functional display, connected it, and the laptop came to life—an image appeared. Now I need to check further for GPU and other peripheral issues.

[Raven7032]

Overall, the CPU turned out not to be the culprit. It really didn’t start, but for a completely different reason. One of the voltage rails (0.75V) was missing. It was absent because of a jumper between resistors PR7519 and PR7525 (GND and FB_0.75V_S5). Someone had placed it there, and it definitely wasn’t me.

Now, it’s blinking 1 yellow and 7 white.
"Non-RPMC Flash on Boot Guard fused system."
But Ryzen doesn’t even have Boot Guard.
"BIOS integrity failure or PSP-based validation failed."

UPD.
I flashed the BIOS to the one I dumped when the laptop first came into my hands.
Now it’s blinking 2 yellow and 6 white.
"System board/Chipset Error."

What could this even be?

[Raven7032]

Revived the laptop.
Initially, the diagnostics pointed to a dead CPU, so I replaced it with a new one from AliExpress.
However, I made a mistake here—I should have measured the voltages directly on the CPU, not just on the chokes. It turned out that while the 0.75V power was present, it wasn't complete. On Ryzen, there are two power rails: +0.75V VDDP and +0.75V VDDP_S5, and one of them was missing. While measuring the resistance on these lines between the CPU and the choke (PL7506), I found a short circuit (1.2 ohms). I thought the solder balls might have bridged, so I removed the CPU and measured the resistance separately on the CPU and the board (on choke PL7506). Both showed normal resistance. After reseating the CPU, the short circuit reappeared!

At this point, I started tracing where the power was coming from and began checking the PWM controller (PUV03) circuitry. That's when I found this nasty homemade jumper between resistors PR7519 and PR7525 (connecting GND and FB_0.75V_S5).
I removed the jumper, and the CPU powered up, but the board's diagnostic LED started flashing different error codes randomly:

• 2-7 Display failure - SBIOS message
• 2-6 System board or chipset error
• 1-7 Non‑RPMC Flash on Boot Guard fused system

The display error appeared only a couple of times, and the last white flash was incomplete.
I tried different BIOS versions. With the wrong BIOS, error code 2-1 (CPU failure) appeared.
When I removed the RAM, a memory error popped up, which indirectly indicates that DRAM initialization passed. Also, APU_PCIE_RST# was at 3.3V, meaning the main initialization completed, and the issue was elsewhere.

Eventually, I ignored the error codes and kept digging. I discovered that while all the power rails for the display were present, the panel wasn't responding with CPU_EDP_HPD. I bought a broken but functional display, connected it, and the laptop came to life—an image appeared. Now I need to check further for GPU and other peripheral issues.