HP poor quality cmos 502 error

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Definitive Diagnosis: Envy x360 Black Screen / CMOS 502 Loop is a Motherboard Defect (RTC Rail Failure)

I am posting this to save others time and money. I am a Cybersecurity Engineer with an A+ certification. I have spent the last week diagnosing an HP Envy x360 (Intel Iris Xe model) suffering from the infamous "Black Screen" boot loop.

The Symptoms:

The laptop refuses to cold boot (Power button LED stays on, screen stays black, Caps Lock light is unresponsive).

The ONLY way to boot is to perform a manual CMOS Reset (Win + V + Power Button), which results in a "CMOS Reset (502)" screen.

Once booted, the system runs perfectly fine until the next shutdown.

Troubleshooting Steps Performed (So you don't have to ask):

Software: Disabled "Fast Startup" in Windows (via powercfg /h off). No change.

Firmware: Verified no pending BIOS updates in Device Manager. Attempted a full BIOS Recovery via Win + B sequence. No change.

Hardware (The Smoking Gun):

Verified the battery model via CLI (wmic path win32_battery).

Replaced the internal battery with a brand new, voltage-matched BN03XL (11.55V) unit.

Result: The exact same behavior persists.

The Technical Root Cause:

These Envy x360 motherboards were designed without a dedicated CR2032 CMOS coin-cell battery. They rely entirely on the main laptop battery rail to maintain the RTC (Real Time Clock) voltage when the system is in an S5 (Soft Off) state.

Since a brand-new battery did not resolve the issue, this confirms a motherboard-level failure. The specific trace or Power Management IC responsible for routing voltage to the BIOS chip when the system is off has failed. The motherboard physically cannot "see" the battery power during a cold state, causing the BIOS to lose its settings and hang on initialization every time power is cut.

The Conclusion:

This is a fatal engineering defect in the board design, likely a blown RTC power rail. Replacing the battery will not fix this. Reinstalling Windows will not fix this.

The Only Workaround:

If you are out of warranty (which you likely are, as this failure seems timed for the 2-year mark), the only way to keep the device usable is to never shut it down.

Change your Power Button and Lid Close settings to Sleep (S3).

Never let the battery drain to 0%.

HP Engineering: Relying on a fragile main rail for RTC without a fail-safe was a critical design error. This device is now effectively e-waste.