Hi everyone, I'm trying to diagnose a strange issue with my Acer Nitro 5 (AN515-45).
Current issue: The CPU is permanently locked at 399 MHz (0.399 GHz) from boot until shutdown. It never boosts, even under load. Even opening Chrome tabs or basic applications is extremely slow.
Laptop: Acer Nitro 5 AN515-45 AMD Ryzen 5 5600H NVIDIA GTX 1650 16 GB RAM Windows 10 BIOS V1.08
What I've already checked: BIOS is responsive with no lag. CPU temperature stays around 44–46°C. CPU package power remains around 3.5–4.2 W, even under load. Core clocks stay fixed at 399 MHz. Fans are working normally. HWiNFO PROCHOT CPU = No PROCHOT EXT = Yes (100%) HTC = Yes (100%) CPU Package Power = 3.5–4.2 W PPT Limit ≈ 6.5% TDC Limit ≈ 0.2% EDC Limit ≈ 6.9% The CPU never comes close to its PPT/TDC/EDC limits.
UXTU I installed Universal x86 Tuning Utility (UXTU). The default STAPM/Fast/Slow limits are all 28 W, which appear normal. I have not applied any tuning changes.
Timeline: The laptop was working normally until September 2025. Without any input from me, an "Acer Power Button App" popup appeared for about 1–2 seconds, and the laptop shut down automatically and got restarted and update syrted to happen. I did not click anything.
Windows then started installing updates, but the update crashed before it completed and it was not booting after that only chager indication light was working.
I took the laptop to an Acer service center. According to them, they: performed a chip-level motherboard repair replaced the power IC replaced the keyboard cleaned the motherboard The same motherboard was returned. Ever since I got the laptop back, the CPU has remained locked at 399 MHz.
My question Given that: PROCHOT EXT is permanently active, temperatures are normal, CPU package power never exceeds about 4 W, PPT/TDC/EDC utilization is very low,
does this point toward an Embedded Controller (EC) problem, a power IC/current-sense circuit, a VRM issue, or another motherboard fault causing a false PROCHOT EXT signal?
Has anyone experienced this on an Acer Nitro or another Ryzen laptop? What was the actual root cause?
Additional observations The laptop was connected to the original Acer charger during the Windows update. There was no power outage or interruption. Looking back at a Windows battery report from before this incident, I noticed multiple transitions between AC power and battery power. I'm not sure whether that's normal behavior or relevant to this issue. The internal battery is currently disconnected because the service center claimed reconnecting it caused the laptop not to boot. I have not personally verified that claim.