As you say a 5.3 blink code is a system board problem - ''“The embedded controller times out waiting for the BIOS”.''
Try resetting the BIOS by removing the coin cell RTC battery as well as disconnecting the main battery from the system board.
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Here’s a link to the [http://h10032.www1.hp.com/ctg/Manual/c05228250|servcie manual] taken from this [https://support.hp.com/us-en/product/hp-pavilion-15-au100-notebook-pc/12499208/model/12780759/manuals|webpage].
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Here’s a link to the [http://h10032.www1.hp.com/ctg/Manual/c05228250|service manual] taken from this [https://support.hp.com/us-en/product/hp-pavilion-15-au100-notebook-pc/12499208/model/12780759/manuals|webpage].
Use it to gain access to the systemboard so that you can remove the RTC battery. (Note the orientation of the battery before removing it so that you put it back in the correct way). Ensure that the main battery has been disconnected as soon as it can be accessed.
Once the RTC battery and the main battery have both been disconnected do the residual battery discharge procedure i.e. hold Power button for at least 30 seconds to hopefully restore the BIOS to default values.
While the RTC battery is out you may as well test it to ensure that it is still OK. If it isn’t replace it.
Here’s the part number for the battery 741976-001
Once you have replaced the RTC battery, re-assemble the laptop (don’t forget the main battery do it as late as possible to prevent any problems while the laptop is still open), connect the charger and try to turn the laptop on.
Hi @taf
As you say a 5.3 blink code is a system board problem - ''“The embedded controller times out waiting for the BIOS”.''
Try resetting the BIOS by removing the coin cell RTC battery as well as disconnecting the main battery from the system board.
Here’s a link to the [http://h10032.www1.hp.com/ctg/Manual/c05228250|servcie manual] taken from this [https://support.hp.com/us-en/product/hp-pavilion-15-au100-notebook-pc/12499208/model/12780759/manuals|webpage].
Use it to gain access to the systemboard so that you can remove the RTC battery. (Note the orientation of the battery before removing it so that you put it back in the correct way). Ensure that the main battery has been disconnected as soon as it can be accessed.
Once the RTC battery and the main battery have both been disconnected do the residual battery discharge procedure i.e. hold Power button for at least 30 seconds to hopefully restore the BIOS to default values.
While the RTC battery is out you may as well test it to ensure that it is still OK. If it isn’t replace it.
Here’s the part number for the battery 741976-001
Once you have replaced the RTC battery, re-assemble the laptop (don’t forget the main battery do it as late as possible to prevent any problems while the laptop is still open), connect the charger and try to turn the laptop on.