I guess I was barking up the wrong tree in the previous post. I’ve learnt that S1 sleep is indeed supposed to leave the CPU and the fans on. I was most likely using S3 on my previous HTPC, not S1 as I initially thought. I thought it must have been S1 since S3 takes so long to resume from on the new HTPC. But the error is not always where you are looking.

As i mentioned i also have a problem with the power supply. The symptom is that it takes several attempts to start the computer. But on one lucky occasion it started on the first attempt. At that particular occasion it only took a few seconds to get back to the login screen from S3 (as opposed to over a minute in most cases). So potentially it wakes up as fast as my old HTPC, just not everytime.

My hypothesis is thus as follows: The failed start attempts corrupt the state in the memory which makes the computer revert to the state stored on HD (I think one of the features of S3 is that it stores the state both on the HD and in the memory). Resuming from HD is more time consuming than resuming from memory obviously.

So what initially looked like two different problems was probably only one. Still waiting for that new PSU…