Laptop i5-6300HQ CPU suddenly underclocking, stuck at 0.78 GHz

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boreal187

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Feb 15, 2017
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Hello,

My Dell XPS 15 (Core i5-6300HQ) started behaving strangely a couple of days ago, the performance in gaming suddenly dropped to a fraction of what it used to be. I tried all kinds of things, including formatting the whole PC but to no avail.

I can now finally narrow it down to the CPU performance, which seems to be stuck at 0.78 GHz, regardless of whether I'm on battery or plugged in, regardless of what software I am running (even during gaming). My power plan is on High Performance so I can't see why it would only run at that frequency, when the processor is capable of up to 3.2 GHz.

I tried even resetting the BIOS and re updating all drivers but nothing's changed.

Any suggestions?

Many thanks.
 

boreal187

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Feb 15, 2017
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Thank you. I can't quite tell where on CPU-Z I can see the temperature, but the laptop is completely silent and not at all warm to the touch, for those few minutes when I am testing a game and the CPU is constantly stuck at 0.78 GHz
 

boreal187

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Feb 15, 2017
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I found online some other users having a similar issue and using this software called ThrottleStop, that lets you disable something called BD PROCHOT. This does work for me too, but only while the software is running, so I am thinking it's not probably a permanent solution...
 

boreal187

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These are the temps at Idle


And these when running a game in the background
 

unclewebb

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BD PROCHOT stands for bi-directional processor hot. It is basically a signal line going to your Intel CPU. When a CPU receives a signal on this line, it is forced to immediately start throttling. It does this by dropping the CPU multiplier down to 8 so your CPU will be stuck at about 800 MHz which is exactly what is happening to you.

This problem is rarely caused by anything over heating. It is almost always due to a bad sensor on your motherboard or your power supply that has gone bad. It could be a temperature sensor that is bad or it might be a sensor on your motherboard voltage regulator. The engineers that designed your laptop would know exactly what sensor has failed but trying to explain this subject to someone at a call center will be like you are talking a foreign language to them. They will probably tell you to re-install Windows but this is not going to fix a sensor that has failed.

The only way to fix this problem is to start swapping parts. If a new power supply does not fix this then the motherboard will need to be swapped out. The sad part is that if this does fix this problem, the same thing might happen a month or 6 months from now. Trying to get this permanently fixed can become a big headache. It is far easier to run ThrottleStop and disable BD PROCHOT. This blocks external throttling signals from reaching the CPU so it can run at its full Intel rated speed. If your CPU ever gets too hot, it will still be able to throttle whether BD PROCHOT is enabled or disabled. Internal throttling signals will still be heard by the CPU. Only the external throttling signals will be blocked.
 

boreal187

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Feb 15, 2017
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Thanks UncleWeb. I've actually started getting used to using your ThrottleStop software, it's a great piece of kit :)

Exactly as you imagined, I tried explaining this problem to the Dell customer support, and it wasn't making any sense to them at all. They recommended to run a Dell diagnostic tool to check the integrity of all the components of the laptop, which all passed; then they recommended to update drivers and BIOS... And I did myself a Windows factory restore, to no avail.

I have been advised to try open the lid of the laptop to check for accumulations of dust, which I'll try.... But like you said, it all points to a bad sensor somewhere. If it was a bad power lead, then it would work fine when on battery, wouldn't it? But it has the same behaviour.

I supposed I'll just continue using ThrottleStop for the time being. It works really well and gives me really great control over the power of my CPU. Thanks for making this great software available for free :) I've asked you a few usage questions on the NotebookCheck forum...

Thanks again for your comments. From the research I have been doing on this, it seems your diagnosis is spot on.

 

boreal187

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Feb 15, 2017
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The solution to this issue was to just remove the battery. Some other users around the web experienced this on the XPS, removing the battery and putting it back in seems to have stopped the issue. The fans were also very dusty so that might have been another cause...
 

kameyo

Commendable
Sep 7, 2016
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@unclewebb thank you... I almost bought a new MB and CPU because of this BDPROCHOT... You are a beautiful person.
 

boreal187

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Feb 15, 2017
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While ThrottleStop does help with the issue, for me the removing and re inserting of the battery and cleaning the dusted up fans made the issue stop
 
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