CPU runs very slow 50% of the time

I have an old Q8400 quad core CPU and often it goes at a fraction of the speed. Rebooting usually makes it go normal speed, for about half a day, then it goes slow again. Novabench scores the CPU at 51 when slow and 381 when fast. The clock is normal, the temperature is normal. Where do I look next? Is it the CPU's fault or the motherboard?

Lamberto Vitali said:

I have an old Q8400 quad core CPU and often it goes at a fraction of the speed. Rebooting usually makes it go normal speed, for about half a day, then it goes slow again. Novabench scores the CPU at 51 when slow and 381 when fast. The clock is normal, the temperature is normal. Where do I look next? Is it the CPU's fault or the motherboard?

Click to expand...

There's two ways I can think of that a CPU would slow down.

1. Throttling due to excessive heat.
2. Control Panel > Power Options... your power plan may have changed, because of an update.
...and 2b. under Advanced Power Settings, your Processor power management settings may have changed.

It could also be a BIOS change, due to BIOS update or glitch.
But rebooting wouldn't fix #2 or the BIOS.

Hardware wise, it may be the motherboard's voltage regulators or even a leaky capacitor.

It almost sounds like Windows is doing it (because rebooting clears the problem).
But I would think it would be the other way around if the cause was Windows.
Like the CPU runs normally, but then all of a sudden... speeds up a lot.


I guess it could be some background process causing the slow down and the reboot stops the process.
Check Task Manager when the slow down occurs.

Ghot said:

There's two ways I can think of that a CPU would slow down.

1. Throttling due to excessive heat.
2. Control Panel > Power Options... your power plan may have changed, because of an update.
...and 2b. under Advanced Power Settings, your Processor power management settings may have changed.

It could also be a BIOS change, due to BIOS update or glitch.
But rebooting wouldn't fix #2 or the BIOS.

Hardware wise, it may be the motherboard's voltage regulators or even a leaky capacitor.

It almost sounds like Windows is doing it (because rebooting clears the problem).
But I would think it would be the other way around if the cause was Windows.
Like the CPU runs normally, but then all of a sudden... speeds up a lot.


I guess it could be some background process causing the slow down and the reboot stops the process.
Check Task Manager when the slow down occurs.

Click to expand...

It's not overheating. I've checked electronically and physically.
Since a reboot fixes it, like you said it's not an option in the control panel causing it, or a BIOS setting. Although, reboot (or complete power down at the mains (and I've disabled hibernation so it's a proper shutdown)) is now no longer fixing it.
I can believe the voltage regulator is off, or a capacitor, it's an old motherboard.

These are the voltages, shouldn't Vcore match the VID it's requesting?
Is 11.3V too low? I notice the same model of PSU powering a Ryzen 9 3900X (much more power draw) is sat at 11.95V, and another of the same model of PSU only powering fans and a couple of SSDs and not a computer as a whole is at 11.6V. I'll try another PSU in it in a week after my holiday (I have some spares of the same model). If that doesn't fix it, I guess I could replace all the capacitors (they don't look broken so I don't know which to change) - do you think it's worth changing just the ones near the CPU?

From HWInfo:
Core VIDs = 1.1V idling, 1.288V under load
Vcore = 0.84V idling, 1.008V under load
VIN1 = 1.472V idling, 1.448V under load
+3.3V = 3.072V idling, 3.056V under load
+5V = 1.452V idling, 1.452V under load
VIN2 = 1.328V idling, 1.328V under load
VIN6 = 0.376V idling, 0.368V under load
3VSB = 3.072V idling, 3.056V under load

Voltages with multimeter = 11.3V (at CPU power connector), 5.3V and 3.35V (at motherboard power connector)

Lamberto Vitali said:

I have an old Q8400 quad core CPU and often it goes at a fraction of the speed. Rebooting usually makes it go normal speed, for about half a day, then it goes slow again. Novabench scores the CPU at 51 when slow and 381 when fast. The clock is normal, the temperature is normal. Where do I look next? Is it the CPU's fault or the motherboard?

Click to expand...

Hi
Would you complete all the details of your PC?
Dave

Based on what you described - could be a faulty capacitor (if not shorted - it can take some time to manifest issues - while overheating). If you can get your hands on a thermal camera - that could really help with spotting the issue (or at least - it's the easiest way to spot the faulty component / or you could touch them by hand individually - and see if any of them gets really hot... the old way of doing things ).

Also, since above CPU is rather old - and you have good temps (proper cooling) - you could try raising the voltage slightly (while testing it for stability on each value increased - ofc). For a newly bought CPU - undervolting used to help more (except for latest generations from Intel - where they sabotaged undevolting / well, they started doing that - even with older versions cause of plundervolt vulnerability - but at least that can be reverted - not like 13th gen and most 12th gen) - but after some time (especially a decade or so) - they can struggle even with default/normal values (a time where increasing the voltage - is the only way to keep it floating till it's not worth it anymore).

davewin11 said:

Hi
Would you complete all the details of your PC?
Dave

Click to expand...

I hadn't done that as I have eight of them! I've filled in the offending one.

neves said:

Based on what you described - could be a faulty capacitor (if not shorted - it can take some time to manifest issues - while overheating). If you can get your hands on a thermal camera - that could really help with spotting the issue (easiest way to spot the faulty component).

Also, since above CPU is rather old - and you have good temps (proper cooling) - you could try raising the voltage slightly (while testing it for stability on each value increased - ofc). For a newly bought CPU - undervolting used to help more (except for latest generations from Intel - where they sabotaged undevolting / well, they started doing that - even with older versions cause of plundervolt vulnerability - but at least that can be reverted - not like 13th gen and most 12th gen) - but after some time (especially a decade or so) - they can struggle even with default/normal values (a time where increasing the voltage - is the only way to keep it floating till it's not worth it anymore).

Click to expand...

I have an IR thermometer, what am I looking for?

I'll also try overvolting after my 1 week holiday, after changing the PSU. That's if the Intel board allows it - if I can't do it in the BIOS, can it be done with software?

I'm referring to this. You can set the min and max, but I don't know what triggers the min or the max.
It could be something like how long the comp has been idle. If so, then a reboot would "reset" that, so to speak.





These are the default settings for my CPU and motherboard in the "Balanced" AMD power plan.
Without knowing "exactly" what triggers the minimum state, I can't know if a reboot would reset that or not.

Lamberto Vitali said:

I have an IR thermometer, what am I looking for?

I'll also try overvolting after my 1 week holiday, after changing the PSU. That's if the Intel board allows it - if I can't do it in the BIOS, can it be done with software?

Click to expand...

Check for shorted capacitors (if shorted - that area gets overheated), then - use a voltmeter to measure the voltage just to be sure. Something like this:


You could try from BIOS - but it can be safer with an app like Intel XTU (official tool from intel) or ThrottleStop (more popular - tho, usually used for undevolting). If the value proves to be faulty in BIOS - you might have to reset it to revert back to default (removing the battery - tends to do the trick with old boards) - while within Windows - it will give you a BSOD and reset (not saving the values). Since your aim is not overclocking - for stability you don't need to increase it that much anyway.

LE.Btw, with TrhottlesStop you can also monitor the CPU usage - even log its activity. If you click on the "Limits" - it will show you if any BIOS options triggered a slowdown of your CPU for whatever reason (be it thermal or power limitation). If nothing gets triggered - that tab is shown as Empty/Black.

Ghot said:

I'm referring to this. You can set the min and max, but I don't know what triggers the min or the max.
It could be something like how long the comp has been idle. If so, then a reboot would "reset" that, so to speak.


View attachment 50708


These are the default settings for my CPU and motherboard in the "Balanced" AMD power plan.
Without knowing "exactly" what triggers the minimum state, I can't know if a reboot would reset that or not.

Click to expand...

Your ussage it's what triggers the low or high. If Windows is idle (or using an app that's almost equally demanding on the CPU) - it will get low, if you use an app that's even moderately demanding - it will raise the frequency. Since your max is set to 100% it can even get in to Turbo Boost mode (dynamic overlooking) - tho, that gets triggered only while using more demanding apps.