MacBook Pro (Retina, 15-inch, Late 2013) - CPU throttling to 800MHz when plugged in to AC

Question

Level 1

10 points

MacBook Pro (Retina, 15-inch, Late 2013) - CPU throttling to 800MHz when plugged in to AC

I have a very bizarre issue at the moment. When I'm using my MacBook on battery power the CPU runs at its usual clock speed of 2.3Ghz and turbos when needed.

For some reason when I'm plugged into AC, I keep noticing the CPU goes down to 800Mhz regardless of load! If I unplug the power the clock speed gradually goes back to normal. This happens a few times a day, it doesn't seem to be anything application specific or a thermal throttling issue as the temps seem fine and the issue doesn't exist when on battery only power.

Things I've tried:

SMC & PRAM reset
Fresh install of Mac OS

Unsurprisingly, when running at 800MHz I get a lot of UI glitches, everything becomes pretty unresponsive to the point it takes about 30 seconds to register a keystroke!

I'm using Intel Power Gadget to monitor the clock speeds.

MacBook Pro with Retina display, macOS High Sierra (10.13.4)

Posted on Jun 21, 2018 4:25 AM

Reply

Answer 1

namboozle Author

Level 1

10 points

Jun 21, 2018 7:28 AM in response to namboozle

So I've done some further debugging/testing.

I've run Geekbench as synthetic workload both on battery and plugged in:

On battery only:

Note the time elapsed and benchmark step

Score:

On AC (charging):

Same conditions, settings etc. Note the time elapsed and CPU frequency drop, limited power consumption and limited utilisation:

Score:

Note the multi-core score being significantly less

Thoughts

It seems to me like there is some kind of power delivery/management issue which is causing the CPU to throttle. I'm going to try another charger and see if I get a similar result.

Reply