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T420 throttling when dedicated graphics are active

T400/410/420 and T500/510/520 series specific matters only
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fleming164
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T420 throttling when dedicated graphics are active

#1 Post by fleming164 » Wed Apr 08, 2015 2:47 pm

I don't know if this has been covered (I can't seem to find anything in search).

I have a T420 with the NVidia GPU but when the GPU is active the CPU throttles itself to 0.80Ghz. the throttling happens immediatly and doesn't revert even when the CPU has cooled down to ~50 degrees. Is this a thermal issue that replacing the thermal place could fix? Or Is this just a feature of the Optimus machines to stop them overheating?
T440s - 1080p i5 12GB 120GB SSD
T420 - i5-2520M 6GB 120GB mSATA
X200 - P8400 6GB 120GB SSD
T61 - T9300 4GB 120GB SSD
SXGA+ T60 - T7200 3GB 64GB SSD
T42/3 - 1.8Ghz 2GB 40GB
UXGA(!) A31p - 2.4Ghz 2GB 100GB SATA (Ultrabay)

dr_st
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Re: T420 throttling when dedicated graphics are active

#2 Post by dr_st » Wed Apr 08, 2015 3:21 pm

This sounds like a firmware/software bug. But to be sure - are you running with a functioning battery? Is the power supply attached? Is it 65W or 90W+
Current: Thinkpad 25 (20K7), Yoga 14 (20FY), X220 4291-4BG, T410 2537-R46, T60 2007-QPG, T42 2373-F7G
Collectibles: T430s (IPS FHD + Classic Keyboard), X32 (IPS Screen)
Retired: X61 7673-V2V, T60 1952-F76, A31p w/ Ultrabay Numpad

fleming164
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Location: Leeds, W. Yorkshire UK

Re: T420 throttling when dedicated graphics are active

#3 Post by fleming164 » Wed Apr 08, 2015 3:50 pm

Never even crossed my mind about whether it was a 65W or 90W adapter! Just swapped to a 90W and it's working fine now!

Thanks!
T440s - 1080p i5 12GB 120GB SSD
T420 - i5-2520M 6GB 120GB mSATA
X200 - P8400 6GB 120GB SSD
T61 - T9300 4GB 120GB SSD
SXGA+ T60 - T7200 3GB 64GB SSD
T42/3 - 1.8Ghz 2GB 40GB
UXGA(!) A31p - 2.4Ghz 2GB 100GB SATA (Ultrabay)

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Re: T420 throttling when dedicated graphics are active

#4 Post by rkawakami » Wed Apr 08, 2015 6:10 pm

Lenovo 20V power adapters have a signal pin inside the barrel (that pointy pin in the center). It's connected to a resistor (or not) so that the laptop can identify what type of power supply is connected. Since your laptop has discrete graphics, it requires the use of the 90W adapter in order to obtain full performance. For some strange reason, the Lenovo engineers chose to have NO resistor mean 90W, which I believe at the time the 20V adapters were introduced, was the highest power adapter available. Using genuine Lenovo adapters should be safe as they will self-identify and the Thinkpad will adjust accordingly.

If an aftermarket adapter does not follow this resistor standard, in other words, if it has none, it may be considered by the laptop as a 90W unit, even if it's actually rated lower. If the adapter is actually 65W but the laptop thinks it's using a 90W, that can lead to overstressing the adapter.
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dr_st
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Re: T420 throttling when dedicated graphics are active

#5 Post by dr_st » Thu Apr 09, 2015 2:00 am

rkawakami wrote:If an aftermarket adapter does not follow this resistor standard, in other words, if it has none, it may be considered by the laptop as a 90W unit, even if it's actually rated lower.
Yep, that's exactly how some of those fake 65W are. :)
Current: Thinkpad 25 (20K7), Yoga 14 (20FY), X220 4291-4BG, T410 2537-R46, T60 2007-QPG, T42 2373-F7G
Collectibles: T430s (IPS FHD + Classic Keyboard), X32 (IPS Screen)
Retired: X61 7673-V2V, T60 1952-F76, A31p w/ Ultrabay Numpad

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