T60 - GPU temp rises when using external monitor via DVI?

[dr_st]

My T60 w/ ATI X1400 spends most of its time docked, and connected to an external monitor via DVI.

Recently I noticed a peculiar thing. If the machine has been running with the external monitor off, and I turn it back on, the GPU temperature (according to TPFanControl) immediately jumps by anywhere from 3 to 9 degrees centigrade, with the average being about 6 degrees.

Turn the external monitor off - and it goes back down.

I've investigated it further and it seems that just using an external monitor via the DVI on the dock causes this several degrees difference in the reported GPU temperature. It doesn't matter if the DVI monitor is used as a single monitor or together with the internal LCD. However, using the external monitor via the VGA on the dock does not change the GPU temperature.

So what is it? A sensor glitch? Some special circuitry activated for DVI that for whatever reason causes GPU temperature to increase? Some driver setting activated only for DVI mode?

I wonder if anyone else has experienced similar behavior.

[Binh]

AFAIK, it is related to PowerPlay mode of ATI graphics. One of drawbacks of ATI PowerPlay comparing to NVidia PowerMizer is that when you connect an external monitor, PowerPlay is always disabled. Please, check GPU frequency with connected and disconnected external monitor.

[dr_st]

You know - I've just looked into it and now I am even more confused!

You are 100% right about PowerPlay being automatically turned off (even if enabled) when an external monitor is connected (verified by looking at frequencies and running benchmarks).

However, this does not explain why there is no temperature increase when the external monitor is connected via VGA (even though the PowerPlay feature is being turned off, which I verified).

Furthermore, after I went and disabled PowerPlay completely - nothing changed. The reported GPU temperatures are still on average 6-7 degrees higher when a DVI monitor is enabled compared to when it is disabled (matters not if an external VGA monitor is used, or if it's just the internal LCD).

I dug through all the settings I saw in the CCC, and could not find a single thing that was configured differently for VGA mode and for DVI mode.

Still looking for the culprit...

[Binh]

Yesterday I made a quick test on my T60p. The GPU temperature is actually raised by 3-5 deg when switch from laptop screen to DVI output. Possible explanation is that the DVI transmitter is a separate block and it requires more power than VGA DAC converter.
Did not have time to test power consumption though.