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Possible Solution To Faulty Thermal Sensor

post #1 of 15
Thread Starter 
I posted a thread asking for a solution to my problem yesterday and was not able to get a satisfying answer. i searched the internet for hours and couldn't fnd anything about the faulty thermal sensor problem other than the existence of many similar problems. the only solution seemed to be replacing the motherboard. duh! i know that already, what i wanted wass to fix/bypass the sensor without having to replace the damn board. i couldn't even find a single post staing where exactly the sensor is on the board.
my problem specifically was that beer got spilled on the keyboard. after a while the machine shorted and shut off. I have a Dell Inspiron 9300, with a 1.73 ghz Sonoma CPU. i left the laptop off for two days so some of the liquid would dry out. after some problems and a dozen reboots i got into the bios, then finally through to windows. everything was fine except that the CPU was working at a very low frequency. also the fans were continually at highest speed. the CPU was being reported between 101 mhz to 503 mhz, depending on the software. it was being recognized correctly but showing to operate at 202 mhz in the system properties panel. what was really striking is that the notebook harware software i had installed was reporting the CPU temperature as 85 C. I tried various software to manipulate the CPU frequency to no avail. The temp was a constant 85 C, although i could tell that it was not even close to this temperature since i my laptop was partly disassembled and i could feel the surface of the heatsink with my hand; it was cool.
I finally surmised that the problem was with the thermal sensor on the motherboard. it had probably shorted or got soaked and was reporting the highest temperature it could as a safety measure, thereby limiting the CPU to a very low frequency and not allowing it to throttle above 503 mhz.
My last option, save for replacing the motherboard, was to find the sensor chip, clean it, dry it and hope that it would work again.
But this is not what solved the problem. somewhere on the net i came accross a code, that when entered on an Inspiron 9100 (an older laptop, with a different chipset) would bring up the Thermal Management screen or something like that, which is certainly not accessible via the BIOS. I was playing around with the settings on a program called Hardware sensors monitor, again to no avail, when i finally decided to enter this code: FN key + zxcvasdqwer. almost the second i pressed z, or maybe after x, the high speed fans shut off! after a short while they kicked back into operation but at a low speed, just like they were supposed to. the program hmonitor began reporting a more realistic CPU temp. i tried to play a high-def movie file and finally it played normal, without any lag or stuttering! as i played it, the fans kicked into higher mode, and the temp which had been steadily rising, began to drop. the program, and most other programs were still reporting the cpu at 202 mhz, windows system properties as well. but since it was playing a 720p video file normally, it had to be much higher than that. i did a reboot and voila!!!
all monitoring software are now reporting the CPU at 1.73 ghz. the system temperatures are perfectly normal, and at idle the CPU goes as low as 20 degrees C. The software Speedfan, however, is still giving an error regarding the sensor chip on the motherboard.
I hope this info helps, as I seemed to have fixed the severe thermal sensor problem by a few keystrokes, without having to replace the motherboard or even the sensorchip. in fact, i didn't even have to find the sensor node and clean it.
I came accross more than a dozen people who had a very similar problem to mine, with the temperature being reported at 85-86 C, for no reason. At least those who have a Dell notebok might be able to solve this problem. Good Luck!
post #2 of 15
cool tip

cheers ...
post #3 of 15
unbelievable! I was about to buy a new computer but found your post and it fixed it!

To help others find this solution for the issue I'm going to add some search engine friendly keywords here: fix thermal sensor malfunction, temperature sensor broken, bypass BIOS CPU throttling, disable BIOS CPU stepping, fan constantly on, fan always on, ACPI temperature 85.5C, reset on-chip temperature sensor FN-Z
post #4 of 15
Yeah I was about to say that FN+Z would do the trick. That resets the BIOS fan control. It should be incapable of fixing a dead sensor but I guess it can recalibrate damaged sensor.
post #5 of 15

THANK YOU!!!!!!!!!!

UNBELIEVABLE!!!! You saved my life man, I was going crazy with this crazy fan.. I knew the problem was in the sensor (not in a spyware or dust as 99% of the sites I checked said), and I was almost ready to slice the laptop and live w/out a sensor till I buy a new one (which I could've probably destroyed the whole machine anyway). I registered especially to say thanks. God bless!!!
post #6 of 15
I'm going to move this thread to the Dell home forum, this will definitely be a great tip for that board.
post #7 of 15
So WHEN do you push FN+Z? When its posting and has big DELL logo on the screen?

Quote:
Originally Posted by zzpulp View Post
Yeah I was about to say that FN+Z would do the trick. That resets the BIOS fan control. It should be incapable of fixing a dead sensor but I guess it can recalibrate damaged sensor.
post #8 of 15
Thread Starter 
Quote:
Originally Posted by varan View Post
So WHEN do you push FN+Z? When its posting and has big DELL logo on the screen?
i did it in windows and it immediately took effect
post #9 of 15

Thermal sensor problem fixed !

Your solution saved me!

I had the same problem with my DELL inspiron 9300, and resetting the sensors fixed it all.

Please see this thread

http://www.notebookforums.com/showth...=1#post3130742

In summary, pressing FN+Z did the reset, and all the
thermal sensors and FAN controls in DELL diagnostics passed
with flying colors.

CPU speed and utilization looks great now. CPU speed used
to max out at 220 Mhz, but not it cranks all the way to 1600Mhz.

Thanks a million !
post #10 of 15
Thread Starter 
Quote:
Originally Posted by M.R View Post
Your solution saved me!

I had the same problem with my DELL inspiron 9300, and resetting the sensors fixed it all.

Please see this thread

http://www.notebookforums.com/showth...=1#post3130742

In summary, pressing FN+Z did the reset, and all the
thermal sensors and FAN controls in DELL diagnostics passed
with flying colors.

CPU speed and utilization looks great now. CPU speed used
to max out at 220 Mhz, but not it cranks all the way to 1600Mhz.

Thanks a million !
I read the thread you linked. It p*sses me off that Dell (or any other manufacturer's) technicians are either so incompetent, clueless or totally dishonest as to suggest buying a new motherboard (or, sometimes they will tell you to buy a new laptop outright) when there is an absolutely free, instantaneous and labor-free workaround and permanent solution to this. Talk about bad work ethic (incompetency is included in this). I have ZERO days, hours, minutes of electronics, IT or hardware training; all I had to do was analyze the situation and then seek this information to the best of my abilities. A solution existed and I was able to find it. That simple, really.

So glad that other people with the same problem did not end up forking over $$$ totally unnecessarily.
post #11 of 15
I remember posting something about that a long time ago, stumbling on the fact that fn z turned off my fans for a second.
post #12 of 15
I had similar problem and the following is the detailed symptoms:

- CPU 100% stuck at lower level (600MHz instread of 1.6GHz)
- Dell Dignostic gave fan error 3700:011B, detected speed of 0 instead of 3000rpm
- Bios update, Fan utility, system fix & patch did not solve the problem
- FN + Z method of recalibrating thermal sensor did not work




Fix: There was a faulty joint on the IC (MAX) or Fan connector just below the CPU socket. I reheated each legs of MAX IC and the Fan connector socket by slightly touching them with heated soldering iron. Apply more solder if necessary, but be very cautious not to short any of the connections.

Powered on and the machine runs @ Max speed, fans running and dell dignostic utility passes without problems.


In Summary, fan wasn't running and I thought it was thermal sensor problem. When you get the same error code and the fan does not run, it is likely to have connection issues, since those IC and connector are subjected to frequent heat and cooling cycles.

Hope this helps. I had to write my experience, so that less ppl take their laptop apart completely for a simple fix.
post #13 of 15
Quote:
Originally Posted by aim1nonly View Post
I had similar problem and the following is the detailed symptoms:

- CPU 100% stuck at lower level (600MHz instread of 1.6GHz)
- Dell Dignostic gave fan error 3700:011B, detected speed of 0 instead of 3000rpm
- Bios update, Fan utility, system fix & patch did not solve the problem
- FN + Z method of recalibrating thermal sensor did not work




Fix: There was a faulty joint on the IC (MAX) or Fan connector just below the CPU socket. I reheated each legs of MAX IC and the Fan connector socket by slightly touching them with heated soldering iron. Apply more solder if necessary, but be very cautious not to short any of the connections.

Powered on and the machine runs @ Max speed, fans running and dell dignostic utility passes without problems.


In Summary, fan wasn't running and I thought it was thermal sensor problem. When you get the same error code and the fan does not run, it is likely to have connection issues, since those IC and connector are subjected to frequent heat and cooling cycles.

Hope this helps. I had to write my experience, so that less ppl take their laptop apart completely for a simple fix.
Good sharing!

cheers ...
post #14 of 15

So much agony with my dell 8400 and its cpu-fans abnormal speeding  at startup. And so close to a solution I thought after reading  all good advises here. But unfortunately none of my two Dell keyboards does have an Fn-key!!!!What do I do???? The Fn-key I can find on my vaio laptops keyboard , but not on Dells. What does Fn stands for?

Very thankful for an answer and suggestions for a solution.

Lasse Ekendahl

Stockholm

Sweden

post #15 of 15
Quote:
Originally Posted by trollbacken View Post

So much agony with my dell 8400 and its cpu-fans abnormal speeding  at startup. And so close to a solution I thought after reading  all good advises here. But unfortunately none of my two Dell keyboards does have an Fn-key!!!!What do I do???? The Fn-key I can find on my vaio laptops keyboard , but not on Dells. What does Fn stands for?

Very thankful for an answer and suggestions for a solution.

Lasse Ekendahl

Stockholm

Sweden


Fn (modifier) key is mostly on notebooks. Desktop keyboards normally don't need this Fn key, but you can try the Scroll Lock that could take place of the Fn key on the Dell keyboard. Or get another non-Dell full size keyboard winknudge.gif

cheers ...
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