General » Dell fan control » Dell Inspiron 8200
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Dell Inspiron 8200
Post by lysdexic on Feb 27, 2007, 8:38am
Hi everyone,
This post is all about the Inspiron 8200 - it may be relevent to other Dell lappy's - if you experience the exact same symptoms as I do, chances are it does.
The laptop is a Dell Inspiron 8200.
2GHz Pentium 4 M(obile) CPU
1GB RAM
Ati Radeon M9000 Graphic Card
1600x1200 Dell Ultra-Sharp screen
CD/DVD combo
40 GB hard Drive
Running XP Pro SP2
I have used this machine to play Half-Life 2 (which it does with most of the settings at the high position).
For work, I can easily run 3DS Max 9 (which is great to work with on the gorgeous hi-res screen) - and it renders at an acceptable speed too.
Everything was fine and dandy until a few weeks ago.
For some odd reason, the machine began to slow down and the fans kicked in at full tilt.
My first thought was - there must be a heating problem. (odd, because the machine didn't seem to be excessively hot)
I thoroughly cleaned the heatsink and fan area - no difference.
I bought an Akasa cooling unit (this is really just a flat metal plinth with fans built in. You sit the lappy on top of this and it provides extra cooling). - no difference.
I started to delve into the CMOS setup and tried a number of different setting in the hope of over-riding the built in thermal controls. - no difference.
I was running out of ideas by now, so I started to trawl through a stack of posts from all over the net concerning this very same problem. - here is what I found out.
The Inspiron 8200 (and possibly some of the other 8*** series) have a potentially faulty thermistor built into the motherboard. Most users have a trouble-free experience with their 8200 for about 3 years, then one day, the lappy starts to slow down and its all down hill from there onwards. - this is exactly what has happened to my machine.
Three years is a long time for a built-in fault to appear, so I guess I can't complain to Dell for this - they probably didn't see this one coming, however, the only solution they have for fixing the problem is to replace the motherboard (yeah, right 
).
As most people will know, the P4 Mobile processor has this d**n speed-step technology built in. Essentially, what this does is slow the CPU down when it starts to overheat, therefore avoiding damage. It also gets involved in power management, especially when on battery power since a slower CPU consumes less power, thereby conserving the battery and also reducing heat. The thermistor is the trigger for the switch to low or high speed. It also plays a part in the way the fans kick in to get rid of the heat.
The faulty thermistor can switch to the lower CPU state with ease, in fact it does it far too early. This would not be a problem if it would also switch back to the higher CPU speed, - BUT IT DOESN'T. Instead, your lappy sits there working at a snail's pace, no matter how cool it is.
Incidently, I discovered from a few posts on the net that you can manually switch the CPU back to its faster state by pressing the fn +Z key combination. This makes things instantly speed up, but the thermistor will soon kick it back down again. Pressing fn +Z over and over starts to get tedious after 5 minutes 
Replacing the motherboard is not a realistic option. Dell won't (or can't) give details of where the thermistor is on the board - this probably couldn't be fixed without damaging the board anyway, so I was thinking my trusty 8200 was about to be retired.
After battling with this problem for the best part of a month, I noticed that the slow-down happened when the fans kicked in at a fast speed. On the rare occasions that they ran at a slow speed, the CPU still ran at full speed.
What does this mean? Well I guess the faulty thermistor is kicking in at a temperature way lower than it should. I also think it turns the fans on to a fast setting when this happens. It seems to be unable to switch back to the higher CPU speed, regardless of how cool the system is running - and it doesn't switch off the fans either.
I have a strong suspicion that the fan speed has something to do with the way the thermistor screws up. Maybe another sensor is providing feedback to the thermistor (ie a fan speed controller). If this were the case, the thermistor might not switch back to the higher CPU speed if its being told the fans are running at max speed (suggesting the system needs to be cooled, so stay in the lower CPU mode and keep those fans running full-speed).
To test the theory, I installed this wonderfull fan controller (current version V3.1).
I set the parameters to run both the fans at a slow speed and kicked them in at a low temperature of 35 degrees C. I was hoping I could keep the system cool enough to avoid the thermistor kicking in - hence the CPU would always be working flat out.
I'm happy to report that after 48 hours of continuous use, the CPU temperature has never gone beyond 55 degree's C and the speed has never dropped from its 2GHz fast setting.
I'll continue to tweak the settings and see how high the CPU temperature can get before the thermistor spoils the party, but for now, I've got a working machine again.
So, my eternal thanks to Mr Diefer and his amazing program - he has saved my wee lappy from certain death 
- I'll send a little present via PayPal when I get home at the week end 
Sorry about the long post - I hope this info is of use to someone out there.
Re: Dell Inspiron 8200
Post by hawker on Feb 27, 2007, 12:46pm
Interesting.
What I suspect is that something is causing a non linear response from the thermistor.
A Thermistor is simply a resistor whose resistance varies based on temperature. My guess is that it is cracked or some such and once the temperature reaches a certain point the expansion/contraction changes the value (either up or down depending on if it is a PTC or NTC type thermistor).
There is no feedback on a thermistor as you imply - it is simply a resistance so I suspect that there is some temperature threshold that screws it up, not fan feed back as you imply.
It most likely is a small surface mount device with 2 to 3 legs (SOT-23 or some such) so if you can find it on the PCB it should be fairly easy to change. It is probably stuck to a heat sink or something like that so you should be able to find it yourself pretty easy.
Replacements of similar values would be here
http://www.digikey.com/scripts/DkSearch/....US&Cat=34407603
Good luck.
I have an I8200 as well. My issue is my fan bearings are going out. I got a new fan but have not had the time to take the lap top that far apart. After 1/2 hour of trying I was not down to that level yet so I put it back together. I blew out the fans and they were better for a while.
Re: Dell Inspiron 8200
Post by klaws on Mar 26, 2007, 2:48am
The is a tool called SpeedSwitchXP, which can be used used to override the CPU speed settings. You might try this as well. It's also written by Mr. Diefer, so you'll find it at www.diefer.de as well.
Best regards, KLaus
Re: Dell Inspiron 8200
Post by griffjon on Jun 17, 2007, 12:05pm
This worked for me too. I was worried it was my d**mned fans again, but they had reasonable RPMs, so I was dumbfounded until I saw this post - Thanks!
As for the fan replacement, it's a b**ch - the penultimate step is basically using force to pry out yur motherboard (it goes back in a lot easier!) I've replaced my fans three times (long hair) and I'm deathly afraid I'll crack my mobo each time I do it. Best of luck! BTW, get the plastic scribe tool from dell or parts-people, it makes many of the steps a LOT easier.
Another fan replacement hint: make good notation of which fan plugs in where on the mobo, or you'll end up with them plugged in backwards and have to take you computer apart again!
Re: Dell Inspiron 8200
Post by roncemer on Feb 22, 2008, 2:30pm
Hello all,
I'm new to this discussion.
My 8200 just started doing this slowdown thing about a month or two ago, and I ran across this page while searching for a solution.
I wonder about the thermistor theory. Any ideas where that originated? I've done quite a bit of electronics engineering in the past, and it seems to me that any thermistor located on the motherboard, would not accurately measure the temperature of the CPU itself, but rather the CPU would need to measure its own temperature.
With that in mind, I opened up my laptop (remove keyboard, open display completely, remove top cover where power buttons are), popped open the CPU heat sink mechanism, and removed the heat sink. I then cleaned out all of the dust from the heat sink's fins (the part onto which the fans blow), cleaned off the old residual heat sink compound from the top of the CPU and the bottom of the heat sink, and put new heat sink compound on the top of the CPU. Then I put everything back together.
I got this idea because I know Dell (or UPS, who assembles the machines for Dell) tend to put too little heat sink compound on their CPUs. I know this because we've had a couple of CPUs in our servers at work, go toes-up due to overheating, and when I replaced the CPUs I noticed there wasn't much heat sink compound between the CPU and heat sink.
With new heat sink compound installed, my laptop has now been running for an hour or so, and the fans have only gone to high speed once, and then only briefly. The CPU hasn't slowed down at all.
I'm running Linux at the time (CentOS 5), but I also run XP (I have a dual-boot configuration). The CPU speed indicator applet shows a consistent 1.80 GHz.
Interestingly enough though, when my CPU would slow down, the CPU speed indicator would still show 1.80 GHz most of the time, but sometimes it would show 1.20 GHz (depending on the CPU load at the time).
Hopefully this fixes the problem. If it does NOT, then I'll post that fact later.
Re: Dell Inspiron 8200
Post by roncemer on Mar 14, 2008, 12:54pm
Well, it's been three weeks and no problems at all.
As I suspected, my problem was Dell's insufficient heat sink compound between the CPU and the heat sink. Not one time has my CPU slowed down to the point where I have to press Fn+Z to get it to speed back up.
When my fan does come in, it stays on for a while and then goes back off.
Looks like that solved it for me.
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