Fooling Dell

markjia · Post by **markjia** » Tue Jun 29, 2004 8:33 am

I have an old Dell Optiplex Gxa, and I've replaced the PSU with a spare Antec SL350S, and the case fan with a Panaflo L1A @5V (using a cable I build to use the 5V lead of one of the 4 pin connectors). Now, the problem is that the panaflo does not have a speed sensor. The Dell tries to detect the cpu fan at boot time, but as the Panaflo is connected seperately and doesn't even have a sensor, the machine refused to boot, complaining about the fan.

Now, I'm thinking that I can fool it by connecting the PSU's sensors up to the Dell's cpu fan connector. The Antec PSU has wires (connected to a 3 pin connector) that it says are meant to report the PSU fan speed. I think that this will solve my problem, but I thought I would check here before doing it.

bomba · Post by **bomba** » Tue Jun 29, 2004 9:32 am

Perhaps you can disable in BIOS, look to disable CPU fan failed detection or something similar.

markjia · Post by **markjia** » Tue Jun 29, 2004 2:39 pm

I don't think that is possible...I tried looking for it, but couldn't find anything relavent. Maybe it needs a bios upgrade, but I would rather not have to do that.

ChucuSCAD · Post by **ChucuSCAD** » Tue Jun 29, 2004 4:03 pm

Some Dells have 2 bios screens for everything(one for Joe Six Pack and another for a Tech), look carefully on ALL the screens for an administrator, or advanced, or something to that effect, I can't remember off the top of my head which models this applied to. You shold be able turn off the sensor that way.

If that doesnt work you could do what you have suggested and plug in the RPM monitor from the PS.

chucuSCAD

markjia · Post by **markjia** » Tue Jun 29, 2004 8:05 pm

Well, I tried my idea of using the psu's sensors, but that didn't work, it still said there was a fan error. I've never tried using the Antec's sensors, so I don't know for sure if it works.

I throughly looked through the BIOS but couldn't find anything. I even upgraded it, but that didn't help either.

I don't know how these fan speed sensors work (or even if the dell uses something non-standard). Is there some way to build a simple circuit to fool it? Or are there any other ideas?

Post by **Rusty075** » Tue Jun 29, 2004 8:23 pm

Here's one way...but probably not as simple as you've hoped for: How to make RPM Signal for 2-Wires Fan

mpteach · Post by **mpteach** » Tue Jun 29, 2004 9:03 pm

Rusty075 wrote:Here's one way...but probably not as simple as you've hoped for: How to make RPM Signal for 2-Wires Fan

Thats fascinating, where can i buy those to use with my panaflos?

ChucuSCAD · Post by **ChucuSCAD** » Wed Jun 30, 2004 5:37 am

I am not sure you can buy one off the shelf. You would have to hit up Radio Shack or digikey.com to get the parts.

thats really odd though that your enermax fan sensor did not work, have you modified the PS in anyway?

chucuSCAD

Post by **Rusty075** » Wed Jun 30, 2004 5:41 am

Many motherboard RPM sensors consider the fan "failed" if its spinning at less than 2500rpms or so. When cool at startup the PSU is probably spinning too slowly to be acceptable to the mobo.

bomba · Post by **bomba** » Wed Jun 30, 2004 7:08 am

Rusty075 wrote:Many motherboard RPM sensors consider the fan "failed" if its spinning at less than 2500rpms or so. When cool at startup the PSU is probably spinning too slowly to be acceptable to the mobo.

BTW, the 80mm L1A is spec'd at 1900RPM @12v, M1A is spec'd at 2450and H1A at 2950. 80mm hydrowave Panaflos w/ RPM reporting are available in medium and high speeds. Guess it would be nice to know the minimum rpm needed to boot your Dell. I'll venture to guess that a high speed BX panaflo would work fine, but not sure if it would be any quieter than the stock fan.

esn · Post by **esn** » Wed Jun 30, 2004 8:20 am

Rusty075 wrote:Many motherboard RPM sensors consider the fan "failed" if its spinning at less than 2500rpms or so. When cool at startup the PSU is probably spinning too slowly to be acceptable to the mobo.

I have an HP with a transplanted Antec PSU that doesn't have fan spped output. The bios, however, wants to see the PSU fan spinning before booting. So I've got a low volted Panaflo case fan hooked to the PSU fan header. Occasionally the system won't boot, instead returning a fan error. A second try usually boots it. I figure that the MB isn't getting the "right" signal from the fan at just the right moment. Rarely does it require more than 2 boot attempts.

markjia · Post by **markjia** » Wed Jun 30, 2004 8:34 am

Hum, that I guess it is possible that the PSU's fan is not spinning fast enough to satisfy the Dell...I tried powering on the machine a number of times, but it didn't help. The first time, it boots up and reports a fan error, every subsequent attempt just fails immediately (power off after just a second).

What if I left the orginal fan plugged in, waited for the machine to finish booting, then remove the fan? Would the machine continue to check the fan status even after boot?

esn · Post by **esn** » Wed Jun 30, 2004 11:13 am

markjia wrote:What if I left the orginal fan plugged in, waited for the machine to finish booting, then remove the fan? Would the machine continue to check the fan status even after boot?

I've unplugged various fans while the system was running to isolate noises and have never had a problem with the system shutting down suddenly. Give it a shot.

ChucuSCAD · Post by **ChucuSCAD** » Wed Jun 30, 2004 11:42 am

esn wrote: I've unplugged various fans while the system was running to isolate noises and have never had a problem with the system shutting down suddenly. Give it a shot.

The Dell however MAY shut itself off becuase it now thinks the fan is off and to protect itself shut itself off.

Do you have a case fan that has an RPM sensor you could plug into the header?

If not I think the best solution is the above mentioned kit to build.

chucuSCAD

markjia · Post by **markjia** » Wed Jun 30, 2004 1:10 pm

Thanks for the advice.

The thing is that the dell's connector is not a standard three pin molex connector...The motherboard has a 3 pin male connector that also has a sort of locking mechanism. The usual fan connectors don't fit in it. When I tested it the other day, I had to remove the pins from the replacement's plastic connector. I then squish the metal terminal so that I can install them in the dell's original connector and plug it in. So as you can imagine, it's a bit of a hassle to try another fan...

Building the kit is a bit more work than i'd like to do as well...but I appreciate all the suggestions.

I guess I will try unplugging the fan after I boot. I'll be sure to test this at a time that I can be around to monitor the system. It would make sense for the machine to try to detect the fan even after boot, but I hope Dell skimped on this when designing the system.

hofffam · Post by **hofffam** » Wed Jun 30, 2004 1:49 pm

Wouldn't it just be easier to replace the L1A with a "next best" case fan with RPM wire? You could try the Papst (a bit expensive) or another recommened fan.

markjia · Post by **markjia** » Wed Jun 30, 2004 2:09 pm

Well, I don't know for sure that "some other" fan will solve the problem. The dell could require that the fan report a high enough RPM value for it to accept the fan. I don't see why my PSU's fan speed reporting doesn't work if that 's not the case. The error message when I use the PSU's sensor is different from what I get when there is no connection at all (I can't remember the exact messages off hand). If I were to use a different fan, it might have to spin at a higher RPM in order for the machine to accept it, which almost defeats its purpose.

greeef · Post by **greeef** » Wed Jun 30, 2004 3:41 pm

Would it be possible to make a small oscilator to fool the motherboard sensor? I'm sure a simple 555 ic application would do the job.

fancontrol · Post by **fancontrol** » Wed Jun 30, 2004 7:07 pm

greeef wrote:Would it be possible to make a small oscilator to fool the motherboard sensor? I'm sure a simple 555 ic application would do the job.

I was just thinking that. If you don't care what speed gets reported, just make something to fake it out. I'd lean toward using an open-collector inverter package with an R-C pair, though; you'd need some kind of O.C. buffer to the fan input, anyway.

...doesn't someone make these already?

I might have another tach signal generator (I was just digging around in The Box of Junk tonight) but I don't think that's really what you're after.

markjia · Post by **markjia** » Thu Jul 01, 2004 12:52 am

Well, unpluging the fan after the machine doesn't work...it shuts down immediately. And stopping the fan (by sticking a pen into the fan) also shuts down the machine immediately...This is really annoying me...

So it would seem that the dell does require a certain RPM in order to work. Unfortunately, I can't find any way to determine the speed of the stock fan (the bios doesn't have anything, and speedfan and mbm don't work either).

One the only fan I have that can report its RPM (other than the Antec PSU, which doesn't work in the dell), is a 120mm evercool. So, one way I can determine the speed is to connect the evercool up to the dell with a fanmate. I can gradually turn the fan speed down until the dell reboots. Next, put the evercool back into my machine (in which speedfan/mbm works with) and figure out what speed it is spinning at (of course without touching the fanmate). Then, I can look to buy a fan w/ RPM sensing and is quiet when spinning at the desidered speed.

This is so much trouble though...

Making a fake RPM generator sounds like a better idea...is there anywhere I can find a guide to building such a device? I can read a schematic and solder, but that's about as far as my knowledge goes (designing my own circuit is a bit beyond me).

Any suggestions? Better ideas?

Regardless, thanks for all the advice so far.

fancontrol · Post by **fancontrol** » Thu Jul 01, 2004 6:02 am

I ordered samples of the MM74C906 from fairchild, should be able to whip up a ~150 Hz ( = 4500 RPM) generator without much trouble once they show up. Two resistors and a cap should do it.

But, then, by the time the parts have shown up I will loose interest and the thread will die. Whatever...

//edit: in fact, i've already lost interest. thinking back on the black hole of tach and fan boards makes me queasy. Just find a inverter with open collector outputs and pick and RC pair with a time constant of about 1/5 the period of the signal you want.

markjia · Post by **markjia** » Thu Jul 01, 2004 1:32 pm

Ya...I've sort of given up on this...

Instead, I'm moving the machine to another room. It's simpler to just tread another cat 5 wire throught the walls. The machine is headless anyway (I just VNC into it).

Thanks for the help anyways, at least I learned something.

rtsai · Post by **rtsai** » Mon Aug 02, 2004 4:01 pm

Just curious; what era is your Dell Optiplex GXa? I have an Optiplex GX-1 (1999) that has no problems with the stock fan being unplugged and plugged back in. However, I plan to replace this fan soon, so these Dell-proprietary threads are kind of worrying me ...

markjia · Post by **markjia** » Mon Aug 02, 2004 10:40 pm

I'm not really sure...I bought this real cheap last year to use as my fax server/router.

If I recall correctly, I think they were released in 97...

The machine does not have a cpu fan (just one of those black PII heatsinks), but the case fan is positioned in such a way that it almost is the cpu fan. So Dell's choice to monitor the fan makes sense.

rtsai · Post by **rtsai** » Sun Aug 08, 2004 5:10 pm

Well, to close out this thread, I am able to successfully boot my Dell Optiplex GX-1 with the proprietary 3-pin mobo CPU/case fan removed (with a generic 4-pin undervolted fan in its place), described here, albeit with a 5-second "Alert! Fan Failure!" message displayed by the BIOS before continuing to boot.